| Message ID | 20210818073824.1560124-9-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm, kernel: update locking for DRM | expand |
On Wed, Aug 18, 2021 at 03:38:23PM +0800, Desmond Cheong Zhi Xi wrote: > The task_work_add function is needed to prevent userspace races with > DRM modesetting rights. > > Some DRM ioctls can change modesetting permissions while other > concurrent users are performing modesetting. To prevent races with > userspace, such functions should flush readers of old permissions > before returning to user mode. As the function that changes > permissions might itself be a reader of the old permissions, we intend > to schedule this flush using task_work_add. > > However, when DRM is compiled as a loadable kernel module without > exporting task_work_add, we get the following compilation error: > > ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined! > > Reported-by: kernel test robot <lkp@intel.com> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Just realized another benefit of pushing the dev->master_rwsem write locks down into ioctls that need them: We wouldn't need this function here exported for use in drm. But also I'm not sure that works any better than the design in your current patch set ... -Daniel > --- > kernel/task_work.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/task_work.c b/kernel/task_work.c > index 1698fbe6f0e1..90000404af2b 100644 > --- a/kernel/task_work.c > +++ b/kernel/task_work.c > @@ -60,6 +60,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work, > > return 0; > } > +EXPORT_SYMBOL(task_work_add); > > /** > * task_work_cancel_match - cancel a pending work added by task_work_add() > -- > 2.25.1 >
On 19/8/21 5:26 pm, Christoph Hellwig wrote: > On Wed, Aug 18, 2021 at 03:38:23PM +0800, Desmond Cheong Zhi Xi wrote: >> +EXPORT_SYMBOL(task_work_add); > > EXPORT_SYMBOL_GPL for this kinds of functionality, please. > Thanks, I wasn't aware of the GPL-only export. I'll update this in a future series if we still need the export.
diff --git a/kernel/task_work.c b/kernel/task_work.c index 1698fbe6f0e1..90000404af2b 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -60,6 +60,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work, return 0; } +EXPORT_SYMBOL(task_work_add); /** * task_work_cancel_match - cancel a pending work added by task_work_add()
The task_work_add function is needed to prevent userspace races with DRM modesetting rights. Some DRM ioctls can change modesetting permissions while other concurrent users are performing modesetting. To prevent races with userspace, such functions should flush readers of old permissions before returning to user mode. As the function that changes permissions might itself be a reader of the old permissions, we intend to schedule this flush using task_work_add. However, when DRM is compiled as a loadable kernel module without exporting task_work_add, we get the following compilation error: ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined! Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- kernel/task_work.c | 1 + 1 file changed, 1 insertion(+)