| Message ID | 20210115133550.1678-1-christian.koenig@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/syncobj: make lockdep complain on WAIT_FOR_SUBMIT | expand |
On Fri, Jan 15, 2021 at 02:35:50PM +0100, Christian König wrote: > DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT can't be used when a reservation > object lock is help or otherwise we can deadlock with page faults. > > Make lockdep complain badly about that. > > Signed-off-by: Christian König <christian.koenig@amd.com> > --- > drivers/gpu/drm/drm_syncobj.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c > index 6e74e6745eca..6228e9cd089a 100644 > --- a/drivers/gpu/drm/drm_syncobj.c > +++ b/drivers/gpu/drm/drm_syncobj.c > @@ -387,6 +387,20 @@ int drm_syncobj_find_fence(struct drm_file *file_private, > if (!syncobj) > return -ENOENT; > > + if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT && > + IS_ENABLED(CONFIG_LOCKDEP)) { > + struct dma_resv robj; > + > + /* Waiting for userspace with a reservation lock help is illegal > + * cause that can deadlock with page faults. Make lockdep > + * complain about it early on. Not sure this is a good enough explanation, since anything that holds up userspace can result in a functional deadlock (i.e. user observes no forward progress, gets angry and decides that our gpu driver stack is garbage). It's by far not pagefault. I'd put something like /* We must not impede forward progress of userspace in any * way, for otherwise the future fence never materializes * and the application grinds to a full halt. Check for * the worst offenders in terms of locking issues. */ Feel free to bikeshed further. > + */ > + dma_resv_init(&robj); > + dma_resv_lock(&robj, NULL); > + dma_resv_unlock(&robj); > + dma_resv_fini(&robj); I think you want to go stronger, since it's not just dma_resv, it's holding anything that might hold up userspace that's illegal here. A lockdep_assert_no_locks_held might be ideal, but a good second-best option would be to grab mmap_lock. Since dma_resv (and a lot of other things, like gup in general) nest within that it would be a substantially stronger asssertion. Specifically this should also go boom when you do it in places like serving (hmm) page faults, which I think we want. Just locking dma_resv_lock wont go boom like that (since taking the dma_resv_lock from a page fault handler is explicitly allowed, it nests within mmap_lock). Conceptually I think it's otherwise all fine and at the right spot. -Daniel > + } > + > *fence = drm_syncobj_fence_get(syncobj); > drm_syncobj_put(syncobj); > > -- > 2.25.1 >
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 6e74e6745eca..6228e9cd089a 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -387,6 +387,20 @@ int drm_syncobj_find_fence(struct drm_file *file_private, if (!syncobj) return -ENOENT; + if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT && + IS_ENABLED(CONFIG_LOCKDEP)) { + struct dma_resv robj; + + /* Waiting for userspace with a reservation lock help is illegal + * cause that can deadlock with page faults. Make lockdep + * complain about it early on. + */ + dma_resv_init(&robj); + dma_resv_lock(&robj, NULL); + dma_resv_unlock(&robj); + dma_resv_fini(&robj); + } + *fence = drm_syncobj_fence_get(syncobj); drm_syncobj_put(syncobj);
DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT can't be used when a reservation object lock is help or otherwise we can deadlock with page faults. Make lockdep complain badly about that. Signed-off-by: Christian König <christian.koenig@amd.com> --- drivers/gpu/drm/drm_syncobj.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)