Re: fix __exit_mm() dereference before check.

[Linus Torvalds]

On Fri, 16 Apr 2004, Dave Jones wrote:
>
> From a quick look, it appears passing NULL mm's down to mm_release()
> isn't a good idea.

Hmm.. Where's the dereference? I don't disagree with the patch per se, but 
I don't see any real problem.

The mm->mm_users check is protected by "tsk->clear_child_tid", and that 
will have been cleared already if we ever happen to call __exit_mm() 
twice, so that one is safe.

So this patch might be a cleanup, but not a "fix" per se.

			Linus

> --- linux-2.6.5/kernel/exit.c~	2004-04-16 22:06:00.000000000 +0100
> +++ linux-2.6.5/kernel/exit.c	2004-04-16 22:06:51.000000000 +0100
> @@ -482,9 +482,10 @@
>  {
>  	struct mm_struct *mm = tsk->mm;
>  
> -	mm_release(tsk, mm);
>  	if (!mm)
>  		return;
> +	mm_release(tsk, mm);
> +
>  	/*
>  	 * Serialize with any possible pending coredump.
>  	 * We must hold mmap_sem around checking core_waiters
> 
-
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