linux-kernel - Re: [PATCH] elv_unregister: fix possible crash on module unload

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Date:	Tue, 22 Aug 2006 15:05:56 +0200
From:	Jens Axboe <axboe@...e.de>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Greg KH <greg@...ah.com>
Subject: Re: [PATCH] elv_unregister: fix possible crash on module unload

On Tue, Aug 22 2006, Oleg Nesterov wrote:
> An exiting task or process which didn't do I/O yet have no io context,
> elv_unregister() should check it is not NULL.
> 
> Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
> 
> --- 2.6.18-rc4/block/elevator.c~8_crash	2006-07-16 01:53:08.000000000 +0400
> +++ 2.6.18-rc4/block/elevator.c	2006-08-22 21:13:06.000000000 +0400
> @@ -765,7 +765,8 @@ void elv_unregister(struct elevator_type
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
>  			task_lock(p);
> -			e->ops.trim(p->io_context);
> +			if (p->io_context)
> +				e->ops.trim(p->io_context);
>  			task_unlock(p);
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);

Good catch, applied. Thanks! I wonder why this hasn't been seen on
switching io schedulers, which makes me a little suspicious. Did you see
it trigger?

-- 
Jens Axboe

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