Re: kernel BUG at kernel/exit.c:792!

[Linus Torvalds]

On Wed, 3 Dec 2003, Srivatsa Vaddagiri wrote:
>
> 	I hit a kernel BUG while running some stress tests
> on a SMP machine. Details are below:
>
> Kernel	:  2.6.0-test9-bk23  + CPU Hotplug Patch
> Machine	:  Intel 4-Way SMP box
>
> kernel BUG at kernel/exit.c:792!
> EIP is at next_thread+0x16/0x50
> Call Trace:
>  [<c0180328>] get_tid_list+0x58/0x70
>  [<c0180524>] proc_task_readdir+0xc4/0x17c
>  [<c01658dc>] vfs_readdir+0x5c/0x70
>  [<c0165be0>] filldir64+0x0/0x120
>  [<c0165d64>] sys_getdents64+0x64/0xa3
>  [<c0165be0>] filldir64+0x0/0x120
>  [<c0109291>] sysenter_past_esp+0x52/0x71
>
> I suspect this is because when read_lock call in 'get_tid_list'
> returns, the leader_task had exited already. This
> causes the NULL sighand check to fail in the subsequent call
> to 'next_thread' ?

Yup, looks right.

I think the problem is the BUG() itself, not really the caller. So I'd
prefer the fix for this to be to just entirely remove the debug tests
withing that "#ifdef CONFIG_SMP", rather than hide the threads from /proc
when this happens.

Ingo, comments?

			Linus
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