[PATCH v2] drm: Get ref on CRTC commit object when waiting for flip_done
Wentland, Harry
Harry.Wentland at amd.com
Thu Oct 18 18:48:15 UTC 2018
On 2018-10-18 1:38 p.m., Wentland, Harry wrote:
> On 2018-10-16 11:48 a.m., Alex Deucher wrote:
>> On Tue, Oct 16, 2018 at 11:00 AM Li, Sun peng (Leo) <Sunpeng.Li at amd.com> wrote:
>>>
>>>
>>>
>>> On 2018-10-16 08:33 AM, Daniel Vetter wrote:
>>>> On Mon, Oct 15, 2018 at 09:46:40AM -0400, sunpeng.li at amd.com wrote:
>>>>> From: Leo Li <sunpeng.li at amd.com>
>>>>>
>>>>> 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 at amd.com>
>>>>> ---
>>>>>
>>>>> Sending again, this time to the correct mailing list :)
>>>>>
>>>>> Leo
>>>>
>>>> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>> Cc: stable at vger.kernel.org
>>>>
>>>> I think it'd be really good if you could get intel-gfx-ci to test this
>>>> patch. Simply submit it to intel-gfx at lists.freedesktop.org. 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.
>>
>
> I believe I do and will push the patch. Leo's getting the ball rolling to get access (fdo account, etc).
>
... and pushed to drm-misc-fixes.
Harry
> Harry
>
>> 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 at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
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