Hi Desmond, Thank you for the patch! Yet something to improve: [auto build test ERROR on next-20210813] [also build test ERROR on v5.14-rc5] [cannot apply to linus/master v5.14-rc5 v5.14-rc4 v5.14-rc3] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Desmond-Cheong-Zhi-Xi/drm-avoid-... base: 4b358aabb93a2c654cd1dcab1a25a589f6e2b153 config: i386-randconfig-a004-20210815 (attached as .config) compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 reproduce (this is a W=1 build): # https://github.com/0day-ci/linux/commit/cf6d8354b7d7953cd866fad004cbb189a... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Desmond-Cheong-Zhi-Xi/drm-avoid-races-with-modesetting-rights/20210815-234145 git checkout cf6d8354b7d7953cd866fad004cbb189adfa074f # save the attached .config to linux build tree make W=1 ARCH=i386 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>, old ones prefixed by <<): >> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined!

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On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi <desmondcheongzx(a)gmail.com&gt; wrote: > On 16/8/21 2:47 am, kernel test robot wrote: >> Hi Desmond, >> >> Thank you for the patch! Yet something to improve: >> >> [auto build test ERROR on next-20210813] >> [also build test ERROR on v5.14-rc5] >> [cannot apply to linus/master v5.14-rc5 v5.14-rc4 v5.14-rc3] >> [If your patch is applied to the wrong git tree, kindly drop us a note. >> And when submitting patch, we suggest to use '--base' as documented in >> https://git-scm.com/docs/git-format-patch] >> >> url: https://github.com/0day-ci/linux/commits/Desmond-Cheong-Zhi-Xi/drm-avoid-... >> base: 4b358aabb93a2c654cd1dcab1a25a589f6e2b153 >> config: i386-randconfig-a004-20210815 (attached as .config) >> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 >> reproduce (this is a W=1 build): >> # https://github.com/0day-ci/linux/commit/cf6d8354b7d7953cd866fad004cbb189a... >> git remote add linux-review https://github.com/0day-ci/linux >> git fetch --no-tags linux-review Desmond-Cheong-Zhi-Xi/drm-avoid-races-with-modesetting-rights/20210815-234145 >> git checkout cf6d8354b7d7953cd866fad004cbb189adfa074f >> # save the attached .config to linux build tree >> make W=1 ARCH=i386 >> >> If you fix the issue, kindly add following tag as appropriate >> Reported-by: kernel test robot <lkp(a)intel.com&gt; >> >> All errors (new ones prefixed by >>, old ones prefixed by <<): >> >>>> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined! >> > > I'm a bit uncertain about this. Looking into the .config used, this > error seems to happen because task_work_add isn't an exported symbol, > but DRM is being compiled as a loadable kernel module (CONFIG_DRM=m). > > One way to deal with this is to export the symbol, but there was a > proposed patch to do this a few months back that wasn't picked up [1], > so I'm not sure what to make of this. > > I'll export the symbol as part of a v3 series, and check in with the > task-work maintainers. > > Link: > https://lore.kernel.org/lkml/20210127150029.13766-3-joshi.k@samsung.com/ [1] Yeah that sounds best. I have two more thoughts on the patch: - drm_master_flush isn't used by any modules outside of drm.ko, so we can unexport it and drop the kerneldoc (the comment is still good). These kind of internal functions have their declaration in drm-internal.h - there's already a few there from drm_auth.c

- We know have 3 locks for master state, that feels a bit like overkill. The spinlock I think we need to keep due to lock inversions, but the master_mutex and master_rwsem look like we should be able to merge them? I.e. anywhere we currently grab the master_mutex we could instead grab the rwsem in either write mode (when we change stuff) or read mode (when we just check, like in master_internal_acquire). Thoughts? -Daniel

> >> --- >> 0-DAY CI Kernel Test Service, Intel Corporation >> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org >> >

On Mon, Aug 16, 2021 at 12:31 PM Desmond Cheong Zhi Xi <desmondcheongzx(a)gmail.com&gt; wrote: > > On 16/8/21 5:04 pm, Daniel Vetter wrote: >> On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi >> <desmondcheongzx(a)gmail.com&gt; wrote: >>> On 16/8/21 2:47 am, kernel test robot wrote: >>>> Hi Desmond, >>>> >>>> Thank you for the patch! Yet something to improve: >>>> >>>> [auto build test ERROR on next-20210813] >>>> [also build test ERROR on v5.14-rc5] >>>> [cannot apply to linus/master v5.14-rc5 v5.14-rc4 v5.14-rc3] >>>> [If your patch is applied to the wrong git tree, kindly drop us a note. >>>> And when submitting patch, we suggest to use '--base' as documented in >>>> https://git-scm.com/docs/git-format-patch] >>>> >>>> url: https://github.com/0day-ci/linux/commits/Desmond-Cheong-Zhi-Xi/drm-avoid-... >>>> base: 4b358aabb93a2c654cd1dcab1a25a589f6e2b153 >>>> config: i386-randconfig-a004-20210815 (attached as .config) >>>> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 >>>> reproduce (this is a W=1 build): >>>> # https://github.com/0day-ci/linux/commit/cf6d8354b7d7953cd866fad004cbb189a... >>>> git remote add linux-review https://github.com/0day-ci/linux >>>> git fetch --no-tags linux-review Desmond-Cheong-Zhi-Xi/drm-avoid-races-with-modesetting-rights/20210815-234145 >>>> git checkout cf6d8354b7d7953cd866fad004cbb189adfa074f >>>> # save the attached .config to linux build tree >>>> make W=1 ARCH=i386 >>>> >>>> If you fix the issue, kindly add following tag as appropriate >>>> Reported-by: kernel test robot <lkp(a)intel.com&gt; >>>> >>>> All errors (new ones prefixed by >>, old ones prefixed by <<): >>>> >>>>>> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined! >>>> >>> >>> I'm a bit uncertain about this. Looking into the .config used, this >>> error seems to happen because task_work_add isn't an exported symbol, >>> but DRM is being compiled as a loadable kernel module (CONFIG_DRM=m). >>> >>> One way to deal with this is to export the symbol, but there was a >>> proposed patch to do this a few months back that wasn't picked up [1], >>> so I'm not sure what to make of this. >>> >>> I'll export the symbol as part of a v3 series, and check in with the >>> task-work maintainers. >>> >>> Link: >>> https://lore.kernel.org/lkml/20210127150029.13766-3-joshi.k@samsung.com/ [1] >> >> Yeah that sounds best. I have two more thoughts on the patch: >> - drm_master_flush isn't used by any modules outside of drm.ko, so we >> can unexport it and drop the kerneldoc (the comment is still good). >> These kind of internal functions have their declaration in >> drm-internal.h - there's already a few there from drm_auth.c >> > > Sounds good, I'll do that and move the declaration from drm_auth.h to > drm_internal.h. > >> - We know have 3 locks for master state, that feels a bit like >> overkill. The spinlock I think we need to keep due to lock inversions, >> but the master_mutex and master_rwsem look like we should be able to >> merge them? I.e. anywhere we currently grab the master_mutex we could >> instead grab the rwsem in either write mode (when we change stuff) or >> read mode (when we just check, like in master_internal_acquire). >> >> Thoughts? >> -Daniel >> > > Using rwsem in the places where we currently hold the mutex seems pretty > doable. > > There are some tricky bits once we add rwsem read locks to the ioctl > handler. Some ioctl functions like drm_authmagic need a write lock. Ah yes, I only looked at the dropmaster/setmaster ioctl, and those don't have the DRM_MASTER bit set. > In this particular case, it might make sense to break master_mutex down > into finer-grained locks, since the function doesn't change master > permissions. It just needs to prevent concurrent writes to the > drm_master.magic_map idr. Yeah for authmagic we could perhaps just reuse the spinlock to protect ->magic_map?

> For other ioctls, I'll take a closer look on a case-by-case basis. If it's too much shuffling then I think totally fine to leave things as-is. Just feels a bit silly to have 3 locks, on of which is an rwlock itself, for this fairly small amount of state. -Daniel

> >>> >>>> --- >>>> 0-DAY CI Kernel Test Service, Intel Corporation >>>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org >>>> >>> >> >> >