Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sat, 30 Apr 2005 16:42:34 +0400 | From | Oleg Nesterov <> | Subject | Re: Fw: [Bug 4559] New: cfq scheduler lockup: NMI oops while runningltp - 20050207 on 2.6.12-rc2-mm3 with kdump enabled |
| |
Andrew Morton wrote: > > http://bugme.osdl.org/show_bug.cgi?id=4559 > > Timer bug, I guess.
Yes, the new timer code is racy. Example:
spinlock_t LOCK;
void void timer_func() { spin_lock(&LOCK); }
timer_list TIMER = TIMER_INITIALIZER(timer_func);
------------------------------------------------------------------- CPU_0 CPU_1
add_timer(&TIMER); spin_lock(&LOCK); __run_timers: sets ->running_timer = &TIMER; calls timer_func() waits for &LOCK
__mod_timer(&TIMER); /* Ensure the timer is serialized. */ retries while ->running_timer == &TIMER
Many thanks to Maneesh Soni for his excellent analysis in http://bugme.osdl.org/show_bug.cgi?id=4559.
Note that del_timer_sync has this problem too, but this situation is forbidden by synchronization rules.
At the moment I don't have a proper solution.
One option is to change __mod_timer() so that it would not switch ->base when the timer is already running. But this would be behavioural change: currently __mod_timer() guarantees that the timer would be armed on the local cpu.
I'll try to find a solution, but perhaps it's better to drop this patch for now.
Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| ![\](/images/icornerr.gif) |