Hi,
I came across a strange bug (in a very old kernel) that triggers
the
BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
in __run_hrtimer().
The code runs hrtimer_start() on an already started hrtimer.
Looking at the description of hrtimer_start() it looks
like something that is allowed:
/**
* hrtimer_start - (re)start an hrtimer on the current CPU
...
* Returns:
* 0 on success
* 1 when the timer was active
Is this really supposed to work?
I think it's not immune to this race condition:
CPU0 CPU1
__run_hrtimer()
__remove_hrtimer(...HRTIMER_STATE_CALLBACK)
//clears HRTIMER_STATE_ENQUEUED
...
raw_spin_unlock(&cpu_base->lock);
restart = fn(timer);
hrtimer_start()
__hrtimer_start_range_ns()
//remove_hrtimer() does
nothing because
//
HRTIMER_STATE_ENQUEUED is not set
enqueue_hrtimer()
raw_spin_lock(&cpu_base->lock);
...
BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
// state has HRTIMER_STATE_ENQUEUED set
Should __hrtimer_start_range_ns() do something like
hrtimer_cancel - i.e. explicitly check for ...
HRTIMER_STATE_CALLBACK?
Thanks,
--
Jiri Bohac <[email protected]>
SUSE Labs, SUSE CZ
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