Messages in this thread Patch in this message | | | Date | Tue, 19 Mar 2013 13:29:55 +0100 | From | David Engraf <> | Subject | [PATCH] ktime_add_ns() may overflow on 32bit architectures |
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Hello,
I've triggered an overflow when using ktime_add_ns() on a 32bit architecture not supporting CONFIG_KTIME_SCALAR.
When passing a very high value for u64 nsec, e.g. 7881299347898368000 the do_div() function converts this value to seconds (7881299347) which is still to high to pass to the ktime_set() function as long. The result in my case is a negative value.
The problem on my system occurs in the tick-sched.c, tick_nohz_stop_sched_tick() when time_delta is set to timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is valid, thus ktime_add_ns() is called with a too large value resulting in a negative expire value. This leads to an endless loop in the ticker code:
time_delta: 7881299347898368000 expires = ktime_add_ns(last_update, time_delta) expires: negative value
This error doesn't occurs on 64bit or architectures supporting CONFIG_KTIME_SCALAR (e.g. ARM, x86-32).
Best regards - David
Signed-off-by: David Engraf <david.engraf@sysgo.com>
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index cc47812..320a7aa 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -275,6 +275,10 @@ ktime_t ktime_add_ns(const ktime_t kt, u64 nsec) } else { unsigned long rem = do_div(nsec, NSEC_PER_SEC); + /* Make sure nsec fits into long */ + if (unlikely(nsec > KTIME_SEC_MAX)) + return (ktime_t){ .tv64 = KTIME_MAX }; + tmp = ktime_set((long)nsec, rem); } | |