On 12/06/2020 15:55, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2020-06-12 15:44:51)
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
As per our locking rules it is not allowed to wait on requests while
holding locks. In this case we were trying to idle the GPU while holding
the vm->mutex.
Synchronous eviction would like to have a word.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/selftests/i915_gem_evict.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
index 028baae9631f..67f4497c8224 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_evict.c
@@ -498,8 +498,6 @@ static int igt_evict_contexts(void *arg)
mutex_lock(&ggtt->vm.mutex);
out_locked:
- if (igt_flush_test(i915))
- err = -EIO;
while (reserved) {
struct reserved *next = reserved->next;
@@ -513,6 +511,9 @@ static int igt_evict_contexts(void *arg)
mutex_unlock(&ggtt->vm.mutex);
intel_runtime_pm_put(&i915->runtime_pm, wakeref);
+ if (igt_flush_test(i915))
+ err = -EIO;
The patch is ok, since the manual drm_mm_node reservations are not used
by the GTT, but the reason is a bit specious.
We have a comment in i915_request_wait which says:
/*
* We must never wait on the GPU while holding a lock as we
* may need to perform a GPU reset. So while we don't need to
* serialise wait/reset with an explicit lock, we do want
* lockdep to detect potential dependency cycles.
*/
And then there was a lockdep splat here
https://intel-gfx-ci.01.org/tree/drm-tip/Trybot_6595/fi-skl-6700k2/igt@i915_selftest@live@xxxxxxxxxx,
which although uses some extra lockdep annotation patches, seemed to
connect the two:
<4> [258.014638] Chain exists of:
>->reset.mutex --> fs_reclaim --> &vm->mutex
<4> [258.014640] Possible unsafe locking scenario:
<4> [258.014641] CPU0 CPU1
<4> [258.014641] ---- ----
<4> [258.014642] lock(&vm->mutex);
<4> [258.014642] lock(fs_reclaim);
<4> [258.014643] lock(&vm->mutex);
<4> [258.014644] lock(>->reset.mutex);
<4> [258.014645]
*** DEADLOCK ***
<4> [258.014646] 2 locks held by i915_selftest/5153:
Why despite the comment in request wait it does not otherwise see this I
don't know.
Regards,
Tvrtko
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