diff options
| author | Guillaume Knispel <gknispel@proformatique.com> | 2009-03-17 16:18:42 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-03-17 16:25:28 +0100 |
| commit | f2d28a2ebcb525a6ec7e2152106ddb385ef52b73 (patch) | |
| tree | 207920700ba3c7c7091d547184c883e7bd05a2a8 /kernel/printk.c | |
| parent | 47239561e39bceefecc3cd67f71fcf86a198a8ff (diff) | |
printk: correct the behavior of printk_timed_ratelimit()
Impact: fix jiffies-comparison sign-wrap behavior
The behavior provided by printk_timed_ratelimit() is, in some
situations, probably not what a caller would reasonably expect:
bool printk_timed_ratelimit(unsigned long *caller_jiffies,
unsigned int interval_msecs)
{
if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
*caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
return true;
}
return false;
}
On a 32 bit computer, if printk_timed_ratelimit() is initially called at
time jiffies == Ja, *caller_jiffies is set to
Ja + msecs_to_jiffies(interval_msecs): let's say Ja + 42 for this
example.
If this caller then doesn't call printk_timed_ratelimit() until
jiffies == Ja + (1 << 31) + 42 (which can happen as soon as ~ 25 days
later on a 1000 HZ system), printk_timed_ratelimit() will then always
return false to this caller until jiffies loops completely (1 << 31 more
ticks).
Ths change makes it only return false if jiffies is in the small
time window starting at the previous call when true was returned and
ending interval_msecs later. Note that if jiffies loops completely
between two calls to printk_timed_ratelimit(), it will obviously still
wrongly return false, but this is something with a low probability.
If something completely reliable is needed I guess jiffies_64 must be
used (which this change does not do).
Signed-off-by: Guillaume Knispel <gknispel@proformatique.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20090317161842.0059096b@xilun.lan.proformatique.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/printk.c')
| -rw-r--r-- | kernel/printk.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/printk.c b/kernel/printk.c index e3602d0755b..2be719908d1 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1292,8 +1292,11 @@ EXPORT_SYMBOL(printk_ratelimit); bool printk_timed_ratelimit(unsigned long *caller_jiffies, unsigned int interval_msecs) { - if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) { - *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs); + if (*caller_jiffies == 0 + || !time_in_range(jiffies, *caller_jiffies, + *caller_jiffies + + msecs_to_jiffies(interval_msecs))) { + *caller_jiffies = jiffies; return true; } return false; |