From c78416d122243c92992a1d1063f17ddd0bc80e6c Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Sun, 19 Sep 2021 22:20:30 -0700
Subject: [PATCH] locking/rwbase: Optimize rwbase_read_trylock
Git-commit: c78416d122243c92992a1d1063f17ddd0bc80e6c
Patch-mainline: v5.16-rc1
References: bsc#1190137 bsc#1189998
Instead of a full barrier around the Rmw insn, micro-optimize
for weakly ordered archs such that we only provide the required
ACQUIRE semantics when taking the read lock.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@stgolabs.net
---
kernel/locking/rwbase_rt.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 15c81100f0e2..6fd3162e4098 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -59,8 +59,7 @@ static __always_inline int rwbase_read_trylock(struct rwbase_rt *rwb)
* set.
*/
for (r = atomic_read(&rwb->readers); r < 0;) {
- /* Fully-ordered if cmpxchg() succeeds, provides ACQUIRE */
- if (likely(atomic_try_cmpxchg(&rwb->readers, &r, r + 1)))
+ if (likely(atomic_try_cmpxchg_acquire(&rwb->readers, &r, r + 1)))
return 1;
}
return 0;
@@ -187,7 +186,7 @@ static inline void __rwbase_write_unlock(struct rwbase_rt *rwb, int bias,
/*
* _release() is needed in case that reader is in fast path, pairing
- * with atomic_try_cmpxchg() in rwbase_read_trylock(), provides RELEASE
+ * with atomic_try_cmpxchg_acquire() in rwbase_read_trylock().
*/
(void)atomic_add_return_release(READER_BIAS - bias, &rwb->readers);
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
--
2.26.2