From: David Engraf Date: Tue, 19 Mar 2013 12:29:55 +0000 (+0100) Subject: hrtimer: Fix ktime_add_ns() overflow on 32bit architectures X-Git-Tag: v3.0.77~17 X-Git-Url: https://git.fsl.cs.sunysb.edu/?a=commitdiff_plain;h=b0f97a448749144ed26634ed47323ce2217a7a4c;p=unionfs-2.6.39.y.git hrtimer: Fix ktime_add_ns() overflow on 32bit architectures commit 51fd36f3fad8447c487137ae26b9d0b3ce77bb25 upstream. One can trigger 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 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 fix caps the value to KTIME_MAX. This error doesn't occurs on 64bit or architectures supporting CONFIG_KTIME_SCALAR (e.g. ARM, x86-32). Signed-off-by: David Engraf [jstultz: Minor tweaks to commit message & header] Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 3c5a22f83cc..d8e856ea560 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -298,6 +298,10 @@ ktime_t ktime_sub_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); }