user/sven/linux.git/kernel/rcu/sync.c, branch v6.1.162

rcu_sync: Fix comment to properly reflect rcu_sync_exit() behavior

2022-04-20T23:51:11Z

The rcu_sync_enter() function is used by updaters to force RCU readers (e.g. percpu-rwsem) to use their slow paths during an update. This is accomplished by setting the ->gp_state of the rcu_sync structure to GP_ENTER. In the case of percpu-rwsem, the readers' slow path waits on a semaphore instead of just incrementing a reader count. Each updater invokes the rcu_sync_exit() function to signal to readers that they may again take their fastpaths. The rcu_sync_exit() function sets the ->gp_state of the rcu_sync structure to GP_EXIT, and if all goes well, after a grace period the ->gp_state reverts back to GP_IDLE. Unfortunately, the rcu_sync_enter() function currently has a comment incorrectly stating that rcu_sync_exit() (by an updater) will re-enable reader "slowpaths". This patch changes the comment to state that this function re-enables reader fastpaths. Signed-off-by: David Vernet Signed-off-by: Paul E. McKenney

rcu: Fix various typos in comments

2021-05-12T19:11:05Z

Fix ~12 single-word typos in RCU code comments. [ paulmck: Apply feedback from Randy Dunlap. ] Reviewed-by: Randy Dunlap Signed-off-by: Ingo Molnar Signed-off-by: Paul E. McKenney

rcu/sync: Simplify the state machine

2019-05-28T16:05:23Z

With this patch rcu_sync has a single state variable and the transition rules become really simple: GP_IDLE - owned by the first rcu_sync_enter() which moves it to GP_ENTER - owned by rcu-callback which moves it to GP_PASSED - owned by the last rcu_sync_exit() which moves it to GP_EXIT - and this is the only "nontrivial" state. rcu-callback moves it back to GP_IDLE unless another enter() comes before a GP pass. If rcu-callback is invoked before the next rcu_sync_exit() it must see gp_count incremented by that enter() and set GP_PASSED. Otherwise, if the next rcu_sync_exit() wins the race, it will move it to GP_REPLAY - owned by rcu-callback which moves it to GP_EXIT Signed-off-by: Oleg Nesterov [ paulmck: While here, apply READ_ONCE() and WRITE_ONCE() to ->gp_state. ] [ paulmck: Tweaks to make htmldocs happy. (Reported by kbuild test robot.) ] Signed-off-by: Paul E. McKenney

rcu/sync: Kill rcu_sync_type/gp_type

2019-05-28T16:05:23Z

Now that the RCU flavors have been consolidated, rcu_sync_type makes no sense because none of internal update functions aside from .held() depend on gp_type. This commit therefore removes this field and consolidates the relevant code. Signed-off-by: Oleg Nesterov [ paulmck: Added RCU and RCU-bh checks to rcu_sync_is_idle(). ] [ paulmck: And applied subsequent feedback from Oleg Nesterov. ] Signed-off-by: Paul E. McKenney

rcu/sync: Convert to SPDX license identifier

2019-02-09T16:43:59Z

Replace the license boiler plate with a SPDX license identifier. Signed-off-by: Paul E. McKenney Reviewed-by: Thomas Gleixner

Merge branches 'bug.2018.11.12a', 'consolidate.2018.12.01a', 'doc.2018.11.12a', 'fixes.2018.11.12a', 'initrd.2018.11.08b', 'sil.2018.11.12a' and 'srcu.2018.11.27a' into HEAD

2018-12-01T20:43:16Z

bug.2018.11.12a: Get rid of BUG_ON() and friends consolidate.2018.12.01a: Continued RCU flavor-consolidation cleanup doc.2018.11.12a: Documentation updates fixes.2018.11.12a: Miscellaneous fixes initrd.2018.11.08b: Automate creation of rcutorture initrd sil.2018.11.12a: Remove more spin_unlock_wait() calls

rcu: Consolidate the RCU update functions invoked by sync.c

2018-11-09T05:43:20Z

This commit retains all the various gp_ops[] entries, but makes their update functions all be synchronize_rcu(), call_rcu() and rcu_barrier(). The read-side checks remain consistent with the various RCU flavors, which still exist on the read side. Signed-off-by: Paul E. McKenney Cc: Oleg Nesterov Cc: Peter Zijlstra

rcu: Eliminate BUG_ON() for sync.c

2018-11-09T05:41:57Z

The sync.c file has a number of calls to BUG_ON(), which panics the kernel, which is not a good strategy for devices (like embedded) that don't have a way to capture console output. This commit therefore changes these BUG_ON() calls to WARN_ON_ONCE(), but does so quite naively. Reported-by: Linus Torvalds Signed-off-by: Paul E. McKenney Acked-by: Oleg Nesterov Cc: Peter Zijlstra

doc: Fix various RCU docbook comment-header problems

2017-10-20T02:26:11Z

Because many of RCU's files have not been included into docbook, a number of errors have accumulated. This commit fixes them. Signed-off-by: Paul E. McKenney Signed-off-by: Linus Torvalds

locking, rcu, cgroup: Avoid synchronize_sched() in __cgroup_procs_write()

2016-08-18T13:36:59Z

The current percpu-rwsem read side is entirely free of serializing insns at the cost of having a synchronize_sched() in the write path. The latency of the synchronize_sched() is too high for cgroups. The commit 1ed1328792ff talks about the write path being a fairly cold path but this is not the case for Android which moves task to the foreground cgroup and back around binder IPC calls from foreground processes to background processes, so it is significantly hotter than human initiated operations. Switch cgroup_threadgroup_rwsem into the slow mode for now to avoid the problem, hopefully it should not be that slow after another commit: 80127a39681b ("locking/percpu-rwsem: Optimize readers and reduce global impact"). We could just add rcu_sync_enter() into cgroup_init() but we do not want another synchronize_sched() at boot time, so this patch adds the new helper which doesn't block but currently can only be called before the first use. Reported-by: John Stultz Reported-by: Dmitry Shmidt Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Colin Cross Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rom Lemarchand Cc: Tejun Heo Cc: Thomas Gleixner Cc: Todd Kjos Link: http://lkml.kernel.org/r/20160811165413.GA22807@redhat.com Signed-off-by: Ingo Molnar