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

From: Linus Torvalds
Date: Wed Dec 03 2003 - 13:21:28 EST

On Wed, 3 Dec 2003, Manfred Spraul wrote:
> But I don't understand the oops:
> __exit_sighand clears current->sighand, and then in the next line
> __unhash_process removes the thread from the task list. But that's under
> write_lock_irq(&tasklist_lock), and get_tid_list runs under
> read_lock(&tasklist_lock). It should be impossible that ->sighand is
> NULL and the task is still listed in the task list.

The /proc filesystem will keep pointers to processes alive, and can reach
them even if the process is otherwise gone.

This is why /proc ends up doing tests like "if (tsk->mm)" etc - because it
literally can see processes after they are dead.

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