linux-kernel - Re: libata-core.c: unsafe cancel_delayed

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Message-ID: <20070501234822.GA277@tv-sign.ru>
Date:	Wed, 2 May 2007 03:48:22 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: libata-core.c: unsafe cancel_delayed_work() usage?

On 05/01, Jeff Garzik wrote:
>
> Oleg Nesterov wrote:
> >
> >Alan, the usage of cancel_delayed_work() in drivers/ata/libata-core.c looks
> >suspicious to me, both ->hotplug_task and ->port_task can re-arm 
> >themselves,
> >so cancel_delayed_work + flush_workqueue (or cancel_work_sync) is not 
> >enough.
> >
> >Could you confirm/nack my understanding?
> 
> For all rearming workqueues, one must use cancel-rearming-blahblah.

Well, yes and no. cancel_rearming_delayed_work() requires that dwork
re-arms itself unconditionally, otherwise it just hangs (actually, the
patch to fix this shortcoming is ready). However, ata_pio_task() for
example, re-arms only when ATA_BUSY.

So it is very possible that the code is correct, if the caller of
ata_port_flush_task() ensures that ATA_BUSY is not possible. Otherwise
we should change cancel_rearming_delayed_work() and use it.

Oleg.

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