Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935175AbcJTOe6 (ORCPT ); Thu, 20 Oct 2016 10:34:58 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:34159 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753224AbcJTOe4 (ORCPT ); Thu, 20 Oct 2016 10:34:56 -0400 Date: Thu, 20 Oct 2016 16:34:51 +0200 From: Daniel Vetter To: Takashi Iwai Cc: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , dri-devel@lists.freedesktop.org, Daniel Vetter , linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/fb-helper: Fix race between deferred_io worker and dirty updater Message-ID: <20161020143451.GV20761@phenom.ffwll.local> Mail-Followup-To: Takashi Iwai , Ville =?iso-8859-1?Q?Syrj=E4l=E4?= , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20161020132055.9646-1-tiwai@suse.de> <20161020132814.GT4329@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 4.6.0-1-amd64 User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3393 Lines: 90 On Thu, Oct 20, 2016 at 03:36:54PM +0200, Takashi Iwai wrote: > On Thu, 20 Oct 2016 15:28:14 +0200, > Ville Syrj?l? wrote: > > > > On Thu, Oct 20, 2016 at 03:20:55PM +0200, Takashi Iwai wrote: > > > Since 4.7 kernel, we've seen the error messages like > > > > > > kernel: [TTM] Buffer eviction failed > > > kernel: qxl 0000:00:02.0: object_init failed for (4026540032, 0x00000001) > > > kernel: [drm:qxl_alloc_bo_reserved [qxl]] *ERROR* failed to allocate VRAM BO > > > > > > on QXL when switching and accessing on VT. The culprit was the generic > > > deferred_io code (qxl driver switched to it since 4.7). There is a > > > race between the dirty clip update and the call of callback. > > > > > > In drm_fb_helper_dirty(), the dirty clip is updated in the spinlock, > > > while it kicks off the update worker outside the spinlock. Meanwhile > > > the update worker clears the dirty clip in the spinlock, too. Thus, > > > when drm_fb_helper_dirty() is called concurrently, schedule_work() is > > > called after the clip is cleared in the first worker call. > > > > Why does that matter? The first worker should have done all the > > necessary work already, no? > > Before the first call, it clears the clip and passes the copied clip > to the callback. Then the second call will be with the cleared and > untouched clip, i.e. with x1=~0. This confuses > qxl_framebuffer_dirty(). > > Of course, we can filter out in the callback side by checking the > clip. It was actually my first version. But basically it's a race > and should be covered better in the caller side. Hm, I thought schedule_work also schedules the work when it's getting processed right now. Which means if you're super unlucky you can still end up with the work hitting an empty rectangle. I think filtering empty rects in the worker is what we need to do instead. Or is coffee not working right now? -Daniel > > > thanks, > > Takashi > > > > > > > > > The fix is simply moving schedule_work() inside the spinlock. > > > > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98322 > > > Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1003298 > > > Fixes: eaa434defaca ('drm/fb-helper: Add fb_deferred_io support') > > > Signed-off-by: Takashi Iwai > > > --- > > > drivers/gpu/drm/drm_fb_helper.c | 3 +-- > > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > > > index 03414bde1f15..bae392dea2cc 100644 > > > --- a/drivers/gpu/drm/drm_fb_helper.c > > > +++ b/drivers/gpu/drm/drm_fb_helper.c > > > @@ -861,9 +861,8 @@ static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y, > > > clip->y1 = min_t(u32, clip->y1, y); > > > clip->x2 = max_t(u32, clip->x2, x + width); > > > clip->y2 = max_t(u32, clip->y2, y + height); > > > - spin_unlock_irqrestore(&helper->dirty_lock, flags); > > > - > > > schedule_work(&helper->dirty_work); > > > + spin_unlock_irqrestore(&helper->dirty_lock, flags); > > > } > > > > > > /** > > > -- > > > 2.10.1 > > > > > > _______________________________________________ > > > dri-devel mailing list > > > dri-devel@lists.freedesktop.org > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > > Ville Syrj?l? > > Intel OTC > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch