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Message-id: <5412CEDF.7030806@samsung.com> Date: Fri, 12 Sep 2014 19:45:51 +0900 From: Inki Dae <inki.dae@...sung.com> To: Andrzej Hajda <a.hajda@...sung.com> Cc: "moderated list:ARM/S5P EXYNOS AR..." <linux-samsung-soc@...r.kernel.org>, Seung-Woo Kim <sw0312.kim@...sung.com>, open list <linux-kernel@...r.kernel.org>, dri-devel@...ts.freedesktop.org, Kyungmin Park <kyungmin.park@...sung.com>, Marek Szyprowski <m.szyprowski@...sung.com> Subject: Re: [PATCH 5/9] drm/exynos/crtc: fix framebuffer reference sequence On 2014년 09월 12일 18:27, Andrzej Hajda wrote: > On 09/12/2014 10:57 AM, Daniel Vetter wrote: >> On Fri, Sep 12, 2014 at 05:34:50PM +0900, Inki Dae wrote: >>> Hi Andrzej, >>> >>> On 2014년 09월 09일 22:16, Andrzej Hajda wrote: >>>> Adding reference to framebuffer should be accompanied with removing >>>> reference to old framebuffer assigned to the plane. >>>> This patch removes following warning: >>>> >>>> [ 95.038017] WARNING: CPU: 1 PID: 3067 at drivers/gpu/drm/drm_crtc.c:5115 drm_mode_config_cleanup+0x258/0x268() >>>> [ 95.048086] Modules linked in: >>>> [ 95.051430] CPU: 1 PID: 3067 Comm: bash Tainted: G W 3.16.0-11355-g7a6eca5-dirty #3015 >>>> [ 95.060058] [<c0013e90>] (unwind_backtrace) from [<c0011128>] (show_stack+0x10/0x14) >>>> [ 95.067766] [<c0011128>] (show_stack) from [<c04a5dc4>] (dump_stack+0x70/0xbc) >>>> [ 95.074953] [<c04a5dc4>] (dump_stack) from [<c0021784>] (warn_slowpath_common+0x64/0x88) >>>> [ 95.083005] [<c0021784>] (warn_slowpath_common) from [<c00217c4>] (warn_slowpath_null+0x1c/0x24) >>>> [ 95.091780] [<c00217c4>] (warn_slowpath_null) from [<c0275fa0>] (drm_mode_config_cleanup+0x258/0x268) >>>> [ 95.100983] [<c0275fa0>] (drm_mode_config_cleanup) from [<c0281724>] (exynos_drm_unload+0x38/0x50) >>>> [ 95.109915] [<c0281724>] (exynos_drm_unload) from [<c026e248>] (drm_dev_unregister+0x24/0x98) >>>> [ 95.118414] [<c026e248>] (drm_dev_unregister) from [<c026ecb0>] (drm_put_dev+0x28/0x64) >>>> [ 95.126412] [<c026ecb0>] (drm_put_dev) from [<c02947c4>] (take_down_master+0x24/0x44) >>>> [ 95.134218] [<c02947c4>] (take_down_master) from [<c0294870>] (component_del+0x8c/0xc8) >>>> [ 95.142201] [<c0294870>] (component_del) from [<c0286c10>] (exynos_dsi_remove+0x18/0x2c) >>>> [ 95.150294] [<c0286c10>] (exynos_dsi_remove) from [<c0299e04>] (platform_drv_remove+0x18/0x1c) >>>> [ 95.158872] [<c0299e04>] (platform_drv_remove) from [<c02987a4>] (__device_release_driver+0x70/0xc4) >>>> [ 95.167981] [<c02987a4>] (__device_release_driver) from [<c0298818>] (device_release_driver+0x20/0x2c) >>>> [ 95.177268] [<c0298818>] (device_release_driver) from [<c02979d0>] (unbind_store+0x5c/0x94) >>>> [ 95.185597] [<c02979d0>] (unbind_store) from [<c0297278>] (drv_attr_store+0x20/0x2c) >>>> [ 95.193323] [<c0297278>] (drv_attr_store) from [<c012aa90>] (sysfs_kf_write+0x4c/0x50) >>>> [ 95.201224] [<c012aa90>] (sysfs_kf_write) from [<c0129e94>] (kernfs_fop_write+0xc4/0x184) >>>> [ 95.209393] [<c0129e94>] (kernfs_fop_write) from [<c00d03ec>] (vfs_write+0xa0/0x1a8) >>>> [ 95.217111] [<c00d03ec>] (vfs_write) from [<c00d07f8>] (SyS_write+0x40/0x8c) >>>> [ 95.224146] [<c00d07f8>] (SyS_write) from [<c000e660>] (ret_fast_syscall+0x0/0x48) >>>> >>>> Signed-off-by: Andrzej Hajda <a.hajda@...sung.com> >>>> --- >>>> drivers/gpu/drm/exynos/exynos_drm_crtc.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c >>>> index b68e58f..bde19f4 100644 >>>> --- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c >>>> +++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c >>>> @@ -145,10 +145,16 @@ exynos_drm_crtc_mode_set(struct drm_crtc *crtc, struct drm_display_mode *mode, >>>> if (ret) >>>> return ret; >>>> >>>> + /* we need to unreference current fb after replacing it with new one */ >>>> + old_fb = plane->fb; >>>> + >>>> plane->crtc = crtc; >>>> plane->fb = crtc->primary->fb; >>>> drm_framebuffer_reference(plane->fb); >>>> >>>> + if (old_fb) >>>> + drm_framebuffer_unreference(old_fb); >>> This time would be a good chance that we can consider drm flip queue to >>> make sure that whole memory region to old_fb is scanned out completely >>> before dropping a reference of old_fb. the reference of old_fb should be >>> dropped at irq handler of each crtc devices, fimd and mixer. >> Generally it's not a good idea to drop fb references from irq context, >> since if you actually drop the last reference it'll blow up: fb cleanup >> needs a bunch of mutexes. > > I agree with that. > >> >> Also the drm core really should be taking care of this for you, you only >> need to grab references yourself for async flips if you want the buffer to >> survive a bit. crtc_mode_set has not need for this. I expect that the >> refcounting bug is somewhere else, at least from my experience chasing >> such issues in i915 ;-) > > Hmm, maybe I miss something but I do not see the core grabbing fb reference > on plane->fb update. On the other side drm_framebuffer_remove calls > drm_plane_force_disable which drops plane->fb reference. > I am not yet familiar with this code so maybe there is better solution. > > If not I guess it would be better to move this code to > exynos_plane_mode_set. > At least it is done this way in omap and msm, in fact it seems better place I cannot see it in msm. In case of msm, drm flip queue is used in mdp4/5_crtc_mode_set function. See update_fb function there. > for such things. What do you think? > > Regards > Andrzej > >> -Daniel > > -- > To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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