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Subject[tip: locking/core] locking/percpu-rwsem: Extract __percpu_down_read_trylock()
The following commit has been merged into the locking/core branch of tip:

Commit-ID: 75ff64572e497578e238fefbdff221c96f29067a
Gitweb: https://git.kernel.org/tip/75ff64572e497578e238fefbdff221c96f29067a
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 31 Oct 2019 12:34:23 +01:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 11 Feb 2020 13:10:55 +01:00

locking/percpu-rwsem: Extract __percpu_down_read_trylock()

In preparation for removing the embedded rwsem and building a custom
lock, extract the read-trylock primitive.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.098485539@infradead.org
---
kernel/locking/percpu-rwsem.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index becf925..b155e8e 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -45,7 +45,7 @@ void percpu_free_rwsem(struct percpu_rw_semaphore *sem)
}
EXPORT_SYMBOL_GPL(percpu_free_rwsem);

-bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
+static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
__this_cpu_inc(*sem->read_count);

@@ -73,11 +73,18 @@ bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
if (likely(!smp_load_acquire(&sem->readers_block)))
return true;

- /*
- * Per the above comment; we still have preemption disabled and
- * will thus decrement on the same CPU as we incremented.
- */
- __percpu_up_read(sem);
+ __this_cpu_dec(*sem->read_count);
+
+ /* Prod writer to re-evaluate readers_active_check() */
+ rcuwait_wake_up(&sem->writer);
+
+ return false;
+}
+
+bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
+{
+ if (__percpu_down_read_trylock(sem))
+ return true;

if (try)
return false;
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