Messages in this thread Patch in this message | | | Date | Tue, 17 Mar 2009 16:03:23 GMT | From | Guillaume Knispel <> | Subject | [tip:core/printk] printk: correct the behavior of printk_timed_ratelimit() |
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Commit-ID: f2d28a2ebcb525a6ec7e2152106ddb385ef52b73 Gitweb: http://git.kernel.org/tip/f2d28a2ebcb525a6ec7e2152106ddb385ef52b73 Author: Guillaume Knispel <gknispel@proformatique.com> AuthorDate: Tue, 17 Mar 2009 16:18:42 +0100 Commit: Ingo Molnar <mingo@elte.hu> 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@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>
--- 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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