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From 99143f82a255e7f054bead8443462fae76dd829e Mon Sep 17 00:00:00 2001
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From: Peter Zijlstra <peterz@infradead.org>
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Davidlohr Bueso |
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Date: Thu, 18 Jul 2019 14:56:17 +0200
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Subject: [PATCH] lcoking/rwsem: Add missing ACQUIRE to read_slowpath sleep
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loop
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Git-commit: 99143f82a255e7f054bead8443462fae76dd829e
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Patch-mainline: v5.3-rc1
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References: bsc#1050549
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While reviewing another read_slowpath patch, both Will and I noticed
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another missing ACQUIRE, namely:
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X = 0;
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CPU0 CPU1
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rwsem_down_read()
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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X = 1;
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rwsem_up_write();
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rwsem_mark_wake()
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atomic_long_add(adjustment, &sem->count);
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smp_store_release(&waiter->task, NULL);
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if (!waiter.task)
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break;
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...
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}
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r = X;
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Allows 'r == 0'.
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Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Reported-by: Will Deacon <will@kernel.org>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Acked-by: Will Deacon <will@kernel.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
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---
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kernel/locking/rwsem-xadd.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
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index 7d29e15d8f44..cca18df9925d 100644
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--- a/kernel/locking/rwsem-xadd.c
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+++ b/kernel/locking/rwsem-xadd.c
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@@ -277,8 +277,10 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
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/* wait to be given the lock */
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while (true) {
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set_current_state(state);
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- if (!waiter.task)
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+ if (!smp_load_acquire(&waiter.task)) {
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+ /* Orders against rwsem_mark_wake()'s smp_store_release() */
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break;
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+ }
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if (signal_pending_state(state, current)) {
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raw_spin_lock_irq(&sem->wait_lock);
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if (waiter.task)
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--
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2.16.4
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