From: Julien Grall <julien.grall@arm.com>
To: linux-rt-users@vger.kernel.org
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, maz@kernel.org,
bigeasy@linutronix.de, rostedt@goodmis.org,
Julien Grall <julien.grall@arm.com>
Subject: [RT PATCH 3/3] hrtimer: Prevent using uninitialized spin_lock in hrtimer_grab_expiry_lock()
Date: Wed, 21 Aug 2019 10:24:09 +0100 [thread overview]
Message-ID: <20190821092409.13225-4-julien.grall@arm.com> (raw)
In-Reply-To: <20190821092409.13225-1-julien.grall@arm.com>
migration_base is used as a placeholder when an hrtimer is switching
between base (see switch_hrtimer_timer_base). It is possible
theoritically possible to have timer->base equal to migration_base.
Even if it is a placeholder, it would pass all the current check in
hrtimer_grab_expiry_lock() leading to use softirq_expiry_lock
uninitialized.
This is can be prevented by checking whether the base is equal to
the placeholder (i.e. migration_base).
Furthermore, all the path leading to hrtimer_grab_expiry_lock() assumes
timer->base and timer->base->cpu_base are always non-NULL. So it is safe
to remove the NULL checks here.
Signed-off-by: Julien Grall <julien.grall@arm.com>
---
I don't have a reproducer so far, but I can't see why it would not be
possible to happen.
---
kernel/time/hrtimer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 119414a2f59c..5eb45a868de9 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -934,7 +934,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
{
struct hrtimer_clock_base *base = READ_ONCE(timer->base);
- if (timer->is_soft && base && base->cpu_base) {
+ if (timer->is_soft && base != &migration_base) {
spin_lock(&base->cpu_base->softirq_expiry_lock);
spin_unlock(&base->cpu_base->softirq_expiry_lock);
}
--
2.11.0
next prev parent reply other threads:[~2019-08-21 9:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 9:24 [RT PATCH 0/3] hrtimer: RT fixes for hrtimer_grab_expiry_lock() Julien Grall
2019-08-21 9:24 ` [RT PATCH 1/3] hrtimer: Use READ_ONCE to access timer->base in hrimer_grab_expiry_lock() Julien Grall
2019-08-21 13:44 ` Sebastian Andrzej Siewior
2019-08-21 13:50 ` Thomas Gleixner
2019-08-21 13:59 ` Sebastian Andrzej Siewior
2019-09-26 21:47 ` Eric Dumazet
2019-08-23 2:12 ` [tip: timers/core] hrtimer: Protect lockless access to timer->base tip-bot2 for Julien Grall
2019-08-21 9:24 ` [RT PATCH 2/3] hrtimer: Don't grab the expiry lock for non-soft hrtimer Julien Grall
2019-08-21 13:49 ` Sebastian Andrzej Siewior
2019-08-21 9:24 ` Julien Grall [this message]
2019-08-21 14:02 ` [RT PATCH 3/3] hrtimer: Prevent using uninitialized spin_lock in hrtimer_grab_expiry_lock() Thomas Gleixner
2019-08-22 10:59 ` Julien Grall
2019-08-23 2:12 ` [tip: timers/core] hrtimer: Don't take expiry_lock when timer is currently migrated tip-bot2 for Julien Grall
2019-09-04 14:15 ` [PATCH] hrtimer: Add a missing bracket and hide `migration_base' on !SMP Sebastian Andrzej Siewior
2019-09-04 14:39 ` Thomas Gleixner
2019-09-04 14:55 ` [PATCH v2] " Sebastian Andrzej Siewior
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