linux-kernel - Re: [tip:bkl/drivers] drivers: Remove BKL from misc

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Message-ID: <20091014191223.35ba4004@lxorguk.ukuu.org.uk>
Date:	Wed, 14 Oct 2009 19:12:23 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	gregkh@...e.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:bkl/drivers] drivers: Remove BKL from misc_open

On Wed, 14 Oct 2009 18:16:58 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> on Wed, 14 Oct 2009, Alan Cox wrote:
> > On Wed, 14 Oct 2009 15:47:39 GMT
> > tip-bot for Thomas Gleixner <tglx@...utronix.de> wrote:
> > 
> > > Commit-ID:  40b798efe3460797a4ac928ee2e038774e2758eb
> > > Gitweb:     http://git.kernel.org/tip/40b798efe3460797a4ac928ee2e038774e2758eb
> > > Author:     Thomas Gleixner <tglx@...utronix.de>
> > > AuthorDate: Sat, 10 Oct 2009 15:35:43 +0000
> > > Committer:  Thomas Gleixner <tglx@...utronix.de>
> > > CommitDate: Wed, 14 Oct 2009 17:33:32 +0200
> > > 
> > > drivers: Remove BKL from misc_open
> > > 
> > > misc_open() is already serialized with misc_mtx. Remove the BKL
> > > locking which got there via the BKL pushdown.
> > 
> > NAK.
> > 
> > You can't simply assume the mutex is enough - you have to either push it
> > down or review *every* possible called point below the lock_kernel take.
> > 
> > In this case the open method of the misc devices below sometimes uses the
> > BKL.
> 
> The BKL got pushed down into the open methods of misc dev users and we
> do not need to take it twice in a row, right ?

Then the comment is misleading and you need to document that you've
already pushed the BKL down into each user and checked them.

Alan
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