4.18-stable review patch. If anyone has any objections, please let me know.
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From: Leo Li sunpeng.li@amd.com
[ Upstream commit 4364bcb2cd21d042bde4776448417ddffbc54045 ]
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-ema... Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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(-)
--- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -173,6 +173,11 @@ void drm_atomic_state_default_clear(stru 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++) { --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -1384,15 +1384,16 @@ EXPORT_SYMBOL(drm_atomic_helper_wait_for 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); @@ -1906,6 +1907,9 @@ int drm_atomic_helper_setup_commit(struc 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) { --- 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; };