diff options
authorLeo Li <sunpeng.li@amd.com>2018-10-15 09:46:40 -0400
committerHarry Wentland <harry.wentland@amd.com>2018-10-18 14:23:13 -0400
commit4364bcb2cd21d042bde4776448417ddffbc54045 (patch)
parent9068e02f58740778d8270840657f1e250a2cc60f (diff)
drm: Get ref on CRTC commit object when waiting for flip_done
This fixes a general protection fault, caused by accessing the contents of a flip_done completion object that has already been freed. It occurs due to the preemption of a non-blocking commit worker thread W by another commit thread X. X continues to clear its atomic state at the end, destroying the CRTC commit object that W still needs. Switching back to W and accessing the commit objects then leads to bad results. Worker W becomes preemptable when waiting for flip_done to complete. At this point, a frequently occurring commit thread X can take over. Here's an example where W is a worker thread that flips on both CRTCs, and X does a legacy cursor update on both CRTCs: ... 1. W does flip work 2. W runs commit_hw_done() 3. W waits for flip_done on CRTC 1 4. > flip_done for CRTC 1 completes 5. W finishes waiting for CRTC 1 6. W waits for flip_done on CRTC 2 7. > Preempted by X 8. > flip_done for CRTC 2 completes 9. X atomic_check: hw_done and flip_done are complete on all CRTCs 10. X updates cursor on both CRTCs 11. X destroys atomic state 12. X done 13. > Switch back to W 14. W waits for flip_done on CRTC 2 15. W raises general protection fault The error looks like so: general protection fault: 0000 [#1] PREEMPT SMP PTI **snip** Call Trace: lock_acquire+0xa2/0x1b0 _raw_spin_lock_irq+0x39/0x70 wait_for_completion_timeout+0x31/0x130 drm_atomic_helper_wait_for_flip_done+0x64/0x90 [drm_kms_helper] amdgpu_dm_atomic_commit_tail+0xcae/0xdd0 [amdgpu] commit_tail+0x3d/0x70 [drm_kms_helper] process_one_work+0x212/0x650 worker_thread+0x49/0x420 kthread+0xfb/0x130 ret_from_fork+0x3a/0x50 Modules linked in: x86_pkg_temp_thermal amdgpu(O) chash(O) gpu_sched(O) drm_kms_helper(O) syscopyarea sysfillrect sysimgblt fb_sys_fops ttm(O) drm(O) Note that i915 has this issue masked, since hw_done is signaled after waiting for flip_done. Doing so will block the cursor update from happening until hw_done is signaled, preventing the cursor commit from destroying the state. v2: The reference on the commit object needs to be obtained before hw_done() is signaled, since that's the point where another commit is allowed to modify the state. Assuming that the new_crtc_state->commit object still exists within flip_done() is incorrect. Fix by getting a reference in setup_commit(), and releasing it during default_clear(). Signed-off-by: Leo Li <sunpeng.li@amd.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Harry Wentland <harry.wentland@amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/1539611200-6184-1-git-send-email-sunpeng.li@amd.com
3 files changed, 24 insertions, 4 deletions
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 018fcdb353d2..281cf9cbb44c 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -174,6 +174,11 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
state->crtcs[i].state = NULL;
state->crtcs[i].old_state = NULL;
state->crtcs[i].new_state = NULL;
+ if (state->crtcs[i].commit) {
+ drm_crtc_commit_put(state->crtcs[i].commit);
+ state->crtcs[i].commit = NULL;
+ }
for (i = 0; i < config->num_total_plane; i++) {
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 80be74df7ba6..1bb4c318bdd4 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1408,15 +1408,16 @@ EXPORT_SYMBOL(drm_atomic_helper_wait_for_vblanks);
void drm_atomic_helper_wait_for_flip_done(struct drm_device *dev,
struct drm_atomic_state *old_state)
- struct drm_crtc_state *new_crtc_state;
struct drm_crtc *crtc;
int i;
- for_each_new_crtc_in_state(old_state, crtc, new_crtc_state, i) {
- struct drm_crtc_commit *commit = new_crtc_state->commit;
+ for (i = 0; i < dev->mode_config.num_crtc; i++) {
+ struct drm_crtc_commit *commit = old_state->crtcs[i].commit;
int ret;
- if (!commit)
+ crtc = old_state->crtcs[i].ptr;
+ if (!crtc || !commit)
ret = wait_for_completion_timeout(&commit->flip_done, 10 * HZ);
@@ -1934,6 +1935,9 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
commit->abort_completion = true;
+ state->crtcs[i].commit = commit;
+ drm_crtc_commit_get(commit);
for_each_oldnew_connector_in_state(state, conn, old_conn_state, new_conn_state, i) {
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index da9d95a19580..1e713154f00e 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -153,6 +153,17 @@ struct __drm_planes_state {
struct __drm_crtcs_state {
struct drm_crtc *ptr;
struct drm_crtc_state *state, *old_state, *new_state;
+ /**
+ * @commit:
+ *
+ * A reference to the CRTC commit object that is kept for use by
+ * drm_atomic_helper_wait_for_flip_done() after
+ * drm_atomic_helper_commit_hw_done() is called. This ensures that a
+ * concurrent commit won't free a commit object that is still in use.
+ */
+ struct drm_crtc_commit *commit;
s32 __user *out_fence_ptr;
u64 last_vblank_count;