From 75ff64572e497578e238fefbdff221c96f29067a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 31 Oct 2019 12:34:23 +0100 Subject: [PATCH] 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) Signed-off-by: Ingo Molnar Reviewed-by: Davidlohr Bueso Acked-by: Will Deacon Acked-by: Waiman Long Tested-by: Juri Lelli 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 becf925b27b5..b155e8e7ac39 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; -- 2.11.0