On Tue, Oct 16, 2018 at 11:00 AM Li, Sun peng (Leo) <Sunpeng.Li@xxxxxxx> wrote: > > > > 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. Leo, do you or Harry have drm-misc commit access yet? If not, you should. Alex > > > > 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 > >> > > > _______________________________________________ > amd-gfx mailing list > amd-gfx@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/amd-gfx _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
