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2010-08-20rcu: Upgrade srcu_read_lock() docbook about SRCU grace periodsPaul E. McKenney
It is illegal to wait for an SRCU grace period while within the corresponding flavor of SRCU read-side critical section. Therefore, this commit updates the srcu_read_lock() docbook accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-08-19rcu: define __rcu address space modifier for sparsePaul E. McKenney
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>
2010-05-10rcu: make SRCU usable in modulesPaul E. McKenney
Add a #include for mutex.h to allow SRCU to be more easily used in kernel modules. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-05-10rcu: Fix bogus CONFIG_PROVE_LOCKING in comments to reflect reality.Paul E. McKenney
It is CONFIG_DEBUG_LOCK_ALLOC rather than CONFIG_PROVE_LOCKING, so fix it. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-03-03Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu: percpu: add __percpu sparse annotations to what's left percpu: add __percpu sparse annotations to fs percpu: add __percpu sparse annotations to core kernel subsystems local_t: Remove leftover local.h this_cpu: Remove pageset_notifier this_cpu: Page allocator conversion percpu, x86: Generic inc / dec percpu instructions local_t: Move local.h include to ringbuffer.c and ring_buffer_benchmark.c module: Use this_cpu_xx to dynamically allocate counters local_t: Remove cpu_local_xx macros percpu: refactor the code in pcpu_[de]populate_chunk() percpu: remove compile warnings caused by __verify_pcpu_ptr() percpu: make accessors check for percpu pointer in sparse percpu: add __percpu for sparse. percpu: make access macros universal percpu: remove per_cpu__ prefix.
2010-02-25rcu: Add lockdep-enabled variants of rcu_dereference()Paul E. McKenney
Make rcu_dereference() check for being in an RCU read-side critical section, and create rcu_dereference_bh(), rcu_dereference_sched(), and srcu_dereference() to check for the other flavors of RCU. Also create rcu_dereference_raw() to avoid checking, and make rcu_dereference_check() use rcu_dereference_raw(). Acked-by: Eric Dumazet <eric.dumazet@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 LKML-Reference: <1266887105-1528-2-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-02-25rcu: Introduce lockdep-based checking to RCU read-side primitivesPaul E. McKenney
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>
2010-02-17percpu: add __percpu sparse annotations to core kernel subsystemsTejun Heo
Add __percpu sparse annotations to core subsystems. These annotations are to make sparse consider percpu variables to be in a different address space and warn if accessed without going through percpu accessors. This patch doesn't affect normal builds. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Christoph Lameter <cl@linux-foundation.org> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-mm@kvack.org Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Dipankar Sarma <dipankar@in.ibm.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Eric Biederman <ebiederm@xmission.com>
2009-10-26rcu: Add synchronize_srcu_expedited()Paul E. McKenney
This patch creates a synchronize_srcu_expedited() that uses synchronize_sched_expedited() where synchronize_srcu() uses synchronize_sched(). The synchronize_srcu() and synchronize_srcu_expedited() functions become one-liners that pass synchronize_sched() or synchronize_sched_expedited(), repectively, to a new __synchronize_srcu() function. While in the file, move the EXPORT_SYMBOL_GPL()s to immediately follow the corresponding functions. Requested-by: Avi Kivity <avi@redhat.com> Tested-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.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: dhowells@redhat.com Cc: avi@redhat.com LKML-Reference: <12565226354038-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-10-04[PATCH] SRCU: report out-of-memory errorsAlan Stern
Currently the init_srcu_struct() routine has no way to report out-of-memory errors. This patch (as761) makes it return -ENOMEM when the per-cpu data allocation fails. The patch also makes srcu_init_notifier_head() report a BUG if a notifier head can't be initialized. Perhaps it should return -ENOMEM instead, but in the most likely cases where this might occur I don't think any recovery is possible. Notifier chains generally are not created dynamically. [akpm@osdl.org: avoid statement-with-side-effect in macro] Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-04[PATCH] Add SRCU-based notifier chainsAlan Stern
This patch (as751) adds a new type of notifier chain, based on the SRCU (Sleepable Read-Copy Update) primitives recently added to the kernel. An SRCU notifier chain is much like a blocking notifier chain, in that it must be called in process context and its callout routines are allowed to sleep. The difference is that the chain's links are protected by the SRCU mechanism rather than by an rw-semaphore, so calling the chain has extremely low overhead: no memory barriers and no cache-line bouncing. On the other hand, unregistering from the chain is expensive and the chain head requires special runtime initialization (plus cleanup if it is to be deallocated). SRCU notifiers are appropriate for notifiers that will be called very frequently and for which unregistration occurs very seldom. The proposed "task notifier" scheme qualifies, as may some of the network notifiers. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Acked-by: Chandra Seetharaman <sekharan@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-04[PATCH] srcu-3: RCU variant permitting read-side blockingPaul E. McKenney
Updated patch adding a variant of RCU that permits sleeping in read-side critical sections. SRCU is as follows: o Each use of SRCU creates its own srcu_struct, and each srcu_struct has its own set of grace periods. This is critical, as it prevents one subsystem with a blocking reader from holding up SRCU grace periods for other subsystems. o The SRCU primitives (srcu_read_lock(), srcu_read_unlock(), and synchronize_srcu()) all take a pointer to a srcu_struct. o The SRCU primitives must be called from process context. o srcu_read_lock() returns an int that must be passed to the matching srcu_read_unlock(). Realtime RCU avoids the need for this by storing the state in the task struct, but SRCU needs to allow a given code path to pass through multiple SRCU domains -- storing state in the task struct would therefore require either arbitrary space in the task struct or arbitrary limits on SRCU nesting. So I kicked the state-storage problem up to the caller. Of course, it is not permitted to call synchronize_srcu() while in an SRCU read-side critical section. o There is no call_srcu(). It would not be hard to implement one, but it seems like too easy a way to OOM the system. (Hey, we have enough trouble with call_rcu(), which does -not- permit readers to sleep!!!) So, if you want it, please tell me why... [josht@us.ibm.com: sparse notation] Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Josh Triplett <josh@freedesktop.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>