Re: [PATCH] do_brk() needs mmap_sem write-locked

[Linus Torvalds]

Looks good, except for a small nit:

On Tue, 11 Jan 2005, Marcelo Tosatti wrote:
> diff -Nur linux-2.6-curr.orig/mm/mmap.c linux-2.6-curr/mm/mmap.c
> --- linux-2.6-curr.orig/mm/mmap.c	2005-01-11 22:48:49.000000000 -0200
> +++ linux-2.6-curr/mm/mmap.c	2005-01-11 23:43:10.704800272 -0200
> @@ -1891,6 +1891,12 @@
>  	}
>  
>  	/*
> +	 * mm->mmap_sem is required to protect against another thread
> +	 * changing the mappings in case we sleep.
> +	 */
> +	WARN_ON(down_read_trylock(&mm->mmap_sem));
> +
> +	/*
>  	 * Clear old maps.  this also does some error checking for us
>  	 */
>   munmap_back:
> 

if that warning ever triggers, mmap_sem will now be locked, and that will 
cause problems. So I suspect it's better to do

	if (down_read_trylock(&mm->mmap_sem)) {
		WARN_ON(1);
		up_read(&mm->mmap_sem);
	}

and move that into a helper function of its own (something like
"verify_mmap_write_lock_held()").

		Linus
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