From: "tip-bot2 for Eric Dumazet" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Eric Dumazet <edumazet@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
linux-kernel@vger.kernel.org
Subject: [tip: timers/urgent] hrtimer: Annotate lockless access to timer->base
Date: Mon, 14 Oct 2019 13:58:50 -0000 [thread overview]
Message-ID: <157106153080.9978.2971873792879229342.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20191008173204.180879-1-edumazet@google.com>
The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: ff229eee3d897f52bd001c841f2d3cce8853ecdc
Gitweb: https://git.kernel.org/tip/ff229eee3d897f52bd001c841f2d3cce8853ecdc
Author: Eric Dumazet <edumazet@google.com>
AuthorDate: Tue, 08 Oct 2019 10:32:04 -07:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 14 Oct 2019 15:51:49 +02:00
hrtimer: Annotate lockless access to timer->base
Followup to commit dd2261ed45aa ("hrtimer: Protect lockless access
to timer->base")
lock_hrtimer_base() fetches timer->base without lock exclusion.
Compiler is allowed to read timer->base twice (even if considered dumb)
which could end up trying to lock migration_base and return
&migration_base.
base = timer->base;
if (likely(base != &migration_base)) {
/* compiler reads timer->base again, and now (base == &migration_base)
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
return base; /* == &migration_base ! */
Similarly the write sides must use WRITE_ONCE() to avoid store tearing.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191008173204.180879-1-edumazet@google.com
---
kernel/time/hrtimer.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0d4dc24..6560553 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -164,7 +164,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
struct hrtimer_clock_base *base;
for (;;) {
- base = timer->base;
+ base = READ_ONCE(timer->base);
if (likely(base != &migration_base)) {
raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
if (likely(base == timer->base))
@@ -244,7 +244,7 @@ again:
return base;
/* See the comment in lock_hrtimer_base() */
- timer->base = &migration_base;
+ WRITE_ONCE(timer->base, &migration_base);
raw_spin_unlock(&base->cpu_base->lock);
raw_spin_lock(&new_base->cpu_base->lock);
@@ -253,10 +253,10 @@ again:
raw_spin_unlock(&new_base->cpu_base->lock);
raw_spin_lock(&base->cpu_base->lock);
new_cpu_base = this_cpu_base;
- timer->base = base;
+ WRITE_ONCE(timer->base, base);
goto again;
}
- timer->base = new_base;
+ WRITE_ONCE(timer->base, new_base);
} else {
if (new_cpu_base != this_cpu_base &&
hrtimer_check_target(timer, new_base)) {
prev parent reply other threads:[~2019-10-14 13:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 17:32 [PATCH] hrtimer: annotate lockless access to timer->base Eric Dumazet
2019-10-14 4:10 ` Eric Dumazet
2019-10-14 13:58 ` tip-bot2 for Eric Dumazet [this message]
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