linux-kernel - Re: [PATCH 2/2] scsi: don't use execute_in_process

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Message-ID: <1292428486.4688.180.camel@mulgrave.site>
Date:	Wed, 15 Dec 2010 10:54:46 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linux SCSI List <linux-scsi@...r.kernel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] scsi: don't use execute_in_process_context()

On Wed, 2010-12-15 at 16:47 +0100, Tejun Heo wrote:
> One way or the other, the current code is racy.  The module can go
> away while the work is still running.  We'll have to add sync
> interface for ew's, which conceptually is fine but is unnecessary with
> the current code base.  Let's do it when it actually is necessary.

OK, ignoring the bickering over API, this is what I don't get.

The executed function releases the parent reference as its last call.
That will cause the freeing of the embedded work item and a cascade
release of all the parents.  If there's no more references, that will
result in a final put of the module semaphore and rmmod will then
proceed.  What is racy about that?  All the work structures and
references have been freed before the module gets removed.  Nothing
blocks the execution thread in the function, so it exits long before the
code path gets zeroed.

James

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