Den 05.01.2019 19.25, skrev Noralf Trønnes: > > > Den 24.12.2018 16.03, skrev Peter Wu: >> On Mon, Dec 24, 2018 at 03:52:55PM +0100, Noralf Trønnes wrote: >>> >>> >>> Den 24.12.2018 00.10, skrev Peter Wu: >>>> On Sun, Dec 23, 2018 at 02:55:52PM +0100, Noralf Trønnes wrote: >>>>> >>>>> >>>>> Den 23.12.2018 01.55, skrev Peter Wu: >>>>>> After drm_fb_helper_fbdev_setup calls drm_fb_helper_init, >>>>>> "dev->fb_helper" will be initialized (and thus drm_fb_helper_fini >>>>>> will >>>>>> have some effect). After that, drm_fb_helper_initial_config is called >>>>>> which may call the "fb_probe" driver callback. >>>>>> >>>>>> This driver callback may call drm_fb_helper_defio_init (as is done by >>>>>> drm_fb_helper_generic_probe) or set a framebuffer (as is done by >>>>>> bochs) >>>>>> as documented. These are normally cleaned up on exit by >>>>>> drm_fb_helper_fbdev_teardown which also calls drm_fb_helper_fini. >>>>>> >>>>>> If an error occurs after "fb_probe", but before setup is complete, >>>>>> then >>>>>> calling just drm_fb_helper_fini will leak resources. This was >>>>>> triggered >>>>>> by df2052cc922 ("bochs: convert to >>>>>> drm_fb_helper_fbdev_setup/teardown"): >>>>>> >>>>>> [ 50.008030] bochsdrmfb: enable CONFIG_FB_LITTLE_ENDIAN >>>>>> to support this framebuffer >>>>>> [ 50.009436] bochs-drm 0000:00:02.0: >>>>>> [drm:drm_fb_helper_fbdev_setup] *ERROR* fbdev: Failed to set >>>>>> configuration (ret=-38) >>>>>> [ 50.011456] [drm] Initialized bochs-drm 1.0.0 20130925 >>>>>> for 0000:00:02.0 on minor 2 >>>>>> [ 50.013604] WARNING: CPU: 1 PID: 1 at >>>>>> drivers/gpu/drm/drm_mode_config.c:477 >>>>>> drm_mode_config_cleanup+0x280/0x2a0 >>>>>> [ 50.016175] CPU: 1 PID: 1 Comm: swapper/0 Tainted: >>>>>> G T 4.20.0-rc7 #1 >>>>>> [ 50.017732] EIP: drm_mode_config_cleanup+0x280/0x2a0 >>>>>> ... >>>>>> [ 50.023155] Call Trace: >>>>>> [ 50.023155] ? bochs_kms_fini+0x1e/0x30 >>>>>> [ 50.023155] ? bochs_unload+0x18/0x40 >>>>>> >>>>>> This can be reproduced with QEMU and CONFIG_FB_LITTLE_ENDIAN=n. >>>>>> >>>>>> Link: https://lkml.kernel.org/r/20181221083226.GI23332@shao2-debian >>>>>> Link: https://lkml.kernel.org/r/20181223004315.GA11455@al >>>>>> Fixes: 8741216396b2 ("drm/fb-helper: Add >>>>>> drm_fb_helper_fbdev_setup/teardown()") >>>>>> Reported-by: kernel test robot <rong.a.c...@intel.com> >>>>>> Cc: Noralf Trønnes <nor...@tronnes.org> >>>>>> Signed-off-by: Peter Wu <pe...@lekensteyn.nl> >>>>>> --- >>>>>> drivers/gpu/drm/drm_fb_helper.c | 2 +- >>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c >>>>>> b/drivers/gpu/drm/drm_fb_helper.c >>>>>> index 9d64f874f965..432e0f3b9267 100644 >>>>>> --- a/drivers/gpu/drm/drm_fb_helper.c >>>>>> +++ b/drivers/gpu/drm/drm_fb_helper.c >>>>>> @@ -2860,7 +2860,7 @@ int drm_fb_helper_fbdev_setup(struct >>>>>> drm_device *dev, >>>>>> return 0; >>>>>> err_drm_fb_helper_fini: >>>>>> - drm_fb_helper_fini(fb_helper); >>>>>> + drm_fb_helper_fbdev_teardown(dev); >>>>> >>>>> This change will break the error path for drm_fbdev_generic_setup() >>>>> because drm_fb_helper_generic_probe() cleans up on error but doesn't >>>>> clear drm_fb_helper->fb resulting in a double >>>>> drm_framebuffer_remove(). >>>> >>>> This should probably considered a bug of drm_fb_helper_generic_probe. >>>> Ownership of fb_helper should remain with the caller. The caller can >>>> detect an error and act accordingly. >>>> >>>>> My assumption has been that the drm_fb_helper_funcs->fb_probe callback >>>>> cleans up its resources on error. Clearly this is not the case for >>>>> bochs, so >>>>> my take on this is that bochsfb_create() needs to clean up on error. >>>> >>>> That assumption still holds for bochs. The problem is this sequence: >>>> - drm_fb_helper_fbdev_setup is called. >>>> - fb_probe succeeds (this is crucial). >>>> - register_framebuffer fails. >>>> - error path of setup is triggered. >>>> >>>> As fb_helper is fully setup by drivers, the drm_fb_helper core should >>>> fully deallocate it again on the error path or else a leak occurs. >>>> >>>>> Gerd has a patchset that switches bochs over to the generic fbdev >>>>> emulation, but ofc that doesn't help with 4.20: >>>>> https://patchwork.freedesktop.org/series/54269/ >>>> >>>> And that does not help with other users of the drm_fb_helper who use >>>> functions like drm_fb_helper_defio_init. They will likely run in the >>>> same problem. >>>> >>>> I don't have a way to test tinydrm or other drivers, but if you force >>>> register_framebuffer to fail, you should be able to reproduce the >>>> problem with drm_fb_helper_generic_probe. >>>> >>> >>> Now I understand. I have looked at the drivers that use drm_fb_helper >>> and no one seem to handle the case where register_framebuffer() is >>> failing. >>> >>> Here's what drivers do when drm_fb_helper_initial_config() fails: >>> >>> Doesn't check: >>> amdgpu >>> virtio >>> >>> Calls drm_fb_helper_fini(): >>> armada >>> ast >>> exynos >>> gma500 >>> hisilicon >>> mgag200 >>> msm >>> nouveau >>> omap >>> radeon >>> rockchip >>> tegra >>> udl >>> bochs - Uses drm_fb_helper_fbdev_setup() >>> qxl - Uses drm_fb_helper_fbdev_setup() >>> vboxvideo - Uses drm_fb_helper_fbdev_setup() >>> >>> Might clean up, not sure: >>> cirrus >>> >>> Looks suspicious: >>> i915 >>> >>> I looked at bochs before it switched to drm_fb_helper_fbdev_setup() and >>> it also just called drm_fb_helper_fini(). >>> >>> It looks like you've uncovered something no one has though about (or >>> not implemented at least). >>> >>> It's not just the framebuffer that's not destroyed, the buffer object >>> is also leaked. drm_mode_config_cleanup() yells about the framebuffer >>> (and frees it), but says nothing about the buffer object. It might be >>> that it can't even be made to detect that since some drivers do special >>> stuff for the fbdev buffer. >>> >>> I'll pick up on this and do some testing after the Christmas holidays. >> >> Thanks, the warning is bad for CI (which uses QEMU), but otherwise it >> should not have any effect on regular users so it can wait. >> > > This patch is good as long as it's applied along side the fix[1] to the > generic emulation: > > Reviewed-by: Noralf Trønnes <nor...@tronnes.org> > > I can apply them both when I get an ack/rb on the other patch. >
Applied to drm-misc-next. Noralf. _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel