The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: e6b1a44eccfcab5e5e280be376f65478c3b2c7a2 Gitweb: https://git.kernel.org/tip/e6b1a44eccfcab5e5e280be376f65478c3b2c7a2 Author: Hou Tao <hout...@huawei.com> AuthorDate: Tue, 15 Sep 2020 22:07:50 +08:00 Committer: Peter Zijlstra <pet...@infradead.org> CommitterDate: Wed, 16 Sep 2020 16:26:56 +02:00 locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count The __this_cpu*() accessors are (in general) IRQ-unsafe which, given that percpu-rwsem is a blocking primitive, should be just fine. However, file_end_write() is used from IRQ context and will cause load-store issues on architectures where the per-cpu accessors are not natively irq-safe. Fix it by using the IRQ-safe this_cpu_*() for operations on read_count. This will generate more expensive code on a number of platforms, which might cause a performance regression for some of the other percpu-rwsem users. If any such is reported, we can consider alternative solutions. Fixes: 70fe2f48152e ("aio: fix freeze protection of aio writes") Signed-off-by: Hou Tao <hout...@huawei.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Acked-by: Will Deacon <w...@kernel.org> Acked-by: Oleg Nesterov <o...@redhat.com> Link: https://lkml.kernel.org/r/20200915140750.137881-1-hout...@huawei.com --- include/linux/percpu-rwsem.h | 8 ++++---- kernel/locking/percpu-rwsem.c | 4 ++-- 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h index 5e033fe..5fda40f 100644 --- a/include/linux/percpu-rwsem.h +++ b/include/linux/percpu-rwsem.h @@ -60,7 +60,7 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem) * anything we did within this RCU-sched read-size critical section. */ if (likely(rcu_sync_is_idle(&sem->rss))) - __this_cpu_inc(*sem->read_count); + this_cpu_inc(*sem->read_count); else __percpu_down_read(sem, false); /* Unconditional memory barrier */ /* @@ -79,7 +79,7 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem) * Same as in percpu_down_read(). */ if (likely(rcu_sync_is_idle(&sem->rss))) - __this_cpu_inc(*sem->read_count); + this_cpu_inc(*sem->read_count); else ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */ preempt_enable(); @@ -103,7 +103,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem) * Same as in percpu_down_read(). */ if (likely(rcu_sync_is_idle(&sem->rss))) { - __this_cpu_dec(*sem->read_count); + this_cpu_dec(*sem->read_count); } else { /* * slowpath; reader will only ever wake a single blocked @@ -115,7 +115,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem) * aggregate zero, as that is the only time it matters) they * will also see our critical section. */ - __this_cpu_dec(*sem->read_count); + this_cpu_dec(*sem->read_count); rcuwait_wake_up(&sem->writer); } preempt_enable(); diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index 8bbafe3..70a32a5 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -45,7 +45,7 @@ EXPORT_SYMBOL_GPL(percpu_free_rwsem); static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem) { - __this_cpu_inc(*sem->read_count); + this_cpu_inc(*sem->read_count); /* * Due to having preemption disabled the decrement happens on @@ -71,7 +71,7 @@ static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem) if (likely(!atomic_read_acquire(&sem->block))) return true; - __this_cpu_dec(*sem->read_count); + this_cpu_dec(*sem->read_count); /* Prod writer to re-evaluate readers_active_check() */ rcuwait_wake_up(&sem->writer);
