diff options
| author | Eric Dumazet <edumazet@google.com> | 2015-08-17 10:18:48 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2015-08-18 15:31:16 +0200 |
| commit | d0023a1448abdcc892b8bca631e74bb1888efd02 (patch) | |
| tree | 5fb4ee814e797e980136e7b8623e17648d552121 /kernel/time | |
| parent | a36304b9e154ccaff67b1d1d0ece6ad6380e3648 (diff) | |
timer: Write timer->flags atomically
lock_timer_base() cannot prevent the following :
CPU1 ( in __mod_timer()
timer->flags |= TIMER_MIGRATING;
spin_unlock(&base->lock);
base = new_base;
spin_lock(&base->lock);
// The next line clears TIMER_MIGRATING
timer->flags &= ~TIMER_BASEMASK;
CPU2 (in lock_timer_base())
see timer base is cpu0 base
spin_lock_irqsave(&base->lock, *flags);
if (timer->flags == tf)
return base; // oops, wrong base
timer->flags |= base->cpu // too late
We must write timer->flags in one go, otherwise we can fool other cpus.
Fixes: bc7a34b8b9eb ("timer: Reduce timer migration overhead if disabled")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jon Christopherson <jon@jons.org>
Cc: David Miller <davem@davemloft.net>
Cc: xen-devel@lists.xen.org
Cc: david.vrabel@citrix.com
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Link: http://lkml.kernel.org/r/1439831928.32680.11.camel@edumazet-glaptop2.roam.corp.google.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/timer.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 5e097fa9faf7..84190f02b521 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -807,8 +807,8 @@ __mod_timer(struct timer_list *timer, unsigned long expires, spin_unlock(&base->lock); base = new_base; spin_lock(&base->lock); - timer->flags &= ~TIMER_BASEMASK; - timer->flags |= base->cpu; + WRITE_ONCE(timer->flags, + (timer->flags & ~TIMER_BASEMASK) | base->cpu); } } |