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Date: Wed, 23 Apr 2008 10:11:23 -0700
From: Pete Zaitcev <zaitcev@redhat.com>
To: Pekka J Enberg <penberg@cs.helsinki.fi>
Cc: Ingo Molnar <mingo@elte.hu>, Frans Pop <elendil@planet.nl>,
       linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, gregkh@suse.de,
       zaitcev@redhat.com
Subject: Re: [sched-devel/latest] WARNING: at mm/slub.c:2443
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On Wed, 23 Apr 2008 10:38:45 +0300 (EEST), Pekka J Enberg <penberg@cs.helsinki.fi> wrote:

> > The code analysis for usbmon shows nothing. Anyone wants to have
> > a look?

Thanks for taking this little challenge, let's have a look...

> --- a/drivers/usb/mon/mon_text.c
> +++ b/drivers/usb/mon/mon_text.c
> @@ -449,6 +449,7 @@ static struct mon_event_text *mon_text_read_wait(struct mon_reader_text *rp,
>  		if (file->f_flags & O_NONBLOCK) {
>  			set_current_state(TASK_RUNNING);
>  			remove_wait_queue(&rp->wait, &waita);
> +			kmem_cache_free(rp->e_slab, ep);
>  			return ERR_PTR(-EWOULDBLOCK);

The code looks like this:

	while ((ep = mon_text_fetch(rp, mbus)) == NULL) {
		if (file->f_flags & O_NONBLOCK) {
			set_current_state(TASK_RUNNING);
			remove_wait_queue(&rp->wait, &waita);
			return ERR_PTR(-EWOULDBLOCK);

It's impossible to get inside the while() with non-null ep,
so your patch doesn't fix anything (even if kmem_cache_free
can survive a NULL object).

Any other ideas?

-- Pete