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* Merge tag 'trace-3.12' of ↵Linus Torvalds2013-09-091-1/+1
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing updates from Steven Rostedt: "Not much changes for the 3.12 merge window. The major tracing changes are still in flux, and will have to wait for 3.13. The changes for 3.12 are mostly clean ups and minor fixes. H Peter Anvin added a check to x86_32 static function tracing that helps a small segment of the kernel community. Oleg Nesterov had a few changes from 3.11, but were mostly clean ups and not worth pushing in the -rc time frame. Li Zefan had small clean up with annotating a raw_init with __init. I fixed a slight race in updating function callbacks, but the race is so small and the bug that happens when it occurs is so minor it's not even worth pushing to stable. The only real enhancement is from Alexander Z Lam that made the tracing_cpumask work for trace buffer instances, instead of them all sharing a global cpumask" * tag 'trace-3.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: ftrace/rcu: Do not trace debug_lockdep_rcu_enabled() x86-32, ftrace: Fix static ftrace when early microcode is enabled ftrace: Fix a slight race in modifying what function callback gets traced tracing: Make tracing_cpumask available for all instances tracing: Kill the !CONFIG_MODULES code in trace_events.c tracing: Don't pass file_operations array to event_create_dir() tracing: Kill trace_create_file_ops() and friends tracing/syscalls: Annotate raw_init function with __init
| * ftrace/rcu: Do not trace debug_lockdep_rcu_enabled()Steven Rostedt (Red Hat)2013-09-051-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | The function debug_lockdep_rcu_enabled() is part of the RCU lockdep debugging, and is called very frequently. I found that if I enable a lot of debugging and run the function graph tracer, this function can cause a live lock of the system. We don't usually trace lockdep infrastructure, no need to trace this either. Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
* | rcu: Simplify debug-objects fixupsPaul E. McKenney2013-08-181-100/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current debug-objects fixups are complex and heavyweight, and the fixups are not complete: Even with the fixups, RCU's callback lists can still be corrupted. This commit therefore strips the fixups down to their minimal form, eliminating two of the three. It would be even better if (for example) call_rcu() simply leaked any problematic callbacks, but for that to happen, the debug-objects system would need to inform its caller of suspicious situations. This is the subject of a later commit in this series. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Sedat Dilek <sedat.dilek@gmail.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Rik van Riel <riel@surriel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* | rcu: Add const annotation to char * for RCU tracepoints and functionsSteven Rostedt (Red Hat)2013-07-291-1/+1
|/ | | | | | | | | | | | | | | | | All the RCU tracepoints and functions that reference char pointers do so with just 'char *' even though they do not modify the contents of the string itself. This will cause warnings if a const char * is used in one of these functions. The RCU tracepoints store the pointer to the string to refer back to them when the trace output is displayed. As this can be minutes, hours or even days later, those strings had better be constant. This change also opens the door to allow the RCU tracepoint strings and their addresses to be exported so that userspace tracing tools can translate the contents of the pointers of the RCU tracepoints. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
*-. Merge branches 'cbnum.2013.06.10a', 'doc.2013.06.10a', 'fixes.2013.06.10a', ↵Paul E. McKenney2013-06-101-28/+1
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'srcu.2013.06.10a' and 'tiny.2013.06.10a' into HEAD cbnum.2013.06.10a: Apply simplifications stemming from the new callback numbering. doc.2013.06.10a: Documentation updates. fixes.2013.06.10a: Miscellaneous fixes. srcu.2013.06.10a: Updates to SRCU. tiny.2013.06.10a: Eliminate TINY_PREEMPT_RCU.
| | * rcu: Shrink TINY_RCU by moving exit_rcu()Paul E. McKenney2013-06-101-25/+1
| |/ |/| | | | | | | | | | | | | | | | | | | | | Now that TINY_PREEMPT_RCU is no more, exit_rcu() is always an empty function. But if TINY_RCU is going to have an empty function, it should be in include/linux/rcutiny.h, where it does not bloat the kernel. This commit therefore moves exit_rcu() out of kernel/rcupdate.c to kernel/rcutree_plugin.h, and places a static inline empty function in include/linux/rcutiny.h in order to shrink TINY_RCU a bit. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| * rcu: Merge adjacent identical ifdefsPaul E. McKenney2013-06-101-3/+0
|/ | | | | | | | Two ifdefs in kernel/rcupdate.c now have identical conditions with nothing between them, so the commit merges them into a single ifdef. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
*-. Merge branches 'doctorture.2013.01.29a', 'fixes.2013.01.26a', ↵Paul E. McKenney2013-01-281-0/+51
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'tagcb.2013.01.24a' and 'tiny.2013.01.29b' into HEAD doctorture.2013.01.11a: Changes to rcutorture and to RCU documentation. fixes.2013.01.26a: Miscellaneous fixes. tagcb.2013.01.24a: Tag RCU callbacks with grace-period number to simplify callback advancement. tiny.2013.01.29b: Enhancements to uniprocessor handling in tiny RCU.
| | * rcu: Provide RCU CPU stall warnings for tiny RCUPaul E. McKenney2013-01-281-0/+51
| |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tiny RCU has historically omitted RCU CPU stall warnings in order to reduce memory requirements, however, lack of these warnings caused Thomas Gleixner some debugging pain recently. Therefore, this commit adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory footprint small, while still enabling CPU stall warnings in kernels built to enable them. Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON config variable to simplify #if expressions. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* / rcu: Reduce rcutorture tracingPaul E. McKenney2013-01-081-3/+6
|/ | | | | | | | | | | | | | | | Currently, rcutorture traces every read-side access. This can be problematic because even a two-minute rcutorture run on a two-CPU system can generate 28,853,363 reads. Normally, only a failing read is of interest, so this commit traces adjusts rcutorture's tracing to only trace failing reads. The resulting event tracing records the time and the ->completed value captured at the beginning of the RCU read-side critical section, allowing correlation with other event-tracing messages. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Add fix to build problem located by Randy Dunlap based on diagnosis by Steven Rostedt. ]
* rcu: Add a module parameter to force use of expedited RCU primitivesAntti P Miettinen2012-10-231-0/+3
| | | | | | | | | | | | | | | | | | There have been some embedded applications that would benefit from use of expedited grace-period primitives. In some ways, this is similar to synchronize_net() doing either a normal or an expedited grace period depending on lock state, but with control outside of the kernel. This commit therefore adds rcu_expedited boot and sysfs parameters that cause the kernel to substitute expedited primitives for the normal grace-period primitives. [ paulmck: Add trace/event/rcu.h to kernel/srcu.c to avoid build error. Get rid of infinite loop through contention path.] Signed-off-by: Antti P Miettinen <amiettinen@nvidia.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add PROVE_RCU_DELAY to provoke difficult racesPaul E. McKenney2012-09-231-0/+4
| | | | | | | | | | | | | | | There have been some recent bugs that were triggered only when preemptible RCU's __rcu_read_unlock() was preempted just after setting ->rcu_read_lock_nesting to INT_MIN, which is a low-probability event. Therefore, reproducing those bugs (to say nothing of gaining confidence in alleged fixes) was quite difficult. This commit therefore creates a new debug-only RCU kernel config option that forces a short delay in __rcu_read_unlock() to increase the probability of those sorts of bugs occurring. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Consolidate tree/tiny __rcu_read_{,un}lock() implementationsPaul E. McKenney2012-07-021-0/+44
| | | | | | | | | | The CONFIG_TREE_PREEMPT_RCU and CONFIG_TINY_PREEMPT_RCU versions of __rcu_read_lock() and __rcu_read_unlock() are identical, so this commit consolidates them into kernel/rcupdate.h. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Make exit_rcu() more precise and consolidatePaul E. McKenney2012-05-021-0/+28
| | | | | | | | | | | | | | | | | | | | | | | | | | When running preemptible RCU, if a task exits in an RCU read-side critical section having blocked within that same RCU read-side critical section, the task must be removed from the list of tasks blocking a grace period (perhaps the current grace period, perhaps the next grace period, depending on timing). The exit() path invokes exit_rcu() to do this cleanup. However, the current implementation of exit_rcu() needlessly does the cleanup even if the task did not block within the current RCU read-side critical section, which wastes time and needlessly increases the size of the state space. Fix this by only doing the cleanup if the current task is actually on the list of tasks blocking some grace period. While we are at it, consolidate the two identical exit_rcu() functions into a single function. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Linus Torvalds <torvalds@linux-foundation.org> Conflicts: kernel/rcupdate.c
* rcu: Check for illegal use of RCU from offlined CPUsPaul E. McKenney2012-02-211-0/+5
| | | | | | | | | | | | | | | | | Although it is legal to use RCU during early boot, it is anything but legal to use RCU at runtime from an offlined CPU. After all, RCU explicitly ignores offlined CPUs. This commit therefore adds checks for runtime use of RCU from offlined CPUs. These checks are not perfect, in particular, they can be subverted through use of things like rcu_dereference_raw(). Note that it is not possible to put checks in rcu_read_lock() and friends due to the fact that these primitives are used in code that might be used under either RCU or lock-based protection, which means that checking rcu_read_lock() gets you fat piles of false positives. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Detect illegal rcu dereference in extended quiescent stateFrederic Weisbecker2011-12-111-0/+2
| | | | | | | | | | | | | | | | | | | | | | | Report that none of the rcu read lock maps are held while in an RCU extended quiescent state (the section between rcu_idle_enter() and rcu_idle_exit()). This helps detect any use of rcu_dereference() and friends from within the section in idle where RCU is not allowed. This way we can guarantee an extended quiescent window where the CPU can be put in dyntick idle mode or can simply aoid to be part of any global grace period completion while in the idle loop. Uses of RCU from such mode are totally ignored by RCU, hence the importance of these checks. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Add failure tracing to rcutorturePaul E. McKenney2011-12-111-0/+10
| | | | | | | | | Trace the rcutorture RCU accesses and dump the trace buffer when the first failure is detected. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* kernel: Map most files to use export.h instead of module.hPaul Gortmaker2011-10-311-1/+1
| | | | | | | | | | | | | | | | The changed files were only including linux/module.h for the EXPORT_SYMBOL infrastructure, and nothing else. Revector them onto the isolated export header for faster compile times. Nothing to see here but a whole lot of instances of: -#include <linux/module.h> +#include <linux/export.h> This commit is only changing the kernel dir; next targets will probably be mm, fs, the arch dirs, etc. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
* rcu: Add event-tracing for RCU callback invocationPaul E. McKenney2011-09-281-0/+5
| | | | | | | | | There was recently some controversy about the overhead of invoking RCU callbacks. Add TRACE_EVENT()s to obtain fine-grained timings for the start and stop of a batch of callbacks and also for each callback invoked. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Abstract common code for RCU grace-period-wait primitivesPaul E. McKenney2011-09-281-1/+20
| | | | | | | | | Pull the code that waits for an RCU grace period into a single function, which is then called by synchronize_rcu() and friends in the case of TREE_RCU and TREE_PREEMPT_RCU, and from rcu_barrier() and friends in the case of TINY_RCU and TINY_PREEMPT_RCU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* atomic: use <linux/atomic.h>Arun Sharma2011-07-261-1/+1
| | | | | | | | | | | | | | This allows us to move duplicated code in <asm/atomic.h> (atomic_inc_not_zero() for now) to <linux/atomic.h> Signed-off-by: Arun Sharma <asharma@fb.com> Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David Miller <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* rcu: Use WARN_ON_ONCE for DEBUG_OBJECTS_RCU_HEAD warningsPaul E. McKenney2011-05-051-6/+6
| | | | | | | Avoid additional multiple-warning confusion in memory-corruption scenarios. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPTMathieu Desnoyers2011-05-051-5/+21
| | | | | | | | | The prohibition of DEBUG_OBJECTS_RCU_HEAD from !PREEMPT was due to the fixup actions. So just produce a warning from !PREEMPT. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT.Paul E. McKenney2011-03-041-0/+5
| | | | | | | | The build will break if you change the Kconfig to allow DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning near where the breakage would occur. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcupdate: remove dead codeAmerigo Wang2011-03-041-5/+0
| | | | | | | | | DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT, so #ifndef CONFIG_PREEMPT is totally useless in kernel/rcupdate.c. Signed-off-by: WANG Cong <amwang@redhat.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* Merge branch 'rcu/urgent' of ↵Ingo Molnar2010-10-071-1/+1
|\ | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu into core/rcu
| * rcu: move check from rcu_dereference_bh to rcu_read_lock_bh_heldPaul E. McKenney2010-10-051-1/+1
| | | | | | | | | | | | | | | | As suggested by Linus, push the irqs_disabled() down to the rcu_read_lock_bh_held() level so that all callers get the benefit of the correct check. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | rcu: define __rcu address space modifier for sparsePaul E. McKenney2010-08-191-2/+4
|/ | | | | | | | | | | | | | | | | | | | | | | | This commit provides definitions for the __rcu annotation defined earlier. This annotation permits sparse to check for correct use of RCU-protected pointers. If a pointer that is annotated with __rcu is accessed directly (as opposed to via rcu_dereference(), rcu_assign_pointer(), or one of their variants), sparse can be made to complain. To enable such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER kernel configuration option. Please note that these sparse complaints are intended to be a debugging aid, -not- a code-style-enforcement mechanism. There are special rcu_dereference_protected() and rcu_access_pointer() accessors for use when RCU read-side protection is not required, for example, when no other CPU has access to the data structure in question or while the current CPU hold the update-side lock. This patch also updates a number of docbook comments that were showing their age. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Christopher Li <sparse@chrisli.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* tree/tiny rcu: Add debug RCU head objectsMathieu Desnoyers2010-06-141-0/+160
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Helps finding racy users of call_rcu(), which results in hangs because list entries are overwritten and/or skipped. Changelog since v4: - Bissectability is now OK - Now generate a WARN_ON_ONCE() for non-initialized rcu_head passed to call_rcu(). Statically initialized objects are detected with object_is_static(). - Rename rcu_head_init_on_stack to init_rcu_head_on_stack. - Remove init_rcu_head() completely. Changelog since v3: - Include comments from Lai Jiangshan This new patch version is based on the debugobjects with the newly introduced "active state" tracker. Non-initialized entries are all considered as "statically initialized". An activation fixup (triggered by call_rcu()) takes care of performing the debug object initialization without issuing any warning. Since we cannot increase the size of struct rcu_head, I don't see much room to put an identifier for statically initialized rcu_head structures. So for now, we have to live without "activation without explicit init" detection. But the main purpose of this debug option is to detect double-activations (double call_rcu() use of a rcu_head before the callback is executed), which is correctly addressed here. This also detects potential internal RCU callback corruption, which would cause the callbacks to be executed twice. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: David S. Miller <davem@davemloft.net> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> CC: akpm@linux-foundation.org CC: mingo@elte.hu CC: laijs@cn.fujitsu.com CC: dipankar@in.ibm.com CC: josh@joshtriplett.org CC: dvhltc@us.ibm.com CC: niv@us.ibm.com CC: tglx@linutronix.de CC: peterz@infradead.org CC: rostedt@goodmis.org CC: Valdis.Kletnieks@vt.edu CC: dhowells@redhat.com CC: eric.dumazet@gmail.com CC: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
* rcu: slim down rcutiny by removing rcu_scheduler_active and friendsPaul E. McKenney2010-05-101-19/+0
| | | | | | | | | TINY_RCU does not need rcu_scheduler_active unless CONFIG_DEBUG_LOCK_ALLOC. So conditionally compile rcu_scheduler_active in order to slim down rcutiny a bit more. Also gets rid of an EXPORT_SYMBOL_GPL, which is responsible for most of the slimming. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: create rcu_my_thread_group_empty() wrapperPaul E. McKenney2010-05-061-0/+11
| | | | | | | | | | | Some RCU-lockdep splat repairs need to know whether they are running in a single-threaded process. Unfortunately, the thread_group_empty() primitive is defined in sched.h, and can induce #include hell. This commit therefore introduces a rcu_my_thread_group_empty() wrapper that is defined in rcupdate.c, thus avoiding the need to include sched.h everywhere. Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
* rcu: Make RCU lockdep check the lockdep_recursion variablePaul E. McKenney2010-04-191-0/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | The lockdep facility temporarily disables lockdep checking by incrementing the current->lockdep_recursion variable. Such disabling happens in NMIs and in other situations where lockdep might expect to recurse on itself. This patch therefore checks current->lockdep_recursion, disabling RCU lockdep splats when this variable is non-zero. In addition, this patch removes the "likely()", as suggested by Lai Jiangshan. Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Reported-by: David Miller <davem@davemloft.net> Tested-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com Cc: eric.dumazet@gmail.com LKML-Reference: <20100415195039.GA22623@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Make rcu_read_lock_bh_held() allow for disabled BHPaul E. McKenney2010-03-161-0/+23
| | | | | | | | | | | | | | | | | | | | | | | | | Disabling BH can stand in for rcu_read_lock_bh(), and this patch updates rcu_read_lock_bh_held() to allow for this. In order to avoid include-file hell, this function is moved out of line to kernel/rcupdate.c. This fixes a false positive RCU warning. Reported-by: Arnd Bergmann <arnd@arndb.de> Reported-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <20100316000343.GA25857@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Export rcu_scheduler_activePaul E. McKenney2010-02-261-0/+1
| | | | | | | | | | | | | | | | | | | | | Kernel modules using rcu_read_lock_sched_held() must now have access to rcu_scheduler_active, so it must be exported. This should fix the fix for the boot-time RCU-lockdep splat. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <20100226030230.GA7743@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Make rcu_read_lock_sched_held() take boot time into accountPaul E. McKenney2010-02-261-0/+18
| | | | | | | | | | | | | | | | | | | | Before the scheduler starts, all tasks are non-preemptible by definition. So, during that time, rcu_read_lock_sched_held() needs to always return "true". This patch makes that be so. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1267135607-7056-2-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Introduce lockdep-based checking to RCU read-side primitivesPaul E. McKenney2010-02-251-0/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Inspection is proving insufficient to catch all RCU misuses, which is understandable given that rcu_dereference() might be protected by any of four different flavors of RCU (RCU, RCU-bh, RCU-sched, and SRCU), and might also/instead be protected by any of a number of locking primitives. It is therefore time to enlist the aid of lockdep. This set of patches is inspired by earlier work by Peter Zijlstra and Thomas Gleixner, and takes the following approach: o Set up separate lockdep classes for RCU, RCU-bh, and RCU-sched. o Set up separate lockdep classes for each instance of SRCU. o Create primitives that check for being in an RCU read-side critical section. These return exact answers if lockdep is fully enabled, but if unsure, report being in an RCU read-side critical section. (We want to avoid false positives!) The primitives are: For RCU: rcu_read_lock_held(void) For RCU-bh: rcu_read_lock_bh_held(void) For RCU-sched: rcu_read_lock_sched_held(void) For SRCU: srcu_read_lock_held(struct srcu_struct *sp) o Add rcu_dereference_check(), which takes a second argument in which one places a boolean expression based on the above primitives and/or lockdep_is_held(). o A new kernel configuration parameter, CONFIG_PROVE_RCU, enables rcu_dereference_check(). This depends on CONFIG_PROVE_LOCKING, and should be quite helpful during the transition period while CONFIG_PROVE_RCU-unaware patches are in flight. The existing rcu_dereference() primitive does no checking, but upcoming patches will change that. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-1-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Re-arrange code to reduce #ifdef painPaul E. McKenney2009-11-221-104/+0
| | | | | | | | | | | | | | | | | | | | | | | Remove #ifdefs from kernel/rcupdate.c and include/linux/rcupdate.h by moving code to include/linux/rcutiny.h, include/linux/rcutree.h, and kernel/rcutree.c. Also remove some definitions that are no longer used. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1258908830885-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate unneeded function wrappingPaul E. McKenney2009-11-221-22/+0
| | | | | | | | | | | | | | | | | | | | | | | | | The functions rcu_init() is a wrapper for __rcu_init(), and also sets up the CPU-hotplug notifier for rcu_barrier_cpu_hotplug(). But TINY_RCU doesn't need CPU-hotplug notification, and the rcu_barrier_cpu_hotplug() is a simple wrapper for rcu_cpu_notify(). So push rcu_init() out to kernel/rcutree.c and kernel/rcutiny.c and get rid of the wrapper function rcu_barrier_cpu_hotplug(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12589088302320-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: "Tiny RCU", The Bloatwatch EditionPaul E. McKenney2009-10-261-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch is a version of RCU designed for !SMP provided for a small-footprint RCU implementation. In particular, the implementation of synchronize_rcu() is extremely lightweight and high performance. It passes rcutorture testing in each of the four relevant configurations (combinations of NO_HZ and PREEMPT) on x86. This saves about 1K bytes compared to old Classic RCU (which is no longer in mainline), and more than three kilobytes compared to Hierarchical RCU (updated to 2.6.30): CONFIG_TREE_RCU: text data bss dec filename 183 4 0 187 kernel/rcupdate.o 2783 520 36 3339 kernel/rcutree.o 3526 Total (vs 4565 for v7) CONFIG_TREE_PREEMPT_RCU: text data bss dec filename 263 4 0 267 kernel/rcupdate.o 4594 776 52 5422 kernel/rcutree.o 5689 Total (6155 for v7) CONFIG_TINY_RCU: text data bss dec filename 96 4 0 100 kernel/rcupdate.o 734 24 0 758 kernel/rcutiny.o 858 Total (vs 848 for v7) The above is for x86. Your mileage may vary on other platforms. Further compression is possible, but is being procrastinated. Changes from v7 (http://lkml.org/lkml/2009/10/9/388) o Apply Lai Jiangshan's review comments (aside from might_sleep() in synchronize_sched(), which is covered by SMP builds). o Fix up expedited primitives. Changes from v6 (http://lkml.org/lkml/2009/9/23/293). o Forward ported to put it into the 2.6.33 stream. o Added lockdep support. o Make lightweight rcu_barrier. Changes from v5 (http://lkml.org/lkml/2009/6/23/12). o Ported to latest pre-2.6.32 merge window kernel. - Renamed rcu_qsctr_inc() to rcu_sched_qs(). - Renamed rcu_bh_qsctr_inc() to rcu_bh_qs(). - Provided trivial rcu_cpu_notify(). - Provided trivial exit_rcu(). - Provided trivial rcu_needs_cpu(). - Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h. o Removed the dependence on EMBEDDED, with a view to making TINY_RCU default for !SMP at some time in the future. o Added (trivial) support for expedited grace periods. Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include: o Squeeze the size down a bit further by removing the ->completed field from struct rcu_ctrlblk. o This permits synchronize_rcu() to become the empty function. Previous concerns about rcutorture were unfounded, as rcutorture correctly handles a constant value from rcu_batches_completed() and rcu_batches_completed_bh(). Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include: o Changed rcu_batches_completed(), rcu_batches_completed_bh() rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and rcu_nmi_exit(), to be static inlines, as suggested by David Howells. Doing this saves about 100 bytes from rcutiny.o. (The numbers between v3 and this v4 of the patch are not directly comparable, since they are against different versions of Linux.) Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include: o Fix whitespace issues. o Change short-circuit "||" operator to instead be "+" in order to fix performance bug noted by "kraai" on LWN. (http://lwn.net/Articles/324348/) Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include: o This version depends on EMBEDDED as well as !SMP, as suggested by Ingo. o Updated rcu_needs_cpu() to unconditionally return zero, permitting the CPU to enter dynticks-idle mode at any time. This works because callbacks can be invoked upon entry to dynticks-idle mode. o Paul is now OK with this being included, based on a poll at the Kernel Miniconf at linux.conf.au, where about ten people said that they cared about saving 900 bytes on single-CPU systems. o Applies to both mainline and tip/core/rcu. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: avi@redhat.com Cc: mtosatti@redhat.com LKML-Reference: <12565226351355-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Move rcu_barrier() to rcutreePaul E. McKenney2009-10-071-119/+1
| | | | | | | | | | | | | | | | | | | | | | | | Move the existing rcu_barrier() implementation to rcutree.c, consistent with the fact that the rcu_barrier() implementation is tied quite tightly to the RCU implementation. This opens the way to simplify and fix rcutree.c's rcu_barrier() implementation in a later patch. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12548908982563-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Replace the rcu_barrier enum with pointer to call_rcu*() functionPaul E. McKenney2009-10-051-22/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_barrier enum causes several problems: (1) you have to define the enum somewhere, and there is no convenient place, (2) the difference between TREE_RCU and TREE_PREEMPT_RCU causes problems when you need to map from rcu_barrier enum to struct rcu_state, (3) the switch statement are large, and (4) TINY_RCU really needs a different rcu_barrier() than do the treercu implementations. So replace it with a functionally equivalent but cleaner function pointer abstraction. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12541998232366-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix rcu_lock_map build failure on CONFIG_PROVE_LOCKING=yPaul E. McKenney2009-10-051-0/+7
| | | | | | | | | Move the rcu_lock_map definition from rcutree.c to rcupdate.c so that TINY_RCU can use lockdep. Reported-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Clean up code to address Ingo's checkpatch feedbackPaul E. McKenney2009-09-231-3/+0
| | | | | | | | | | | | | | | | | | | Move declarations and update storage classes to make checkpatch happy. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246441701-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix whitespace inconsistenciesPaul E. McKenney2009-09-191-2/+2
| | | | | | | | | | | | | | | | | | | | Fix a number of whitespace ^Ierrors in the include/linux/rcu* and the kernel/rcu* files. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <20090918172819.GA24405@linux.vnet.ibm.com> [ did more checkpatch fixlets ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix synchronize_rcu() for TREE_PREEMPT_RCUPaul E. McKenney2009-09-181-1/+43
| | | | | | | | | | | | | | | | | | | | | | | The redirection of synchronize_sched() to synchronize_rcu() was appropriate for TREE_RCU, but not for TREE_PREEMPT_RCU. Fix this by creating an underlying synchronize_sched(). TREE_RCU then redirects synchronize_rcu() to synchronize_sched(), while TREE_PREEMPT_RCU has its own version of synchronize_rcu(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <12528585111916-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Delay rcu_barrier() wait until beginning of next CPU-hotunplug operation.Paul E. McKenney2009-08-191-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Ingo Molnar reported this lockup: [ 200.380003] Hangcheck: hangcheck value past margin! [ 248.192003] INFO: task S99local:2974 blocked for more than 120 seconds. [ 248.194532] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 248.202330] S99local D 0000000c 6256 2974 2687 0x00000000 [ 248.208929] 9c7ebe90 00000086 6b67ef8b 0000000c 9f25a610 81a69869 00000001 820b6990 [ 248.216123] 820b6990 820b6990 9c6e4c20 9c6e4eb4 82c78990 00000000 6b993559 0000000c [ 248.220616] 9c7ebe90 8105f22a 9c6e4eb4 9c6e4c20 00000001 9c7ebe98 9c7ebeb4 81a65cb3 [ 248.229990] Call Trace: [ 248.234049] [<81a69869>] ? _spin_unlock_irqrestore+0x22/0x37 [ 248.239769] [<8105f22a>] ? prepare_to_wait+0x48/0x4e [ 248.244796] [<81a65cb3>] rcu_barrier_cpu_hotplug+0xaa/0xc9 [ 248.250343] [<8105f029>] ? autoremove_wake_function+0x0/0x38 [ 248.256063] [<81062cf2>] notifier_call_chain+0x49/0x71 [ 248.261263] [<81062da0>] raw_notifier_call_chain+0x11/0x13 [ 248.266809] [<81a0b475>] _cpu_down+0x272/0x288 [ 248.271316] [<81a0b4d5>] cpu_down+0x4a/0xa2 [ 248.275563] [<81a0c48a>] store_online+0x2a/0x5e [ 248.280156] [<81a0c460>] ? store_online+0x0/0x5e [ 248.284836] [<814ddc35>] sysdev_store+0x20/0x28 [ 248.289429] [<8112e403>] sysfs_write_file+0xb8/0xe3 [ 248.294369] [<8112e34b>] ? sysfs_write_file+0x0/0xe3 [ 248.299396] [<810e4c8f>] vfs_write+0x91/0x120 [ 248.303817] [<810e4dc1>] sys_write+0x40/0x65 [ 248.308150] [<81002d73>] sysenter_do_call+0x12/0x28 This change moves an RCU grace period delay off of the critical path for CPU-hotunplug operations. Since RCU callback migration is only performed on CPU-hotunplug operations, and since the rcu_barrier() race is provoked only by consecutive CPU-hotunplug operations, it is not necessary to delay the end of a given CPU-hotunplug operation. We can instead choose to delay the beginning of the next CPU-hotunplug operation. Reported-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josht@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: hugh.dickins@tiscali.co.uk Cc: benh@kernel.crashing.org LKML-Reference: <20090819060614.GA14383@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Simplify RCU CPU-hotplug notificationPaul E. McKenney2009-08-151-1/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | Use the new cpu_notifier() API to simplify RCU's CPU-hotplug notifiers, collapsing down to a single such notifier. This makes it trivial to provide the notifier-ordering guarantee that rcu_barrier() depends on. Also remove redundant open_softirq() calls from Hierarchical RCU notifier. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: josht@linux.vnet.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: hugh.dickins@tiscali.co.uk Cc: benh@kernel.crashing.org LKML-Reference: <12503552312510-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Add synchronize_sched_expedited() primitivePaul E. McKenney2009-07-031-0/+25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This adds the synchronize_sched_expedited() primitive that implements the "big hammer" expedited RCU grace periods. This primitive is placed in kernel/sched.c rather than kernel/rcupdate.c due to its need to interact closely with the migration_thread() kthread. The idea is to wake up this kthread with req->task set to NULL, in response to which the kthread reports the quiescent state resulting from the kthread having been scheduled. Because this patch needs to fallback to the slow versions of the primitives in response to some races with CPU onlining and offlining, a new synchronize_rcu_bh() primitive is added as well. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org Cc: davem@davemloft.net Cc: dada1@cosmosbay.com Cc: zbr@ioremap.net Cc: jeff.chua.linux@gmail.com Cc: paulus@samba.org Cc: laijs@cn.fujitsu.com Cc: jengelh@medozas.de Cc: r000n@r000n.net Cc: benh@kernel.crashing.org Cc: mathieu.desnoyers@polymtl.ca LKML-Reference: <12459460982947-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* RCU: Don't try and predeclare inline funcs as it upsets some versions of gccDavid Howells2009-04-151-10/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Don't try and predeclare inline funcs like this: static inline void wait_migrated_callbacks(void) ... static void _rcu_barrier(enum rcu_barrier type) { ... wait_migrated_callbacks(); } ... static inline void wait_migrated_callbacks(void) { wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count)); } as it upsets some versions of gcc under some circumstances: kernel/rcupdate.c: In function `_rcu_barrier': kernel/rcupdate.c:125: sorry, unimplemented: inlining failed in call to 'wait_migrated_callbacks': function body not available kernel/rcupdate.c:152: sorry, unimplemented: called from here This can be dealt with by simply putting the static variables (rcu_migrate_*) at the top, and moving the implementation of the function up so that it replaces its forward declaration. Signed-off-by: David Howells <dhowells@redhat.com> Cc: Dipankar Sarma <dipankar@in.ibm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* rcu: rcu_barrier VS cpu_hotplug: Ensure callbacks in dead cpu are migrated ↵Lai Jiangshan2009-03-311-0/+44
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | to online cpu cpu hotplug may happen asynchronously, some rcu callbacks are maybe still on dead cpu, rcu_barrier() also needs to wait for these rcu callbacks to complete, so we must ensure callbacks in dead cpu are migrated to online cpu. Paul E. McKenney's review: Good stuff, Lai!!! Simpler than any of the approaches that I was considering, and, better yet, independent of the underlying RCU implementation!!! I was initially worried that wake_up() might wake only one of two possible wait_event()s, namely rcu_barrier() and the CPU_POST_DEAD code, but the fact that wait_event() clears WQ_FLAG_EXCLUSIVE avoids that issue. I was also worried about the fact that different RCU implementations have different mappings of call_rcu(), call_rcu_bh(), and call_rcu_sched(), but this is OK as well because we just get an extra (harmless) callback in the case that they map together (for example, Classic RCU has call_rcu_sched() mapping to call_rcu()). Overlap of CPU-hotplug operations is prevented by cpu_add_remove_lock, and any stray callbacks that arrive (for example, from irq handlers running on the dying CPU) either are ahead of the CPU_DYING callbacks on the one hand (and thus accounted for), or happened after the rcu_barrier() started on the other (and thus don't need to be accounted for). Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> LKML-Reference: <49C36476.1010400@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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