locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count

hulk inclusion
category: bugfix
bugzilla: NA
CVE: NA

---------------------------

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.

Fixing 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: 70fe2f48 ("aio: fix freeze protection of aio writes")
Signed-off-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200915140750.137881-1-houtao1@huawei.comSigned-off-by: NZhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/percpu-rwsem.h

@@ -44,7 +44,7 @@ static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *
 	 * and that one the synchronize_sched() is done, the writer will see
 	 * anything we did within this RCU-sched read-size critical section.
 	 */
-	__this_cpu_inc(*sem->read_count);
+	this_cpu_inc(*sem->read_count);
 	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
 		__percpu_down_read(sem, false); /* Unconditional memory barrier */
 	barrier();
@@ -68,7 +68,7 @@ static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 	/*
 	 * Same as in percpu_down_read().
 	 */
-	__this_cpu_inc(*sem->read_count);
+	this_cpu_inc(*sem->read_count);
 	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
 		ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
 	preempt_enable();
@@ -94,7 +94,7 @@ static inline void percpu_up_read_preempt_enable(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
 		__percpu_up_read(sem); /* Unconditional memory barrier */
 	preempt_enable();

kernel/locking/percpu-rwsem.c

@@ -99,7 +99,7 @@ void __percpu_up_read(struct percpu_rw_semaphore *sem)
 	 * 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);
 
 	/* Prod writer to recheck readers_active */
 	rcuwait_wake_up(&sem->writer);