drm/i915: Don't disable interrupts and pretend a lock as been acquired in __timeline_...

This is a revert of commits
   d67739268cf0e ("drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe")
   6c69a45445af9 ("drm/i915/gt: Mark context->active_count as protected by timeline->mutex")
   6dcb85a0ad990 ("drm/i915: Hold irq-off for the entire fake lock period")

The existing code leads to a different behaviour depending on whether
lockdep is enabled or not. Any following lock that is acquired without
disabling interrupts (but needs to) will not be noticed by lockdep.

This it not just a lockdep annotation but is used but an actual mutex_t
that is properly used as a lock but in case of __timeline_mark_lock()
lockdep is only told that it is acquired but no lock has been acquired.

It appears that its purpose is just satisfy the lockdep_assert_held()
check in intel_context_mark_active(). The other problem with disabling
interrupts is that on PREEMPT_RT interrupts are also disabled which
leads to problems for instance later during memory allocation.

Add a CONTEXT_IS_PARKING bit to intel_engine_cs and set_bit/clear_bit it
instead of mutex_acquire/mutex_release. Use test_bit in the two
identified spots which relied on the lockdep annotation.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/YbO8Ie1Nj7XcQPNQ@linutronix.de

diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
index 246c37d72cd73656efc6d1eda5d8488689eb8eff..d8c74bbf9aae2bd80358c907af868ea95b0757da 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_context.h
+++ b/drivers/gpu/drm/i915/gt/intel_context.h
@@ -211,7 +211,8 @@ static inline void intel_context_enter(struct intel_context *ce)
 
 static inline void intel_context_mark_active(struct intel_context *ce)
 {
-       lockdep_assert_held(&ce->timeline->mutex);
+       lockdep_assert(lockdep_is_held(&ce->timeline->mutex) ||
+                      test_bit(CONTEXT_IS_PARKING, &ce->flags));
        ++ce->active_count;
 }
 

diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
index 9e0177dc5484e6c36d10c21b23769f27eef4c9a4..30cd81ad8911a1fc98bc14f460fc223035b44e60 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
@@ -118,6 +118,7 @@ struct intel_context {
 #define CONTEXT_LRCA_DIRTY             9
 #define CONTEXT_GUC_INIT               10
 #define CONTEXT_PERMA_PIN              11
+#define CONTEXT_IS_PARKING             12
 
        struct {
                u64 timeout_us;

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index a1334b48dde7be7f309ac4c599c0675079dc7866..a8a2ad44b7e3972ad45d065fb28bac2f7c91ec38 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -80,39 +80,6 @@ static int __engine_unpark(struct intel_wakeref *wf)
        return 0;
 }
 
-#if IS_ENABLED(CONFIG_LOCKDEP)
-
-static unsigned long __timeline_mark_lock(struct intel_context *ce)
-{
-       unsigned long flags;
-
-       local_irq_save(flags);
-       mutex_acquire(&ce->timeline->mutex.dep_map, 2, 0, _THIS_IP_);
-
-       return flags;
-}
-
-static void __timeline_mark_unlock(struct intel_context *ce,
-                                  unsigned long flags)
-{
-       mutex_release(&ce->timeline->mutex.dep_map, _THIS_IP_);
-       local_irq_restore(flags);
-}
-
-#else
-
-static unsigned long __timeline_mark_lock(struct intel_context *ce)
-{
-       return 0;
-}
-
-static void __timeline_mark_unlock(struct intel_context *ce,
-                                  unsigned long flags)
-{
-}
-
-#endif /* !IS_ENABLED(CONFIG_LOCKDEP) */
-
 static void duration(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
        struct i915_request *rq = to_request(fence);
@@ -159,7 +126,6 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 {
        struct intel_context *ce = engine->kernel_context;
        struct i915_request *rq;
-       unsigned long flags;
        bool result = true;
 
        /*
@@ -214,7 +180,7 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
         * engine->wakeref.count, we may see the request completion and retire
         * it causing an underflow of the engine->wakeref.
         */
-       flags = __timeline_mark_lock(ce);
+       set_bit(CONTEXT_IS_PARKING, &ce->flags);
        GEM_BUG_ON(atomic_read(&ce->timeline->active_count) < 0);
 
        rq = __i915_request_create(ce, GFP_NOWAIT);
@@ -246,7 +212,7 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 
        result = false;
 out_unlock:
-       __timeline_mark_unlock(ce, flags);
+       clear_bit(CONTEXT_IS_PARKING, &ce->flags);
        return result;
 }
 

diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index 0ed01979491b5801f2ff05eda0a5e9e36cc5d7df..ce771421069773981737e2f467938ee0888a9216 100644 (file)
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -657,7 +657,8 @@ i915_request_timeline(const struct i915_request *rq)
 {
        /* Valid only while the request is being constructed (or retired). */
        return rcu_dereference_protected(rq->timeline,
-                                        lockdep_is_held(&rcu_access_pointer(rq->timeline)->mutex));
+                                        lockdep_is_held(&rcu_access_pointer(rq->timeline)->mutex) ||
+                                        test_bit(CONTEXT_IS_PARKING, &rq->context->flags));
 }
 
 static inline struct i915_gem_context *