Re: [RFC][PATCH][2.5] Possible race in wait_task_zombie and

[Zwane Mwaikambo]

On Sun, 25 May 2003, Manfred Spraul wrote:

> - the reference for the stack itself, acquired by setting usage to 2, 
> dropped by schedule_tail.
> - the reference for wait4, acquired by setting usage to 2, dropped by 
> wait_task_zombie.
> - references for the pid structures, maintained by pid.c
> - temporary references for looking at tsk->{fs,mm,files,tty}, used by 
> /proc, ptrace, tty.

it's the one dropped by wait_task_zombie, the task coming out from 
schedule_tail is fine.

> 
> >kernel BUG at kernel/sched.c:746!
> >  
> >
> Hmm. What is schedule.c:746? There is no BUG in that area in the bk tree.

It's in finish_arch_switch at the put_task_struct()

> Zwane, is it easy to reproduce the crash? I could write a patch that 
> adds 4 refcounters, then we could find out in which area we must look.

I haven't found a direct way of triggering it, so far it's just been 
cropping up ~6 times over a period of 2days with the box normally taking a 
fatal one and dying completely.

	Zwane
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