Commit-ID: 8e63d7795e30b4091e303cc8c060509bd8eea742
Gitweb: http://git.kernel.org/tip/8e63d7795e30b4091e303cc8c060509bd8eea742
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 25 May 2010 20:43:30 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 25 May 2010 21:07:48 +0200
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@xxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
kernel/timer.c | 13 ++++++++-----
1 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/timer.c b/kernel/timer.c
index be394af..d8decb8 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;
--
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