From: Arjan van de Ven <arjan@infradead.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: John Kacur <jkacur@redhat.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@elte.hu>,
Christoph Hellwig <hch@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Andrew Morton <akpm@linux-foundation.org>,
Vincent Sanders <vince@simtec.co.uk>,
linux-scsi@vger.kernel.org
Subject: Re: [PATCH RFC] [PATCH] drivers/scsi/ch.c: Remove BKL in ch_open
Date: Sun, 11 Oct 2009 08:29:17 -0700 [thread overview]
Message-ID: <20091011082917.6ebbd810@infradead.org> (raw)
In-Reply-To: <20091011153709.4438cf9c@lxorguk.ukuu.org.uk>
On Sun, 11 Oct 2009 15:37:09 +0100
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> On Sun, 11 Oct 2009 15:45:16 +0200 (CEST)
> John Kacur <jkacur@redhat.com> wrote:
>
> [linux-scsi cc'd]
>
> > Locking in ch_open is covered by the spin_lock, it serializes the
> > calls to idr_find and scsi_device_get. The BKL appears redundant to
> > me here.
>
> I'm not so sure. In fact there are some quite umm interesting
> questions about this code, and some of them are shared with other
> modules too.
>
> Consider the following sequence
>
> CPU1 CPU2
> register_chrdev
> ok
> open device
> takes lock
but open does not take the BKL, so the BKL is not protecting you at
all against this..
--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org
next prev parent reply other threads:[~2009-10-11 15:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-11 13:45 John Kacur
2009-10-11 14:37 ` Alan Cox
2009-10-11 15:29 ` Arjan van de Ven [this message]
2009-10-11 15:54 ` Alan Cox
2009-10-11 16:03 ` Arjan van de Ven
2009-10-11 16:14 ` Alan Cox
2009-10-11 16:19 ` Arjan van de Ven
2009-10-11 17:09 ` Jonathan Corbet
2009-10-12 13:03 ` Stefan Richter
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