From: Peter Zijlstra <peterz@infradead.org>
To: peterz@infradead.org, mingo@kernel.org, will@kernel.org
Cc: oleg@redhat.com, tglx@linutronix.de,
linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
juri.lelli@redhat.com, williams@redhat.com, bristot@redhat.com,
longman@redhat.com, dave@stgolabs.net, jack@suse.com
Subject: [PATCH 4/5] locking/percpu-rwsem: Extract __percpu_down_read_trylock()
Date: Wed, 13 Nov 2019 11:21:19 +0100 [thread overview]
Message-ID: <20191113102855.868390100@infradead.org> (raw)
In-Reply-To: 20191113102115.116470462@infradead.org
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;
next prev parent reply other threads:[~2019-11-13 10:29 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 10:21 [PATCH 0/5] locking: Percpu-rwsem rewrite Peter Zijlstra
2019-11-13 10:21 ` [PATCH 1/5] locking/percpu-rwsem, lockdep: Make percpu-rwsem use its own lockdep_map Peter Zijlstra
2019-11-15 20:39 ` Davidlohr Bueso
2020-01-08 1:33 ` [PATCH] locking/percpu-rwsem: Add might_sleep() for writer locking Davidlohr Bueso
2020-01-08 1:33 ` Davidlohr Bueso
2020-02-11 12:48 ` [tip: locking/core] " tip-bot2 for Davidlohr Bueso
2019-11-13 10:21 ` [PATCH 2/5] locking/percpu-rwsem: Convert to bool Peter Zijlstra
2019-11-13 10:21 ` [PATCH 3/5] locking/percpu-rwsem: Move __this_cpu_inc() into the slowpath Peter Zijlstra
2019-11-13 10:21 ` Peter Zijlstra [this message]
2019-11-18 16:28 ` [PATCH 4/5] locking/percpu-rwsem: Extract __percpu_down_read_trylock() Oleg Nesterov
2019-11-13 10:21 ` [PATCH 5/5] locking/percpu-rwsem: Remove the embedded rwsem Peter Zijlstra
2019-11-18 19:53 ` Davidlohr Bueso
2019-11-18 23:19 ` Davidlohr Bueso
2019-12-17 10:45 ` Peter Zijlstra
2019-12-17 10:35 ` Peter Zijlstra
2019-11-18 21:52 ` Waiman Long
2019-12-17 10:28 ` Peter Zijlstra
2019-11-19 13:50 ` Waiman Long
2019-11-19 15:58 ` Oleg Nesterov
2019-11-19 16:28 ` Waiman Long
2019-12-17 10:26 ` Peter Zijlstra
2019-12-17 10:28 ` Peter Zijlstra
2019-11-15 17:14 ` [PATCH 0/5] locking: Percpu-rwsem rewrite Juri Lelli
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