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authorThomas Gleixner <tglx@linutronix.de>2010-05-25 20:43:30 +0200
committerThomas Gleixner <tglx@linutronix.de>2010-05-25 21:07:48 +0200
commit8e63d7795e30b4091e303cc8c060509bd8eea742 (patch)
treed5433cf6b0a57b72b0220ff8e1d89ceca6fbd49c /kernel
parentf16a5e347835c6a0ba958535cf6e6c89d50463b8 (diff)
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timers: Fix slack calculation really
commit f00e047ef (timers: Fix slack calculation for expired timers) fixed the issue of slack on expired timers only partially. Linus noticed that jiffies is volatile so it is reloaded twice, which generates bad code. But its worse. This can defeat the time_after() check if jiffies are incremented between time_after() and the slack calculation. Fix it by reading jiffies into a local variable, which prevents the compiler from loading it twice. While at it make the > -1 check into >= 0 which is easier to read. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/timer.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index be394af5bc2..d8decb8d46b 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -747,16 +747,19 @@ EXPORT_SYMBOL(mod_timer_pending);
static inline
unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
{
- unsigned long expires_limit, mask;
+ unsigned long expires_limit, mask, now;
int bit;
expires_limit = expires;
- if (timer->slack > -1)
+ if (timer->slack >= 0) {
expires_limit = expires + timer->slack;
- else if (time_after(expires, jiffies)) /* auto slack: use 0.4% */
- expires_limit = expires + (expires - jiffies)/256;
-
+ } else {
+ now = jiffies;
+ /* No slack, if already expired else auto slack 0.4% */
+ if (time_after(expires, now))
+ expires_limit = expires + (expires - now)/256;
+ }
mask = expires ^ expires_limit;
if (mask == 0)
return expires;