From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugene Shatokhin Subject: Re: i915: NULL pointer dereference in i915_update_dri1_breadcrumb() during shutdown Date: Tue, 10 Dec 2013 18:25:42 +0400 Message-ID: <52A72466.8050606@rosalab.ru> References: <52A6D08B.1040802@rosalab.ru> <20131210122351.GF9804@phenom.ffwll.local> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20131210122351.GF9804@phenom.ffwll.local> Sender: linux-kernel-owner@vger.kernel.org To: Daniel Vetter Cc: intel-gfx@lists.freedesktop.org, LKML List-Id: intel-gfx@lists.freedesktop.org On 12/10/2013 04:23 PM, Daniel Vetter wrote: > On Tue, Dec 10, 2013 at 12:27:55PM +0400, Eugene Shatokhin wrote: >> Hi, >> >> I have recently observed a NULL pointer dereference in i915 driver >> on my Eee PC running ROSA Linux with kernel 3.10.21. >> >> The crash occurs during shutdown but quite rarely, not each time. >> >> The system log is lost but here is what I extracted from the info >> displayed on the screen. >> >> NULL pointer dereference at 0x4 >> EIP is at i915_update_dri1_breadcrumb+0x25/0x70 >> comm: systemd-journal >> >> i915_update_dri1_breadcrumb+0x25: >> mov 0x4(%eax),%ebx // %eax contains 0, the list of register >> values confirms that. >> >> That is the reading of 'master_priv->sarea_priv': >> >> void i915_update_dri1_breadcrumb(struct drm_device *dev) >> { >> drm_i915_private_t *dev_priv = dev->dev_private; >> struct drm_i915_master_private *master_priv; >> >> if (dev->primary->master) { >> master_priv = dev->primary->master->driver_priv; >> if (master_priv->sarea_priv) // <<< crashes here >> master_priv->sarea_priv->last_dispatch = >> READ_BREADCRUMB(dev_priv); >> } >> } > > Indeed, that's fairly hapzardous. But also only needed for legacy ums > support. I'll send out a patch to block this in kms mode quickly. Please > test it. > > Thanks, Daniel Thanks a lot! I am building kernel 3.10.23 now with this patch applied and will let you know if something goes wrong. Regards, Eugene -- Eugene Shatokhin, ROSA Laboratory. www.rosalab.com