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* ipc/sem.c: fix incorrect sem_lock pairingManfred Spraul2017-01-101-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Based on the syzcaller test case from dvyukov: https://gist.githubusercontent.com/dvyukov/d0e5efefe4d7d6daed829f5c3ca26a40/raw/08d0a261fe3c987bed04fbf267e08ba04bd533ea/gistfile1.txt The slow (i.e.: failure to acquire) syscall exit from semtimedop() incorrectly assumed that the the same lock is acquired as it was at the initial syscall entry. This is wrong: - thread A: single semop semop(), sleeps - thread B: multi semop semop(), sleeps - thread A: woken up by signal/timeout With this sequence, the initial sem_lock() call locks the per-semaphore spinlock, and it is unlocked with sem_unlock(). The call at the syscall return locks the global spinlock. Because locknum is not updated, the following sem_unlock() call unlocks the per-semaphore spinlock, which is actually not locked. The fix is trivial: Use the return value from sem_lock. Fixes: 370b262c896e ("ipc/sem: avoid idr tree lookup for interrupted semop") Link: http://lkml.kernel.org/r/1482215645-22328-1-git-send-email-manfred@colorfullife.com Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reported-by: Dmitry Vyukov <dvyukov@google.com> Reported-by: Johanna Abrahamsson <johanna@mjao.org> Tested-by: Johanna Abrahamsson <johanna@mjao.org> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: avoid idr tree lookup for interrupted semopDavidlohr Bueso2016-12-141-32/+5
| | | | | | | | | | | | | | | | | | | We can avoid the idr tree lookup (albeit possibly avoiding idr_find_fast()) when being awoken in EINTR, as the semid will not change in this context while blocked. Use the sma pointer directly and take the sem_lock, then re-check for RMID races. We continue to re-check the queue.status with the lock held such that we can detect situations where we where are dealing with a spurious wakeup but another task that holds the sem_lock updated the queue.status while we were spinning for it. Once we take the lock it obviously won't change again. Being the only caller, get rid of sem_obtain_lock() altogether. Link: http://lkml.kernel.org/r/1478708774-28826-3-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: simplify wait-wake loopDavidlohr Bueso2016-12-141-56/+52
| | | | | | | | | | | | | | | Instead of using the reverse goto, we can simplify the flow and make it more language natural by just doing do-while instead. One would hope this is the standard way (or obviously just with a while bucle) that we do wait/wakeup handling in the kernel. The exact same logic is kept, just more indented. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1478708774-28826-2-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: use proper list api for pending_list wakeupsDavidlohr Bueso2016-12-141-25/+13
| | | | | | | | | | ... saves some LoC and looks cleaner than re-implementing the calls. Link: http://lkml.kernel.org/r/1474225896-10066-6-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: explicitly inline check_restartDavidlohr Bueso2016-12-141-1/+1
| | | | | | | | | | | | The compiler already does this, but make it explicit. This helper is really small and also used in update_queue's main loop, which is O(N^2) scanning. Inline and avoid the function overhead. Link: http://lkml.kernel.org/r/1474225896-10066-5-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: optimize perform_atomic_semop()Davidlohr Bueso2016-12-141-10/+102
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This is the main workhorse that deals with semop user calls such that the waitforzero or semval update operations, on the set, can complete on not as the sma currently stands. Currently, the set is iterated twice (setting semval, then backwards for the sempid value). Slowpaths, and particularly SEM_UNDO calls, must undo any altered sem when it is detected that the caller must block or has errored-out. With larger sets, there can occur situations where this involves a lot of cycles and can obviously be a suboptimal use of cached resources in shared memory. Ie, discarding CPU caches that are also calling semop and have the sembuf cached (and can complete), while the current lock holder doing the semop will block, error, or does a waitforzero operation. This patch proposes still iterating the set twice, but the first scan is read-only, and we perform the actual updates afterward, once we know that the call will succeed. In order to not suffer from the overhead of dealing with sops that act on the same sem_num, such (rare) cases use perform_atomic_semop_slow(), which is exactly what we have now. Duplicates are detected before grabbing sem_lock, and uses simple a 32/64-bit hash array variable to based on the sem_num we are working on. In addition add some comments to when we expect to the caller to block. [akpm@linux-foundation.org: coding-style fixes] [colin.king@canonical.com: ensure we left shift a ULL rather than a 32 bit integer] Link: http://lkml.kernel.org/r/20161028181129.7311-1-colin.king@canonical.com Link: http://lkml.kernel.org/r/20160921194603.GB21438@linux-80c1.suse Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Colin Ian King <colin.king@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: rework task wakeupsDavidlohr Bueso2016-12-141-180/+86
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Our sysv sems have been using the notion of lockless wakeups for a while, ever since commit 0a2b9d4c7967 ("ipc/sem.c: move wake_up_process out of the spinlock section"), in order to reduce the sem_lock hold times. This in-house pending queue can be replaced by wake_q (just like all the rest of ipc now), in that it provides the following advantages: o Simplifies and gets rid of unnecessary code. o We get rid of the IN_WAKEUP complexities. Given that wake_q_add() grabs reference to the task, if awoken due to an unrelated event, between the wake_q_add() and wake_up_q() window, we cannot race with sys_exit and the imminent call to wake_up_process(). o By not spinning IN_WAKEUP, we no longer need to disable preemption. In consequence, the wakeup paths (after schedule(), that is) must acknowledge an external signal/event, as well spurious wakeup occurring during the pending wakeup window. Obviously no changes in semantics that could be visible to the user. The fastpath is _only_ for when we know for sure that we were awoken due to a the waker's successful semop call (queue.status is not -EINTR). On a 48-core Haswell, running the ipcscale 'waitforzero' test, the following is seen with increasing thread counts: v4.8-rc5 v4.8-rc5 semopv2 Hmean sembench-sem-2 574733.00 ( 0.00%) 578322.00 ( 0.62%) Hmean sembench-sem-8 811708.00 ( 0.00%) 824689.00 ( 1.59%) Hmean sembench-sem-12 842448.00 ( 0.00%) 845409.00 ( 0.35%) Hmean sembench-sem-21 933003.00 ( 0.00%) 977748.00 ( 4.80%) Hmean sembench-sem-48 935910.00 ( 0.00%) 1004759.00 ( 7.36%) Hmean sembench-sem-79 937186.00 ( 0.00%) 983976.00 ( 4.99%) Hmean sembench-sem-234 974256.00 ( 0.00%) 1060294.00 ( 8.83%) Hmean sembench-sem-265 975468.00 ( 0.00%) 1016243.00 ( 4.18%) Hmean sembench-sem-296 991280.00 ( 0.00%) 1042659.00 ( 5.18%) Hmean sembench-sem-327 975415.00 ( 0.00%) 1029977.00 ( 5.59%) Hmean sembench-sem-358 1014286.00 ( 0.00%) 1049624.00 ( 3.48%) Hmean sembench-sem-389 972939.00 ( 0.00%) 1043127.00 ( 7.21%) Hmean sembench-sem-420 981909.00 ( 0.00%) 1056747.00 ( 7.62%) Hmean sembench-sem-451 990139.00 ( 0.00%) 1051609.00 ( 6.21%) Hmean sembench-sem-482 965735.00 ( 0.00%) 1040313.00 ( 7.72%) [akpm@linux-foundation.org: coding-style fixes] [sfr@canb.auug.org.au: merge fix for WAKE_Q to DEFINE_WAKE_Q rename] Link: http://lkml.kernel.org/r/20161122210410.5eca9fc2@canb.auug.org.au Link: http://lkml.kernel.org/r/1474225896-10066-3-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: do not call wake_sem_queue_do() prematurely ... as this call should ↵Davidlohr Bueso2016-12-141-7/+12
| | | | | | | | | | | | | | | | obviously be paired with its _prepare() counterpart. At least whenever possible, as there is no harm in calling it bogusly as we do now in a few places. Immediate error semop(2) paths that are far from ever having the task block can be simplified and avoid a few unnecessary loads on their way out of the call as it is not deeply nested. Link: http://lkml.kernel.org/r/1474225896-10066-2-git-send-email-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: add cond_resched in exit_smeNikolay Borisov2016-10-111-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In CONFIG_PREEMPT=n kernel a softlockup was observed while the for loop in exit_sem. Apparently it's possible for the loop to take quite a long time and it doesn't have a scheduling point in it. Since the codes is executing under an rcu read section this may also cause rcu stalls, which in turn block synchronize_rcu operations, which more or less de-stabilises the whole system. Fix this by introducing a cond_resched() at the beginning of the loop. So this patch fixes the following: NMI watchdog: BUG: soft lockup - CPU#10 stuck for 23s! [httpd:18119] CPU: 10 PID: 18119 Comm: httpd Tainted: G O 4.4.20-clouder2 #6 Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015 task: ffff88348d695280 ti: ffff881c95550000 task.ti: ffff881c95550000 RIP: 0010:[<ffffffff81614bc7>] [<ffffffff81614bc7>] _raw_spin_lock+0x17/0x30 RSP: 0018:ffff881c95553e40 EFLAGS: 00000246 RAX: 0000000000000000 RBX: ffff883161b1eea8 RCX: 000000000000000d RDX: 0000000000000001 RSI: 000000000000000e RDI: ffff883161b1eea4 RBP: ffff881c95553ea0 R08: ffff881c95553e68 R09: ffff883fef376f88 R10: ffff881fffb58c20 R11: ffffea0072556600 R12: ffff883161b1eea0 R13: ffff88348d695280 R14: ffff883dec427000 R15: ffff8831621672a0 FS: 0000000000000000(0000) GS:ffff881fffb40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f3b3723e020 CR3: 0000000001c0a000 CR4: 00000000001406e0 Call Trace: ? exit_sem+0x7c/0x280 do_exit+0x338/0xb40 do_group_exit+0x43/0xd0 SyS_exit_group+0x14/0x20 entry_SYSCALL_64_fastpath+0x16/0x6e Link: http://lkml.kernel.org/r/1475154992-6363-1-git-send-email-kernel@kyup.com Signed-off-by: Nikolay Borisov <kernel@kyup.com> Cc: Herton R. Krzesinski <herton@redhat.com> Cc: Fabian Frederick <fabf@skynet.be> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: fix complex_count vs. simple op raceManfred Spraul2016-10-111-55/+83
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 6d07b68ce16a ("ipc/sem.c: optimize sem_lock()") introduced a race: sem_lock has a fast path that allows parallel simple operations. There are two reasons why a simple operation cannot run in parallel: - a non-simple operations is ongoing (sma->sem_perm.lock held) - a complex operation is sleeping (sma->complex_count != 0) As both facts are stored independently, a thread can bypass the current checks by sleeping in the right positions. See below for more details (or kernel bugzilla 105651). The patch fixes that by creating one variable (complex_mode) that tracks both reasons why parallel operations are not possible. The patch also updates stale documentation regarding the locking. With regards to stable kernels: The patch is required for all kernels that include the commit 6d07b68ce16a ("ipc/sem.c: optimize sem_lock()") (3.10?) The alternative is to revert the patch that introduced the race. The patch is safe for backporting, i.e. it makes no assumptions about memory barriers in spin_unlock_wait(). Background: Here is the race of the current implementation: Thread A: (simple op) - does the first "sma->complex_count == 0" test Thread B: (complex op) - does sem_lock(): This includes an array scan. But the scan can't find Thread A, because Thread A does not own sem->lock yet. - the thread does the operation, increases complex_count, drops sem_lock, sleeps Thread A: - spin_lock(&sem->lock), spin_is_locked(sma->sem_perm.lock) - sleeps before the complex_count test Thread C: (complex op) - does sem_lock (no array scan, complex_count==1) - wakes up Thread B. - decrements complex_count Thread A: - does the complex_count test Bug: Now both thread A and thread C operate on the same array, without any synchronization. Fixes: 6d07b68ce16a ("ipc/sem.c: optimize sem_lock()") Link: http://lkml.kernel.org/r/1469123695-5661-1-git-send-email-manfred@colorfullife.com Reported-by: <felixh@informatik.uni-bremen.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: <1vier1@web.de> Cc: <stable@vger.kernel.org> [3.10+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* sysv, ipc: fix security-layer leakingFabian Frederick2016-08-021-6/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 53dad6d3a8e5 ("ipc: fix race with LSMs") updated ipc_rcu_putref() to receive rcu freeing function but used generic ipc_rcu_free() instead of msg_rcu_free() which does security cleaning. Running LTP msgsnd06 with kmemleak gives the following: cat /sys/kernel/debug/kmemleak unreferenced object 0xffff88003c0a11f8 (size 8): comm "msgsnd06", pid 1645, jiffies 4294672526 (age 6.549s) hex dump (first 8 bytes): 1b 00 00 00 01 00 00 00 ........ backtrace: kmemleak_alloc+0x23/0x40 kmem_cache_alloc_trace+0xe1/0x180 selinux_msg_queue_alloc_security+0x3f/0xd0 security_msg_queue_alloc+0x2e/0x40 newque+0x4e/0x150 ipcget+0x159/0x1b0 SyS_msgget+0x39/0x40 entry_SYSCALL_64_fastpath+0x13/0x8f Manfred Spraul suggested to fix sem.c as well and Davidlohr Bueso to only use ipc_rcu_free in case of security allocation failure in newary() Fixes: 53dad6d3a8e ("ipc: fix race with LSMs") Link: http://lkml.kernel.org/r/1470083552-22966-1-git-send-email-fabf@skynet.be Signed-off-by: Fabian Frederick <fabf@skynet.be> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: <stable@vger.kernel.org> [3.12+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* locking/spinlock: Update spin_unlock_wait() usersPeter Zijlstra2016-06-141-1/+0
| | | | | | | | | | | | | | | With the modified semantics of spin_unlock_wait() a number of explicit barriers can be removed. Also update the comment for the do_exit() usecase, as that was somewhat stale/obscure. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* locking/barriers: Introduce smp_acquire__after_ctrl_dep()Peter Zijlstra2016-06-141-12/+2
| | | | | | | | | | | | | | | | | Introduce smp_acquire__after_ctrl_dep(), this construct is not uncommon, but the lack of this barrier is. Use it to better express smp_rmb() uses in WRITE_ONCE(), the IPC semaphore code and the qspinlock code. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* ipc/sem: make semctl setting sempid consistentDavidlohr Bueso2016-03-221-2/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | | As indicated by bug#112271, Linux sets the sempid value upon semctl, and not only for semop calls. However, within semctl we only do this for SETVAL, leaving SETALL without updating the field, and therefore rather inconsistent behavior when compared to other Unices. There is really no documentation regarding this and therefore users should not make assumptions. With this patch, along with updating semctl.2 manpages, this scenario should become less ambiguous As such, set sempid on SETALL cmd. Also update some in-code documentation, specifying where the sempid is set. Passes ltp and custom testcase where a child (fork) does SETALL to the set. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Reported-by: Philip Semanchuk <linux_kernel.20.ick@spamgourmet.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Herton R. Krzesinski <herton@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* tree wide: use kvfree() than conditional kfree()/vfree()Tetsuo Handa2016-01-221-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | There are many locations that do if (memory_was_allocated_by_vmalloc) vfree(ptr); else kfree(ptr); but kvfree() can handle both kmalloc()ed memory and vmalloc()ed memory using is_vmalloc_addr(). Unless callers have special reasons, we can replace this branch with kvfree(). Please check and reply if you found problems. Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Jan Kara <jack@suse.com> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk> Reviewed-by: Andreas Dilger <andreas.dilger@intel.com> Acked-by: "Rafael J. Wysocki" <rjw@rjwysocki.net> Acked-by: David Rientjes <rientjes@google.com> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Oleg Drokin <oleg.drokin@intel.com> Cc: Boris Petkov <bp@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: update/correct memory barriersManfred Spraul2015-08-141-4/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | sem_lock() did not properly pair memory barriers: !spin_is_locked() and spin_unlock_wait() are both only control barriers. The code needs an acquire barrier, otherwise the cpu might perform read operations before the lock test. As no primitive exists inside <include/spinlock.h> and since it seems noone wants another primitive, the code creates a local primitive within ipc/sem.c. With regards to -stable: The change of sem_wait_array() is a bugfix, the change to sem_lock() is a nop (just a preprocessor redefinition to improve the readability). The bugfix is necessary for all kernels that use sem_wait_array() (i.e.: starting from 3.10). Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reported-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Kirill Tkhai <ktkhai@parallels.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: <stable@vger.kernel.org> [3.10+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()Herton R. Krzesinski2015-08-141-2/+4
| | | | | | | | | | | | | | | | After we acquire the sma->sem_perm lock in exit_sem(), we are protected against a racing IPC_RMID operation. Also at that point, we are the last user of sem_undo_list. Therefore it isn't required that we acquire or use ulp->lock. Signed-off-by: Herton R. Krzesinski <herton@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Rafael Aquini <aquini@redhat.com> CC: Aristeu Rozanski <aris@redhat.com> Cc: David Jeffery <djeffery@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc,sem: fix use after free on IPC_RMID after a task using same semaphore ↵Herton R. Krzesinski2015-08-141-6/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | set exits The current semaphore code allows a potential use after free: in exit_sem we may free the task's sem_undo_list while there is still another task looping through the same semaphore set and cleaning the sem_undo list at freeary function (the task called IPC_RMID for the same semaphore set). For example, with a test program [1] running which keeps forking a lot of processes (which then do a semop call with SEM_UNDO flag), and with the parent right after removing the semaphore set with IPC_RMID, and a kernel built with CONFIG_SLAB, CONFIG_SLAB_DEBUG and CONFIG_DEBUG_SPINLOCK, you can easily see something like the following in the kernel log: Slab corruption (Not tainted): kmalloc-64 start=ffff88003b45c1c0, len=64 000: 6b 6b 6b 6b 6b 6b 6b 6b 00 6b 6b 6b 6b 6b 6b 6b kkkkkkkk.kkkkkkk 010: ff ff ff ff 6b 6b 6b 6b ff ff ff ff ff ff ff ff ....kkkk........ Prev obj: start=ffff88003b45c180, len=64 000: 00 00 00 00 ad 4e ad de ff ff ff ff 5a 5a 5a 5a .....N......ZZZZ 010: ff ff ff ff ff ff ff ff c0 fb 01 37 00 88 ff ff ...........7.... Next obj: start=ffff88003b45c200, len=64 000: 00 00 00 00 ad 4e ad de ff ff ff ff 5a 5a 5a 5a .....N......ZZZZ 010: ff ff ff ff ff ff ff ff 68 29 a7 3c 00 88 ff ff ........h).<.... BUG: spinlock wrong CPU on CPU#2, test/18028 general protection fault: 0000 [#1] SMP Modules linked in: 8021q mrp garp stp llc nf_conntrack_ipv4 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables binfmt_misc ppdev input_leds joydev parport_pc parport floppy serio_raw virtio_balloon virtio_rng virtio_console virtio_net iosf_mbi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcspkr qxl ttm drm_kms_helper drm snd_hda_codec_generic i2c_piix4 snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore crc32c_intel virtio_pci virtio_ring virtio pata_acpi ata_generic [last unloaded: speedstep_lib] CPU: 2 PID: 18028 Comm: test Not tainted 4.2.0-rc5+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014 RIP: spin_dump+0x53/0xc0 Call Trace: spin_bug+0x30/0x40 do_raw_spin_unlock+0x71/0xa0 _raw_spin_unlock+0xe/0x10 freeary+0x82/0x2a0 ? _raw_spin_lock+0xe/0x10 semctl_down.clone.0+0xce/0x160 ? __do_page_fault+0x19a/0x430 ? __audit_syscall_entry+0xa8/0x100 SyS_semctl+0x236/0x2c0 ? syscall_trace_leave+0xde/0x130 entry_SYSCALL_64_fastpath+0x12/0x71 Code: 8b 80 88 03 00 00 48 8d 88 60 05 00 00 48 c7 c7 a0 2c a4 81 31 c0 65 8b 15 eb 40 f3 7e e8 08 31 68 00 4d 85 e4 44 8b 4b 08 74 5e <45> 8b 84 24 88 03 00 00 49 8d 8c 24 60 05 00 00 8b 53 04 48 89 RIP [<ffffffff810d6053>] spin_dump+0x53/0xc0 RSP <ffff88003750fd68> ---[ end trace 783ebb76612867a0 ]--- NMI watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [test:18053] Modules linked in: 8021q mrp garp stp llc nf_conntrack_ipv4 nf_defrag_ipv4 ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables binfmt_misc ppdev input_leds joydev parport_pc parport floppy serio_raw virtio_balloon virtio_rng virtio_console virtio_net iosf_mbi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcspkr qxl ttm drm_kms_helper drm snd_hda_codec_generic i2c_piix4 snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore crc32c_intel virtio_pci virtio_ring virtio pata_acpi ata_generic [last unloaded: speedstep_lib] CPU: 3 PID: 18053 Comm: test Tainted: G D 4.2.0-rc5+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014 RIP: native_read_tsc+0x0/0x20 Call Trace: ? delay_tsc+0x40/0x70 __delay+0xf/0x20 do_raw_spin_lock+0x96/0x140 _raw_spin_lock+0xe/0x10 sem_lock_and_putref+0x11/0x70 SYSC_semtimedop+0x7bf/0x960 ? handle_mm_fault+0xbf6/0x1880 ? dequeue_task_fair+0x79/0x4a0 ? __do_page_fault+0x19a/0x430 ? kfree_debugcheck+0x16/0x40 ? __do_page_fault+0x19a/0x430 ? __audit_syscall_entry+0xa8/0x100 ? do_audit_syscall_entry+0x66/0x70 ? syscall_trace_enter_phase1+0x139/0x160 SyS_semtimedop+0xe/0x10 SyS_semop+0x10/0x20 entry_SYSCALL_64_fastpath+0x12/0x71 Code: 47 10 83 e8 01 85 c0 89 47 10 75 08 65 48 89 3d 1f 74 ff 7e c9 c3 0f 1f 44 00 00 55 48 89 e5 e8 87 17 04 00 66 90 c9 c3 0f 1f 00 <55> 48 89 e5 0f 31 89 c1 48 89 d0 48 c1 e0 20 89 c9 48 09 c8 c9 Kernel panic - not syncing: softlockup: hung tasks I wasn't able to trigger any badness on a recent kernel without the proper config debugs enabled, however I have softlockup reports on some kernel versions, in the semaphore code, which are similar as above (the scenario is seen on some servers running IBM DB2 which uses semaphore syscalls). The patch here fixes the race against freeary, by acquiring or waiting on the sem_undo_list lock as necessary (exit_sem can race with freeary, while freeary sets un->semid to -1 and removes the same sem_undo from list_proc or when it removes the last sem_undo). After the patch I'm unable to reproduce the problem using the test case [1]. [1] Test case used below: #include <stdio.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/wait.h> #include <stdlib.h> #include <time.h> #include <unistd.h> #include <errno.h> #define NSEM 1 #define NSET 5 int sid[NSET]; void thread() { struct sembuf op; int s; uid_t pid = getuid(); s = rand() % NSET; op.sem_num = pid % NSEM; op.sem_op = 1; op.sem_flg = SEM_UNDO; semop(sid[s], &op, 1); exit(EXIT_SUCCESS); } void create_set() { int i, j; pid_t p; union { int val; struct semid_ds *buf; unsigned short int *array; struct seminfo *__buf; } un; /* Create and initialize semaphore set */ for (i = 0; i < NSET; i++) { sid[i] = semget(IPC_PRIVATE , NSEM, 0644 | IPC_CREAT); if (sid[i] < 0) { perror("semget"); exit(EXIT_FAILURE); } } un.val = 0; for (i = 0; i < NSET; i++) { for (j = 0; j < NSEM; j++) { if (semctl(sid[i], j, SETVAL, un) < 0) perror("semctl"); } } /* Launch threads that operate on semaphore set */ for (i = 0; i < NSEM * NSET * NSET; i++) { p = fork(); if (p < 0) perror("fork"); if (p == 0) thread(); } /* Free semaphore set */ for (i = 0; i < NSET; i++) { if (semctl(sid[i], NSEM, IPC_RMID)) perror("IPC_RMID"); } /* Wait for forked processes to exit */ while (wait(NULL)) { if (errno == ECHILD) break; }; } int main(int argc, char **argv) { pid_t p; srand(time(NULL)); while (1) { p = fork(); if (p < 0) { perror("fork"); exit(EXIT_FAILURE); } if (p == 0) { create_set(); goto end; } /* Wait for forked processes to exit */ while (wait(NULL)) { if (errno == ECHILD) break; }; } end: return 0; } [akpm@linux-foundation.org: use normal comment layout] Signed-off-by: Herton R. Krzesinski <herton@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Rafael Aquini <aquini@redhat.com> CC: Aristeu Rozanski <aris@redhat.com> Cc: David Jeffery <djeffery@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: rename ipc_obtain_objectDavidlohr Bueso2015-06-301-2/+2
| | | | | | | | | | ... to ipc_obtain_object_idr, which is more meaningful and makes the code slightly easier to follow. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: remove use of seq_printf return valueJoe Perches2015-04-151-12/+14
| | | | | | | | | | | | The seq_printf return value, because it's frequently misused, will eventually be converted to void. See: commit 1f33c41c03da ("seq_file: Rename seq_overflow() to seq_has_overflowed() and make public") Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc,sem: use current->state helpersDavidlohr Bueso2015-02-171-1/+1
| | | | | | | | | | Call __set_current_state() instead of assigning the new state directly. These interfaces also aid CONFIG_DEBUG_ATOMIC_SLEEP environments, keeping track of who changed the state. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: change memory barrier in sem_lock() to smp_rmb()Manfred Spraul2014-12-131-3/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When I fixed bugs in the sem_lock() logic, I was more conservative than necessary. Therefore it is safe to replace the smp_mb() with smp_rmb(). And: With smp_rmb(), semop() syscalls are up to 10% faster. The race we must protect against is: sem->lock is free sma->complex_count = 0 sma->sem_perm.lock held by thread B thread A: A: spin_lock(&sem->lock) B: sma->complex_count++; (now 1) B: spin_unlock(&sma->sem_perm.lock); A: spin_is_locked(&sma->sem_perm.lock); A: XXXXX memory barrier A: if (sma->complex_count == 0) Thread A must read the increased complex_count value, i.e. the read must not be reordered with the read of sem_perm.lock done by spin_is_locked(). Since it's about ordering of reads, smp_rmb() is sufficient. [akpm@linux-foundation.org: update sem_lock() comment, from Davidlohr] Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: fully initialize sem_array before making it visibleManfred Spraul2014-12-031-7/+8
| | | | | | | | | | | | | | | | | | ipc_addid() makes a new ipc identifier visible to everyone. New objects start as locked, so that the caller can complete the initialization after the call. Within struct sem_array, at least sma->sem_base and sma->sem_nsems are accessed without any locks, therefore this approach doesn't work. Thus: Move the ipc_addid() to the end of the initialization. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reported-by: Rik van Riel <riel@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: add a printk_once for semctl(GETNCNT/GETZCNT)Manfred Spraul2014-06-061-0/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | The actual Linux implementation for semctl(GETNCNT) and semctl(GETZCNT) always (since 0.99.10) reported a thread as sleeping on all semaphores that are listed in the semop() call. The documented behavior (both in the Linux man page and in the Single Unix Specification) is that a task should be reported on exactly one semaphore: The semaphore that caused the thread to got to sleep. This patch adds a pr_info_once() that is triggered if a thread hits the relevant case. The code triggers slightly too often, otherwise it would be necessary to replicate the old code. As there are no known users of GETNCNT or GETZCNT, this is done to prevent unnecessary bloat. The task that triggered is reported with name (tsk->comm) and pid. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Acked-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Joe Perches <joe@perches.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard compliantManfred Spraul2014-06-061-21/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | SUSv4 clearly defines how semncnt and semzcnt must be calculated: A task waits on exactly one semaphore: The semaphore from the first operation in the sop array that cannot proceed. The Linux implementation never followed the standard, it tried to count all semaphores that might be the reason why a task sleeps. This patch fixes that. Note: a) The implementation assumes that GETNCNT and GETZCNT are rare operations, therefore the code counts them only on demand. (If they wouldn't be rare, then the non-compliance would have been found earlier) b) compared to the initial version of the patch, the BUG_ONs were removed and it was clarified that the new behavior conforms to SUS. Back-compatibility concerns: Manfred: : - there is no application in Fedora that uses GETNCNT or GETZCNT. : : - application that use only single-sop semop() are also safe, the : difference only affects complex apps. : : - portable application are also safe, the new behavior is standard : compliant. : : But that's it. The old behavior existed in Linux from 0.99.something : until now. Michael: : * These operations seem to be very little used. Grepping the public : source that is contained Fedora 20 source DVD, there appear to be no : uses. Of course, this says nothing about uses in private / : non-mainstream FOSS code, but it seems likely that the same pattern : is followed there. : : * The existing behavior is hard enough to understand that I suspect : that no one understood it well enough to rely on it anyway : (especially as that behavior contradicted both man page and POSIX). : : So, there's a chance of breakage, but I estimate that it's minute. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: store which operation blocks in perform_atomic_semop()Manfred Spraul2014-06-061-0/+3
| | | | | | | | | | | | | Preparation for the next patch: In the slow-path of perform_atomic_semop(), store a pointer to the operation that caused the operation to block. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: change perform_atomic_semop parametersManfred Spraul2014-06-061-19/+19
| | | | | | | | | | | | | | Right now, perform_atomic_semop gets the content of sem_queue as individual fields. Changes that, instead pass a pointer to sem_queue. This is a preparation for the next patch: it uses sem_queue to store the reason why a task must sleep. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: remove code duplicationManfred Spraul2014-06-061-56/+51
| | | | | | | | | | | | | | count_semzcnt and count_semncnt are more of less identical. The patch creates a single function that either counts the number of tasks waiting for zero or waiting due to a decrease operation. Compared to the initial version, the BUG_ONs were removed. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: bugfix for semctl(,,GETZCNT)Manfred Spraul2014-06-061-0/+10
| | | | | | | | | | | | | | | | | | GETZCNT is supposed to return the number of threads that wait until a semaphore value becomes 0. The current implementation overlooks complex operations that contain both wait-for-zero operation and operations that alter at least one semaphore. The patch fixes that. It's intentionally copy&paste, this will be cleaned up in the next patch. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc, kernel: clear whitespacePaul McQuade2014-06-061-5/+5
| | | | | | | | trailing whitespace Signed-off-by: Paul McQuade <paulmcquad@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc, kernel: use Linux headersPaul McQuade2014-06-061-1/+1
| | | | | | | | | Use #include <linux/uaccess.h> instead of <asm/uaccess.h> Use #include <linux/types.h> instead of <asm/types.h> Signed-off-by: Paul McQuade <paulmcquad@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: constify ipc_opsMathias Krause2014-06-061-5/+5
| | | | | | | | | | | | | | | | There is no need to recreate the very same ipc_ops structure on every kernel entry for msgget/semget/shmget. Just declare it static and be done with it. While at it, constify it as we don't modify the structure at runtime. Found in the PaX patch, written by the PaX Team. Signed-off-by: Mathias Krause <minipli@googlemail.com> Cc: PaX Team <pageexec@freemail.hu> Cc: Davidlohr Bueso <davidlohr@hp.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: remove braces for single statementsDavidlohr Bueso2014-01-271-5/+3
| | | | | | | | | | | | Deal with checkpatch messages: WARNING: braces {} are not necessary for single statement blocks Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: standardize code commentsDavidlohr Bueso2014-01-271-13/+11
| | | | | | | | | | | | IPC commenting style is all over the place, *specially* in util.c. This patch orders things a bit. Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: whitespace cleanupManfred Spraul2014-01-271-48/+48
| | | | | | | | | | | | | | | | | | | | | | | The ipc code does not adhere the typical linux coding style. This patch fixes lots of simple whitespace errors. - mostly autogenerated by scripts/checkpatch.pl -f --fix \ --types=pointer_location,spacing,space_before_tab - one manual fixup (keep structure members tab-aligned) - removal of additional space_before_tab that were not found by --fix Tested with some of my msg and sem test apps. Andrew: Could you include it in -mm and move it towards Linus' tree? Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Suggested-by: Li Bin <huawei.libin@huawei.com> Cc: Joe Perches <joe@perches.com> Acked-by: Rafael Aquini <aquini@redhat.com> Cc: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: change kern_ipc_perm.deleted type to boolRafael Aquini2014-01-271-1/+1
| | | | | | | | | | | | | struct kern_ipc_perm.deleted is meant to be used as a boolean toggle, and the changes introduced by this patch are just to make the case explicit. Signed-off-by: Rafael Aquini <aquini@redhat.com> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Greg Thelen <gthelen@google.com> Acked-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: introduce ipc_valid_object() helper to sort out IPC_RMID racesRafael Aquini2014-01-271-8/+16
| | | | | | | | | | | | | | | | | | | | After the locking semantics for the SysV IPC API got improved, a couple of IPC_RMID race windows were opened because we ended up dropping the 'kern_ipc_perm.deleted' check performed way down in ipc_lock(). The spotted races got sorted out by re-introducing the old test within the racy critical sections. This patch introduces ipc_valid_object() to consolidate the way we cope with IPC_RMID races by using the same abstraction across the API implementation. Signed-off-by: Rafael Aquini <aquini@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Greg Thelen <gthelen@google.com> Reviewed-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: avoid overflow of semop undo (semadj) valuePetr Mladek2014-01-271-11/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When trying to understand semop code, I found a small mistake in the check for semadj (undo) value overflow. The new undo value is not stored immediately and next potential checks are done against the old value. The failing scenario is not much practical. One semop call has to do more operations on the same semaphore. Also semval and semadj must have different values, so there has to be some operations without SEM_UNDO flag. For example: struct sembuf depositor_op[1]; struct sembuf collector_op[2]; depositor_op[0].sem_num = 0; depositor_op[0].sem_op = 20000; depositor_op[0].sem_flg = 0; collector_op[0].sem_num = 0; collector_op[0].sem_op = -10000; collector_op[0].sem_flg = SEM_UNDO; collector_op[1].sem_num = 0; collector_op[1].sem_op = -10000; collector_op[1].sem_flg = SEM_UNDO; if (semop(semid, depositor_op, 1) == -1) { perror("Failed to do 1st deposit"); return 1; } if (semop(semid, collector_op, 2) == -1) { perror("Failed to do 1st collect"); return 1; } if (semop(semid, depositor_op, 1) == -1) { perror("Failed to do 2nd deposit"); return 1; } if (semop(semid, collector_op, 2) == -1) { perror("Failed to do 2nd collect"); return 1; } return 0; It passes without error now but the semadj value has overflown in the 2nd collector operation. [akpm@linux-foundation.org: restore lessened scope of local `undo'] [davidlohr@hp.com: correct header comment for perform_atomic_semop] Signed-off-by: Petr Mladek <pmladek@suse.cz> Acked-by: Davidlohr Bueso <davidlohr@hp.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Cc: Jiri Kosina <jkosina@suse.cz> Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: synchronize semop and semctl with IPC_RMIDManfred Spraul2013-10-161-13/+29
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | After acquiring the semlock spinlock, operations must test that the array is still valid. - semctl() and exit_sem() would walk stale linked lists (ugly, but should be ok: all lists are empty) - semtimedop() would sleep forever - and if woken up due to a signal - access memory after free. The patch also: - standardizes the tests for .deleted, so that all tests in one function leave the function with the same approach. - unconditionally tests for .deleted immediately after every call to sem_lock - even it it means that for semctl(GETALL), .deleted will be tested twice. Both changes make the review simpler: After every sem_lock, there must be a test of .deleted, followed by a goto to the cleanup code (if the function uses "goto cleanup"). The only exception is semctl_down(): If sem_ids().rwsem is locked, then the presence in ids->ipcs_idr is equivalent to !.deleted, thus no additional test is required. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Mike Galbraith <efault@gmx.de> Acked-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: update sem_otime for all operationsManfred Spraul2013-09-301-13/+29
| | | | | | | | | | | | | | | | | | | | | | In commit 0a2b9d4c7967 ("ipc/sem.c: move wake_up_process out of the spinlock section"), the update of semaphore's sem_otime(last semop time) was moved to one central position (do_smart_update). But since do_smart_update() is only called for operations that modify the array, this means that wait-for-zero semops do not update sem_otime anymore. The fix is simple: Non-alter operations must update sem_otime. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Reported-by: Jia He <jiakernel@gmail.com> Tested-by: Jia He <jiakernel@gmail.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: synchronize the proc interfaceManfred Spraul2013-09-301-0/+8
| | | | | | | | | | | | | | | | | The proc interface is not aware of sem_lock(), it instead calls ipc_lock_object() directly. This means that simple semop() operations can run in parallel with the proc interface. Right now, this is uncritical, because the implementation doesn't do anything that requires a proper synchronization. But it is dangerous and therefore should be fixed. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: optimize sem_lock()Manfred Spraul2013-09-301-0/+8
| | | | | | | | | | | | | | | | | | | Operations that need access to the whole array must guarantee that there are no simple operations ongoing. Right now this is achieved by spin_unlock_wait(sem->lock) on all semaphores. If complex_count is nonzero, then this spin_unlock_wait() is not necessary, because it was already performed in the past by the thread that increased complex_count and even though sem_perm.lock was dropped inbetween, no simple operation could have started, because simple operations cannot start when complex_count is non-zero. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Rik van Riel <riel@redhat.com> Reviewed-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: fix race in sem_lock()Manfred Spraul2013-09-301-44/+78
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The exclusion of complex operations in sem_lock() is insufficient: after acquiring the per-semaphore lock, a simple op must first check that sem_perm.lock is not locked and only after that test check complex_count. The current code does it the other way around - and that creates a race. Details are below. The patch is a complete rewrite of sem_lock(), based in part on the code from Mike Galbraith. It removes all gotos and all loops and thus the risk of livelocks. I have tested the patch (together with the next one) on my i3 laptop and it didn't cause any problems. The bug is probably also present in 3.10 and 3.11, but for these kernels it might be simpler just to move the test of sma->complex_count after the spin_is_locked() test. Details of the bug: Assume: - sma->complex_count = 0. - Thread 1: semtimedop(complex op that must sleep) - Thread 2: semtimedop(simple op). Pseudo-Trace: Thread 1: sem_lock(): acquire sem_perm.lock Thread 1: sem_lock(): check for ongoing simple ops Nothing ongoing, thread 2 is still before sem_lock(). Thread 1: try_atomic_semop() <<< preempted. Thread 2: sem_lock(): static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, int nsops) { int locknum; again: if (nsops == 1 && !sma->complex_count) { struct sem *sem = sma->sem_base + sops->sem_num; /* Lock just the semaphore we are interested in. */ spin_lock(&sem->lock); /* * If sma->complex_count was set while we were spinning, * we may need to look at things we did not lock here. */ if (unlikely(sma->complex_count)) { spin_unlock(&sem->lock); goto lock_array; } <<<<<<<<< <<< complex_count is still 0. <<< <<< Here it is preempted <<<<<<<<< Thread 1: try_atomic_semop() returns, notices that it must sleep. Thread 1: increases sma->complex_count. Thread 1: drops sem_perm.lock Thread 2: /* * Another process is holding the global lock on the * sem_array; we cannot enter our critical section, * but have to wait for the global lock to be released. */ if (unlikely(spin_is_locked(&sma->sem_perm.lock))) { spin_unlock(&sem->lock); spin_unlock_wait(&sma->sem_perm.lock); goto again; } <<< sem_perm.lock already dropped, thus no "goto again;" locknum = sops->sem_num; Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Mike Galbraith <bitbucket@online.de> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: <stable@vger.kernel.org> [3.10+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: fix race with LSMsDavidlohr Bueso2013-09-241-16/+18
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, IPC mechanisms do security and auditing related checks under RCU. However, since security modules can free the security structure, for example, through selinux_[sem,msg_queue,shm]_free_security(), we can race if the structure is freed before other tasks are done with it, creating a use-after-free condition. Manfred illustrates this nicely, for instance with shared mem and selinux: -> do_shmat calls rcu_read_lock() -> do_shmat calls shm_object_check(). Checks that the object is still valid - but doesn't acquire any locks. Then it returns. -> do_shmat calls security_shm_shmat (e.g. selinux_shm_shmat) -> selinux_shm_shmat calls ipc_has_perm() -> ipc_has_perm accesses ipc_perms->security shm_close() -> shm_close acquires rw_mutex & shm_lock -> shm_close calls shm_destroy -> shm_destroy calls security_shm_free (e.g. selinux_shm_free_security) -> selinux_shm_free_security calls ipc_free_security(&shp->shm_perm) -> ipc_free_security calls kfree(ipc_perms->security) This patch delays the freeing of the security structures after all RCU readers are done. Furthermore it aligns the security life cycle with that of the rest of IPC - freeing them based on the reference counter. For situations where we need not free security, the current behavior is kept. Linus states: "... the old behavior was suspect for another reason too: having the security blob go away from under a user sounds like it could cause various other problems anyway, so I think the old code was at least _prone_ to bugs even if it didn't have catastrophic behavior." I have tested this patch with IPC testcases from LTP on both my quad-core laptop and on a 64 core NUMA server. In both cases selinux is enabled, and tests pass for both voluntary and forced preemption models. While the mentioned races are theoretical (at least no one as reported them), I wanted to make sure that this new logic doesn't break anything we weren't aware of. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc: rename ids->rw_mutexDavidlohr Bueso2013-09-111-12/+12
| | | | | | | | | | | | Since in some situations the lock can be shared for readers, we shouldn't be calling it a mutex, rename it to rwsem. Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: rename try_atomic_semop() to perform_atomic_semop(), docu updateManfred Spraul2013-07-091-11/+21
| | | | | | | | | | | | | | | | | | Cleanup: Some minor points that I noticed while writing the previous patches 1) The name try_atomic_semop() is misleading: The function performs the operation (if it is possible). 2) Some documentation updates. No real code change, a rename and documentation changes. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: replace shared sem_otime with per-semaphore valueManfred Spraul2013-07-091-6/+31
| | | | | | | | | | | | | | | | | | sem_otime contains the time of the last semaphore operation that completed successfully. Every operation updates this value, thus access from multiple cpus can cause thrashing. Therefore the patch replaces the variable with a per-semaphore variable. The per-array sem_otime is only calculated when required. No performance improvement on a single-socket i3 - only important for larger systems. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: always use only one queue for alter operationsManfred Spraul2013-07-091-40/+88
| | | | | | | | | | | | | | | | | | | | | | | | | | There are two places that can contain alter operations: - the global queue: sma->pending_alter - the per-semaphore queues: sma->sem_base[].pending_alter. Since one of the queues must be processed first, this causes an odd priorization of the wakeups: complex operations have priority over simple ops. The patch restores the behavior of linux <=3.0.9: The longest waiting operation has the highest priority. This is done by using only one queue: - if there are complex ops, then sma->pending_alter is used. - otherwise, the per-semaphore queues are used. As a side effect, do_smart_update_queue() becomes much simpler: no more goto logic. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem: separate wait-for-zero and alter tasks into seperate queuesManfred Spraul2013-07-091-60/+151
| | | | | | | | | | | | | | | | Introduce separate queues for operations that do not modify the semaphore values. Advantages: - Simpler logic in check_restart(). - Faster update_queue(): Right now, all wait-for-zero operations are always tested, even if the semaphore value is not 0. - wait-for-zero gets again priority, as in linux <=3.0.9 Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* ipc/sem.c: cacheline align the semaphore structuresManfred Spraul2013-07-091-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | As now each semaphore has its own spinlock and parallel operations are possible, give each semaphore its own cacheline. On a i3 laptop, this gives up to 28% better performance: #semscale 10 | grep "interleave 2" - before: Cpus 1, interleave 2 delay 0: 36109234 in 10 secs Cpus 2, interleave 2 delay 0: 55276317 in 10 secs Cpus 3, interleave 2 delay 0: 62411025 in 10 secs Cpus 4, interleave 2 delay 0: 81963928 in 10 secs -after: Cpus 1, interleave 2 delay 0: 35527306 in 10 secs Cpus 2, interleave 2 delay 0: 70922909 in 10 secs <<< + 28% Cpus 3, interleave 2 delay 0: 80518538 in 10 secs Cpus 4, interleave 2 delay 0: 89115148 in 10 secs <<< + 8.7% i3, with 2 cores and with hyperthreading enabled. Interleave 2 in order use first the full cores. HT partially hides the delay from cacheline trashing, thus the improvement is "only" 8.7% if 4 threads are running. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Rik van Riel <riel@redhat.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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