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| author | Jan Stancek <jstancek@redhat.com> | 2019-08-26 10:31:13 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-09-06 10:23:27 +0200 |
| commit | 931424d0781ea980d81c8d848a3a78dd9ed8885b (patch) | |
| tree | b0046f8ebe0f6629d7d451b3c52ded041cb7c332 /kernel | |
| parent | 5faa01cc2b1fc55ced2103d31fd68a20ce0427ec (diff) | |
| download | linux-stable-931424d0781ea980d81c8d848a3a78dd9ed8885b.tar.gz linux-stable-931424d0781ea980d81c8d848a3a78dd9ed8885b.tar.bz2 linux-stable-931424d0781ea980d81c8d848a3a78dd9ed8885b.zip | |
locking/rwsem: Add missing ACQUIRE to read_slowpath exit when queue is empty
[ Upstream commit e1b98fa316648420d0434d9ff5b92ad6609ba6c3 ]
LTP mtest06 has been observed to occasionally hit "still mapped when
deleted" and following BUG_ON on arm64.
The extra mapcount originated from pagefault handler, which handled
pagefault for vma that has already been detached. vma is detached
under mmap_sem write lock by detach_vmas_to_be_unmapped(), which
also invalidates vmacache.
When the pagefault handler (under mmap_sem read lock) calls
find_vma(), vmacache_valid() wrongly reports vmacache as valid.
After rwsem down_read() returns via 'queue empty' path (as of v5.2),
it does so without an ACQUIRE on sem->count:
down_read()
__down_read()
rwsem_down_read_failed()
__rwsem_down_read_failed_common()
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
if (atomic_long_read(&sem->count) >= 0) {
raw_spin_unlock_irq(&sem->wait_lock);
return sem;
The problem can be reproduced by running LTP mtest06 in a loop and
building the kernel (-j $NCPUS) in parallel. It does reproduces since
v4.20 on arm64 HPE Apollo 70 (224 CPUs, 256GB RAM, 2 nodes). It
triggers reliably in about an hour.
The patched kernel ran fine for 10+ hours.
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dbueso@suse.de
Fixes: 4b486b535c33 ("locking/rwsem: Exit read lock slowpath if queue empty & no writer")
Link: https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 0b1f77957240..397dedc58432 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -454,6 +454,8 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state) * been set in the count. */ if (atomic_long_read(&sem->count) >= 0) { + /* Provide lock ACQUIRE */ + smp_acquire__after_ctrl_dep(); raw_spin_unlock_irq(&sem->wait_lock); rwsem_set_reader_owned(sem); lockevent_inc(rwsem_rlock_fast); |