Commit-ID: d0023a1448abdcc892b8bca631e74bb1888efd02
Gitweb: http://git.kernel.org/tip/d0023a1448abdcc892b8bca631e74bb1888efd02
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
AuthorDate: Mon, 17 Aug 2015 10:18:48 -0700
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 18 Aug 2015 15:31:16 +0200
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@xxxxxxxxxx>
Cc: Jon Christopherson <jon@xxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
Cc: david.vrabel@xxxxxxxxxx
Cc: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1439831928.32680.11.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/time/timer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 5e097fa..84190f0 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);
}
}
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