38 lines
1.6 KiB
Diff
38 lines
1.6 KiB
Diff
From 38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd Mon Sep 17 00:00:00 2001
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From: "Darren Hart (VMware)" <dvhart@infradead.org>
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Date: Fri, 14 Apr 2017 15:31:38 -0700
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Subject: [PATCH 3/4] futex: Clarify mark_wake_futex memory barrier usage
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.11/older/patches-4.11.5-rt1.tar.xz
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Clarify the scenario described in mark_wake_futex requiring the
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smp_store_release(). Update the comment to explicitly refer to the
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plist_del now under __unqueue_futex() (previously plist_del was in the
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same function as the comment).
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Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Link: http://lkml.kernel.org/r/20170414223138.GA4222@fury
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/futex.c | 9 +++++----
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1 file changed, 5 insertions(+), 4 deletions(-)
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -1380,10 +1380,11 @@ static void mark_wake_futex(struct wake_
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wake_q_add(wake_q, p);
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__unqueue_futex(q);
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/*
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- * The waiting task can free the futex_q as soon as
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- * q->lock_ptr = NULL is written, without taking any locks. A
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- * memory barrier is required here to prevent the following
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- * store to lock_ptr from getting ahead of the plist_del.
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+ * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
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+ * is written, without taking any locks. This is possible in the event
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+ * of a spurious wakeup, for example. A memory barrier is required here
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+ * to prevent the following store to lock_ptr from getting ahead of the
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+ * plist_del in __unqueue_futex().
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*/
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smp_store_release(&q->lock_ptr, NULL);
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}
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