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authorEric Dumazet <edumazet@google.com>2015-08-17 10:18:48 -0700
committerThomas Gleixner <tglx@linutronix.de>2015-08-18 15:31:16 +0200
commitd0023a1448abdcc892b8bca631e74bb1888efd02 (patch)
tree5fb4ee814e797e980136e7b8623e17648d552121 /kernel/time/timer.c
parenta36304b9e154ccaff67b1d1d0ece6ad6380e3648 (diff)
downloadlinux-sh-d0023a1448abdcc892b8bca631e74bb1888efd02.tar.gz
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/timer.c')
-rw-r--r--kernel/time/timer.c4
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);
}
}