Messages in this thread Patch in this message | | | Date | Wed, 13 Nov 2019 11:21:19 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 4/5] locking/percpu-rwsem: Extract __percpu_down_read_trylock() |
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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> --- kernel/locking/percpu-rwsem.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-)
--- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -45,7 +45,7 @@ void percpu_free_rwsem(struct percpu_rw_ } 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); @@ -70,14 +70,21 @@ bool __percpu_down_read(struct percpu_rw * If !readers_block the critical section starts here, matched by the * release in percpu_up_write(). */ - if (likely(!smp_load_acquire(&sem->readers_block))) + if (likely(!atomic_read_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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