Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-17 Thread Desmond Cheong Zhi Xi 

On 16/8/21 9:59 pm, Daniel Vetter wrote:

On Mon, Aug 16, 2021 at 12:31 PM Desmond Cheong Zhi Xi
 wrote:


On 16/8/21 5:04 pm, Daniel Vetter wrote:

On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi
 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-races-with-modesetting-rights/20210815-234145
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/cf6d8354b7d7953cd866fad004cbb189adfa074f
   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 

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-josh...@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?



Yup, I had to move the spinlock from struct drm_file to struct 
drm_device, but I think that should work.



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



Agreed, there's a lot of overlap between the master_mutex and rwsem so 
this a good opportunity to refactor things.


I'm cleaning up a v3 series now. There's some movement, but most of it 
are fixes to potential bugs that I saw while refactoring. We can see if 
the new version is a better design.







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

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-16 Thread Daniel Vetter 
On Mon, Aug 16, 2021 at 12:31 PM Desmond Cheong Zhi Xi
 wrote:
>
> On 16/8/21 5:04 pm, Daniel Vetter wrote:
> > On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi
> >  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-races-with-modesetting-rights/20210815-234145
> >>> 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/cf6d8354b7d7953cd866fad004cbb189adfa074f
> >>>   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 
> >>>
> >>> 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-josh...@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-...@lists.01.org
> >>>
> >>
> >
> >
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-16 Thread Desmond Cheong Zhi Xi 

On 16/8/21 5:04 pm, Daniel Vetter wrote:

On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi
 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-races-with-modesetting-rights/20210815-234145
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/cf6d8354b7d7953cd866fad004cbb189adfa074f
  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 

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-josh...@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.


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.


For other ioctls, I'll take a closer look on a case-by-case basis.




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

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-16 Thread Daniel Vetter 
On Mon, Aug 16, 2021 at 10:53 AM Desmond Cheong Zhi Xi
 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-races-with-modesetting-rights/20210815-234145
> > 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/cf6d8354b7d7953cd866fad004cbb189adfa074f
> >  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 
> >
> > 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-josh...@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-...@lists.01.org
> >
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-16 Thread Desmond Cheong Zhi Xi 

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-races-with-modesetting-rights/20210815-234145
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/cf6d8354b7d7953cd866fad004cbb189adfa074f
 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 

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-josh...@samsung.com/ [1]



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

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-16 Thread Desmond Cheong Zhi Xi 

On 16/8/21 2:47 am, kernel test robot wrote:

Hi Desmond,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on next-20210813]
[also build test WARNING 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-races-with-modesetting-rights/20210815-234145
base:4b358aabb93a2c654cd1dcab1a25a589f6e2b153
config: arc-randconfig-r031-20210815 (attached as .config)
compiler: arceb-elf-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
 wget 
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O 
~/bin/make.cross
 chmod +x ~/bin/make.cross
 # 
https://github.com/0day-ci/linux/commit/cf6d8354b7d7953cd866fad004cbb189adfa074f
 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
 COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross 
ARCH=arc

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot 

All warnings (new ones prefixed by >>):


drivers/gpu/drm/drm_auth.c:483:6: warning: no previous prototype for 
'master_flush' [-Wmissing-prototypes]

  483 | void master_flush(struct callback_head *cb)
  |  ^~~~



My bad, this should have been declared with static. I'll add it in, thanks.



vim +/master_flush +483 drivers/gpu/drm/drm_auth.c

479 
480 /* After flushing, all readers that might have seen old master/lease
481  * permissions are guaranteed to have completed.
482  */
  > 483  void master_flush(struct callback_head *cb)
484 {
485 struct drm_device *dev = container_of(cb, struct drm_device,
486   master_flush_work);
487 
488 down_write(>master_rwsem);
489 up_write(>master_rwsem);
490 }
491 

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

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-15 Thread kernel test robot 
Hi Desmond,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on next-20210813]
[also build test WARNING 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-races-with-modesetting-rights/20210815-234145
base:4b358aabb93a2c654cd1dcab1a25a589f6e2b153
config: arc-randconfig-r031-20210815 (attached as .config)
compiler: arceb-elf-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
wget 
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O 
~/bin/make.cross
chmod +x ~/bin/make.cross
# 
https://github.com/0day-ci/linux/commit/cf6d8354b7d7953cd866fad004cbb189adfa074f
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
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross 
ARCH=arc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot 

All warnings (new ones prefixed by >>):

>> drivers/gpu/drm/drm_auth.c:483:6: warning: no previous prototype for 
>> 'master_flush' [-Wmissing-prototypes]
 483 | void master_flush(struct callback_head *cb)
 |  ^~~~


vim +/master_flush +483 drivers/gpu/drm/drm_auth.c

   479  
   480  /* After flushing, all readers that might have seen old master/lease
   481   * permissions are guaranteed to have completed.
   482   */
 > 483  void master_flush(struct callback_head *cb)
   484  {
   485  struct drm_device *dev = container_of(cb, struct drm_device,
   486master_flush_work);
   487  
   488  down_write(>master_rwsem);
   489  up_write(>master_rwsem);
   490  }
   491  

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


.config.gz
Description: application/gzip

Re: [PATCH v2] drm: avoid races with modesetting rights

2021-08-15 Thread kernel test robot 
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-races-with-modesetting-rights/20210815-234145
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/cf6d8354b7d7953cd866fad004cbb189adfa074f
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 

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined!

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


.config.gz
Description: application/gzip