On 2018-10-16 08:33 AM, Daniel Vetter wrote: > On Mon, Oct 15, 2018 at 09:46:40AM -0400, sunpeng.li@xxxxxxx wrote: >> From: Leo Li <sunpeng.li@xxxxxxx> >> >> 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@xxxxxxx> >> --- >> >> Sending again, this time to the correct mailing list :) >> >> Leo > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > > I think it'd be really good if you could get intel-gfx-ci to test this > patch. Simply submit it to intel-gfx@xxxxxxxxxxxxxxxxxxxxx. I'll leave > applying to one of the amd drm-misc committers, once it's passed CI. > > Cheers, Daniel Thanks for the rb! On the topic of CI, is it possible to write a test (maybe one already exists) for this issue? I've attempted to do one here: https://patchwork.freedesktop.org/patch/256319/ The problem is finding a surefire way to trigger the sequence, I'm not sure how that can be done. If you have any ideas, I would love to hear them. Leo > >> >> drivers/gpu/drm/drm_atomic.c | 5 +++++ >> drivers/gpu/drm/drm_atomic_helper.c | 12 ++++++++---- >> include/drm/drm_atomic.h | 11 +++++++++++ >> 3 files changed, 24 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c >> index 3eb061e..12ae917 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 80be74d..1bb4c31 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) >> continue; >> >> 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, >> drm_crtc_commit_get(commit); >> >> 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 da9d95a..1e71315 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; >> }; >> -- >> 2.7.4 >> > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
