linux-kernel - Re: Locking question for DRM

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Message-ID: <20100423113717.1188415d@lxorguk.ukuu.org.uk>
Date:	Fri, 23 Apr 2010 11:37:17 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Dave Airlie <airlied@...il.com>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: Locking question for DRM

> > and I can't see what makes this safe if the drm_release for the master
> > and a client occur at the same time ?
> 
> lock_kernel in drm_release. We probably need to clean that up.

I don't think that works. drm_open_helper doesn't appear to be under the
BKL merely the struct mutex.

> > The setmaster/dropmaster ioctl seems similar - the various conditional
> > checks are not protected from parallel changes occuring during their
> > execution.
> >
> > Is this a bug or is something clever afoot ?
> 
> These ioctls are also under the BKL.

But setmaster can sleep so the BKL is dropped on contention of the
struct_mutex, ditto dropmaster



Alan
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