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authorThomas Gleixner <tglx@linutronix.de>2016-10-22 11:07:37 +0000
committerThomas Gleixner <tglx@linutronix.de>2016-10-25 16:32:50 +0200
commit6bad6bccf2d717f652d37e63cf261eaa23466009 (patch)
tree9a22c3c4a778297bf544a0cc89da0c76c8784d6b
parent041ad7bc758db259bb960ef795197dd14aab19a6 (diff)
timers: Prevent base clock corruption when forwarding
When a timer is enqueued we try to forward the timer base clock. This mechanism has two issues: 1) Forwarding a remote base unlocked The forwarding function is called from get_target_base() with the current timer base lock held. But if the new target base is a different base than the current base (can happen with NOHZ, sigh!) then the forwarding is done on an unlocked base. This can lead to corruption of base->clk. Solution is simple: Invoke the forwarding after the target base is locked. 2) Possible corruption due to jiffies advancing This is similar to the issue in get_net_timer_interrupt() which was fixed in the previous patch. jiffies can advance between check and assignement and therefore advancing base->clk beyond the next expiry value. So we need to read jiffies into a local variable once and do the checks and assignment with the local copy. Fixes: a683f390b93f("timers: Forward the wheel clock whenever possible") Reported-by: Ashton Holmes <scoopta@gmail.com> Reported-by: Michael Thayer <michael.thayer@oracle.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Michal Necasek <michal.necasek@oracle.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: knut.osmundsen@oracle.com Cc: stable@vger.kernel.org Cc: stern@rowland.harvard.edu Cc: rt@linutronix.de Link: http://lkml.kernel.org/r/20161022110552.253640125@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--kernel/time/timer.c23
1 files changed, 10 insertions, 13 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 7c446fb5163a..c611c47de884 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -878,7 +878,7 @@ static inline struct timer_base *get_timer_base(u32 tflags)
#ifdef CONFIG_NO_HZ_COMMON
static inline struct timer_base *
-__get_target_base(struct timer_base *base, unsigned tflags)
+get_target_base(struct timer_base *base, unsigned tflags)
{
#ifdef CONFIG_SMP
if ((tflags & TIMER_PINNED) || !base->migration_enabled)
@@ -891,25 +891,27 @@ __get_target_base(struct timer_base *base, unsigned tflags)
static inline void forward_timer_base(struct timer_base *base)
{
+ unsigned long jnow = READ_ONCE(jiffies);
+
/*
* We only forward the base when it's idle and we have a delta between
* base clock and jiffies.
*/
- if (!base->is_idle || (long) (jiffies - base->clk) < 2)
+ if (!base->is_idle || (long) (jnow - base->clk) < 2)
return;
/*
* If the next expiry value is > jiffies, then we fast forward to
* jiffies otherwise we forward to the next expiry value.
*/
- if (time_after(base->next_expiry, jiffies))
- base->clk = jiffies;
+ if (time_after(base->next_expiry, jnow))
+ base->clk = jnow;
else
base->clk = base->next_expiry;
}
#else
static inline struct timer_base *
-__get_target_base(struct timer_base *base, unsigned tflags)
+get_target_base(struct timer_base *base, unsigned tflags)
{
return get_timer_this_cpu_base(tflags);
}
@@ -917,14 +919,6 @@ __get_target_base(struct timer_base *base, unsigned tflags)
static inline void forward_timer_base(struct timer_base *base) { }
#endif
-static inline struct timer_base *
-get_target_base(struct timer_base *base, unsigned tflags)
-{
- struct timer_base *target = __get_target_base(base, tflags);
-
- forward_timer_base(target);
- return target;
-}
/*
* We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means
@@ -1037,6 +1031,9 @@ __mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
}
}
+ /* Try to forward a stale timer base clock */
+ forward_timer_base(base);
+
timer->expires = expires;
/*
* If 'idx' was calculated above and the base time did not advance