drm/i915/guc: Don't deadlock busyness stats vs reset

The engine busyness stats has a worker function to do things like
64bit extend the 32bit hardware counters. The GuC's reset prepare
function flushes out this worker function to ensure no corruption
happens during the reset. Unforunately, the worker function has an
infinite wait for active resets to finish before doing its work. Thus
a deadlock would occur if the worker function had actually started
just as the reset starts.

The function being used to lock the reset-in-progress mutex is called
intel_gt_reset_trylock(). However, as noted it does not follow
standard 'trylock' conventions and exit if already locked. So rename
the current _trylock function to intel_gt_reset_lock_interruptible(),
which is the behaviour it actually provides. In addition, add a new
implementation of _trylock and call that from the busyness stats
worker instead.

v2: Rename existing trylock to interruptible rather than trying to
preserve the existing (confusing) naming scheme (review comments from
Tvrtko).

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221102192109.2492625-3-John.C.Harrison@Intel.com

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index e63329bc80659cae184e66ed3f13755e044e0c84..c29efdef8313a5acffef16332d6cf261f4ad395e 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -330,7 +330,7 @@ retry:
        if (ret)
                goto err_rpm;
 
-       ret = intel_gt_reset_trylock(ggtt->vm.gt, &srcu);
+       ret = intel_gt_reset_lock_interruptible(ggtt->vm.gt, &srcu);
        if (ret)
                goto err_pages;
 

diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
index 3159df6cdd492f7b651be0acfa669e2033fa037a..24736ebee17c286758c81311846ed35c5dc9d869 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_reset.c
+++ b/drivers/gpu/drm/i915/gt/intel_reset.c
@@ -1407,15 +1407,19 @@ out:
        intel_runtime_pm_put(gt->uncore->rpm, wakeref);
 }
 
-int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu)
+static int _intel_gt_reset_lock(struct intel_gt *gt, int *srcu, bool retry)
 {
        might_lock(&gt->reset.backoff_srcu);
-       might_sleep();
+       if (retry)
+               might_sleep();
 
        rcu_read_lock();
        while (test_bit(I915_RESET_BACKOFF, &gt->reset.flags)) {
                rcu_read_unlock();
 
+               if (!retry)
+                       return -EBUSY;
+
                if (wait_event_interruptible(gt->reset.queue,
                                             !test_bit(I915_RESET_BACKOFF,
                                                       &gt->reset.flags)))
@@ -1429,6 +1433,16 @@ int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu)
        return 0;
 }
 
+int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu)
+{
+       return _intel_gt_reset_lock(gt, srcu, false);
+}
+
+int intel_gt_reset_lock_interruptible(struct intel_gt *gt, int *srcu)
+{
+       return _intel_gt_reset_lock(gt, srcu, true);
+}
+
 void intel_gt_reset_unlock(struct intel_gt *gt, int tag)
 __releases(&gt->reset.backoff_srcu)
 {

diff --git a/drivers/gpu/drm/i915/gt/intel_reset.h b/drivers/gpu/drm/i915/gt/intel_reset.h
index adc734e6738700568b53e4cc7673fc74d1758023..25c975b6e8fc01db398cba1dc09f9bb12b3a86bd 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_reset.h
+++ b/drivers/gpu/drm/i915/gt/intel_reset.h
@@ -39,6 +39,7 @@ int __intel_engine_reset_bh(struct intel_engine_cs *engine,
 void __i915_request_reset(struct i915_request *rq, bool guilty);
 
 int __must_check intel_gt_reset_trylock(struct intel_gt *gt, int *srcu);
+int __must_check intel_gt_reset_lock_interruptible(struct intel_gt *gt, int *srcu);
 void intel_gt_reset_unlock(struct intel_gt *gt, int tag);
 
 void intel_gt_set_wedged(struct intel_gt *gt);

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 8fbc363564607195f7747d03d3fcbace4966326c..412c2624e11900528d5446798eed816a2fd63bfb 100644 (file)
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1401,7 +1401,9 @@ static void guc_timestamp_ping(struct work_struct *wrk)
 
        /*
         * Synchronize with gt reset to make sure the worker does not
-        * corrupt the engine/guc stats.
+        * corrupt the engine/guc stats. NB: can't actually block waiting
+        * for a reset to complete as the reset requires flushing out
+        * this worker thread if started. So waiting would deadlock.
         */
        ret = intel_gt_reset_trylock(gt, &srcu);
        if (ret)