Am 19.03.2013 13:38, schrieb Eric Dumazet:
On Tue, 2013-03-19 at 13:29 +0100, David Engraf wrote:
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.eng...@sysgo.com>
But check already exists for 64bit arches in ktime_set()
Yes, but not for 32bit arches. 64-bit arches doesn't run into this
problem because ktime_add_ns() can directly calculate the result without
calling do_div() and ktime_set().
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