Commit-ID: f2d28a2ebcb525a6ec7e2152106ddb385ef52b73
Gitweb: http://git.kernel.org/tip/f2d28a2ebcb525a6ec7e2152106ddb385ef52b73
Author: Guillaume Knispel <gknispel@xxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 17 Mar 2009 16:18:42 +0100
Commit: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 17 Mar 2009 16:25:28 +0100
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@xxxxxxxxxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
LKML-Reference: <20090317161842.0059096b@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/printk.c | 7 +++++--
1 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/printk.c b/kernel/printk.c
index e3602d0..2be7199 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;
--
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