Messages in this thread | | | Date | Mon, 19 Oct 2009 14:13:27 +0200 | From | Oleg Nesterov <> | Subject | Re: Kernel oops when clearing bgp neighbor info with TCP MD5SUM enabled |
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Hi Anirban,
On 10/18, Anirban Sinha wrote: > > I have a question for you. The queue_work() routine which is called from > schedule_work() does a put_cpu() which in turn does a enable_preempt(). Is > this an attempt to trigger the scheduler?
No. please note that queue_work() does get_cpu() + put_cpu() to protect against cpu_down() in between.
This can trigger the scheduler of course, but everything should be OK.
> One of the side affects of > this enable_preempt() is the crash that we see below. What is happening > is that a timer callback routine, in this case inet_twdr_hangman(), > tries a bunch of cleanup until a threshold is reached. If further cleanups > needs to be done beyond the threshold, it queues a work function. Now when > the timer callback is run in __run_timers(), the routine grabs the value > of preempt_count before and after the callback function call. If the two > counts do not match, it calls BUG() (line 1037 in kernel/timer.c).
Yes, but I can't see how queue_work() can be involved, it doesn't change ->preempt_count. Note again it does put after get.
> Is is > it illegal to schedule a work function from within a timer callback?
Yes sure.
I'd suppose that this unbalance comes from inet_twdr_hangman() pathes.
Could you verify this?
Oleg.
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