linux-kernel - Re: [PATCH] drm/sysfs: Do not drop device reference twice

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Message-ID: <20131030211814.GC7686@mithrandir>
Date:	Wed, 30 Oct 2013 22:18:15 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Paulo Zanoni <przanoni@...il.com>
Cc:	David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/sysfs: Do not drop device reference twice

On Wed, Oct 30, 2013 at 02:05:02PM -0200, Paulo Zanoni wrote:
> 2013/10/30 Thierry Reding <thierry.reding@...il.com>:
> > device_unregister() already drops its reference to the struct device, so
> > explicitly calling put_device() before device_unregister() can cause the
> > device to have been freed before it can be unregistered.
> >
> > Signed-off-by: Thierry Reding <treding@...dia.com>
> 
> I started investigating this problem yesterday and reached the same
> conclusion. The connector path can be easily reproduced on i915.ko:
> get a machine that has an eDP panel, physically disconnect the panel,
> boot the machine, "modprobe i915" and watch the segfault.
> 
> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@...el.com>
> Tested-by: Paulo Zanoni <paulo.r.zanoni@...el.com>
> 
> I didn't really bisect, but I believe this is probably a regression
> from "drm/sysfs: sort out minor and connector device object
> lifetimes".

Yes, I think that's the one that broke it.

Thierry

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