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authorDave Airlie <airlied@redhat.com>2020-09-18 08:37:31 +1000
committerDave Airlie <airlied@redhat.com>2020-09-18 08:37:31 +1000
commitd7261b14ddc79b665acdc5fcad8eaf988e0025a8 (patch)
treeb78c596e014cbc155e8ad374b9a31a910e7dedfc /drivers/gpu/drm
parent4b1ededb69d930a9f904be0a5320f4f3e74f9f13 (diff)
parent20612303a0b45de748d31331407e84300c38e497 (diff)
downloadlinux-d7261b14ddc79b665acdc5fcad8eaf988e0025a8.tar.bz2
Merge tag 'drm-intel-fixes-2020-09-17' of ssh://git.freedesktop.org/git/drm/drm-intel into drm-fixes
drm/i915 fixes for v5.9-rc6: - Avoid exposing a partially constructed context - Use RCU instead of mutex for context termination list iteration - Avoid data race reported by KCSAN - Filter wake_flags passed to default_wake_function Signed-off-by: Dave Airlie <airlied@redhat.com> From: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/87y2l8vlj3.fsf@intel.com
Diffstat (limited to 'drivers/gpu/drm')
-rw-r--r--drivers/gpu/drm/i915/gem/i915_gem_context.c48
-rw-r--r--drivers/gpu/drm/i915/gt/intel_lrc.c15
-rw-r--r--drivers/gpu/drm/i915/i915_request.c25
-rw-r--r--drivers/gpu/drm/i915/i915_sw_fence.c10
4 files changed, 71 insertions, 27 deletions
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index d0bdb6d447ed..ef755dd5e68f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -439,29 +439,36 @@ static bool __cancel_engine(struct intel_engine_cs *engine)
return __reset_engine(engine);
}
-static struct intel_engine_cs *__active_engine(struct i915_request *rq)
+static bool
+__active_engine(struct i915_request *rq, struct intel_engine_cs **active)
{
struct intel_engine_cs *engine, *locked;
+ bool ret = false;
/*
* Serialise with __i915_request_submit() so that it sees
* is-banned?, or we know the request is already inflight.
+ *
+ * Note that rq->engine is unstable, and so we double
+ * check that we have acquired the lock on the final engine.
*/
locked = READ_ONCE(rq->engine);
spin_lock_irq(&locked->active.lock);
while (unlikely(locked != (engine = READ_ONCE(rq->engine)))) {
spin_unlock(&locked->active.lock);
- spin_lock(&engine->active.lock);
locked = engine;
+ spin_lock(&locked->active.lock);
}
- engine = NULL;
- if (i915_request_is_active(rq) && rq->fence.error != -EIO)
- engine = rq->engine;
+ if (!i915_request_completed(rq)) {
+ if (i915_request_is_active(rq) && rq->fence.error != -EIO)
+ *active = locked;
+ ret = true;
+ }
spin_unlock_irq(&locked->active.lock);
- return engine;
+ return ret;
}
static struct intel_engine_cs *active_engine(struct intel_context *ce)
@@ -472,17 +479,16 @@ static struct intel_engine_cs *active_engine(struct intel_context *ce)
if (!ce->timeline)
return NULL;
- mutex_lock(&ce->timeline->mutex);
- list_for_each_entry_reverse(rq, &ce->timeline->requests, link) {
- if (i915_request_completed(rq))
- break;
+ rcu_read_lock();
+ list_for_each_entry_rcu(rq, &ce->timeline->requests, link) {
+ if (i915_request_is_active(rq) && i915_request_completed(rq))
+ continue;
/* Check with the backend if the request is inflight */
- engine = __active_engine(rq);
- if (engine)
+ if (__active_engine(rq, &engine))
break;
}
- mutex_unlock(&ce->timeline->mutex);
+ rcu_read_unlock();
return engine;
}
@@ -713,6 +719,7 @@ __create_context(struct drm_i915_private *i915)
ctx->i915 = i915;
ctx->sched.priority = I915_USER_PRIORITY(I915_PRIORITY_NORMAL);
mutex_init(&ctx->mutex);
+ INIT_LIST_HEAD(&ctx->link);
spin_lock_init(&ctx->stale.lock);
INIT_LIST_HEAD(&ctx->stale.engines);
@@ -740,10 +747,6 @@ __create_context(struct drm_i915_private *i915)
for (i = 0; i < ARRAY_SIZE(ctx->hang_timestamp); i++)
ctx->hang_timestamp[i] = jiffies - CONTEXT_FAST_HANG_JIFFIES;
- spin_lock(&i915->gem.contexts.lock);
- list_add_tail(&ctx->link, &i915->gem.contexts.list);
- spin_unlock(&i915->gem.contexts.lock);
-
return ctx;
err_free:
@@ -931,6 +934,7 @@ static int gem_context_register(struct i915_gem_context *ctx,
struct drm_i915_file_private *fpriv,
u32 *id)
{
+ struct drm_i915_private *i915 = ctx->i915;
struct i915_address_space *vm;
int ret;
@@ -949,8 +953,16 @@ static int gem_context_register(struct i915_gem_context *ctx,
/* And finally expose ourselves to userspace via the idr */
ret = xa_alloc(&fpriv->context_xa, id, ctx, xa_limit_32b, GFP_KERNEL);
if (ret)
- put_pid(fetch_and_zero(&ctx->pid));
+ goto err_pid;
+
+ spin_lock(&i915->gem.contexts.lock);
+ list_add_tail(&ctx->link, &i915->gem.contexts.list);
+ spin_unlock(&i915->gem.contexts.lock);
+
+ return 0;
+err_pid:
+ put_pid(fetch_and_zero(&ctx->pid));
return ret;
}
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 24322ef08aa4..9eeaca957a7e 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2060,6 +2060,14 @@ static inline void clear_ports(struct i915_request **ports, int count)
memset_p((void **)ports, NULL, count);
}
+static inline void
+copy_ports(struct i915_request **dst, struct i915_request **src, int count)
+{
+ /* A memcpy_p() would be very useful here! */
+ while (count--)
+ WRITE_ONCE(*dst++, *src++); /* avoid write tearing */
+}
+
static void execlists_dequeue(struct intel_engine_cs *engine)
{
struct intel_engine_execlists * const execlists = &engine->execlists;
@@ -2648,10 +2656,9 @@ static void process_csb(struct intel_engine_cs *engine)
/* switch pending to inflight */
GEM_BUG_ON(!assert_pending_valid(execlists, "promote"));
- memcpy(execlists->inflight,
- execlists->pending,
- execlists_num_ports(execlists) *
- sizeof(*execlists->pending));
+ copy_ports(execlists->inflight,
+ execlists->pending,
+ execlists_num_ports(execlists));
smp_wmb(); /* complete the seqlock */
WRITE_ONCE(execlists->active, execlists->inflight);
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 0b2fe55e6194..781a6783affe 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -388,17 +388,38 @@ static bool __request_in_flight(const struct i915_request *signal)
* As we know that there are always preemption points between
* requests, we know that only the currently executing request
* may be still active even though we have cleared the flag.
- * However, we can't rely on our tracking of ELSP[0] to known
+ * However, we can't rely on our tracking of ELSP[0] to know
* which request is currently active and so maybe stuck, as
* the tracking maybe an event behind. Instead assume that
* if the context is still inflight, then it is still active
* even if the active flag has been cleared.
+ *
+ * To further complicate matters, if there a pending promotion, the HW
+ * may either perform a context switch to the second inflight execlists,
+ * or it may switch to the pending set of execlists. In the case of the
+ * latter, it may send the ACK and we process the event copying the
+ * pending[] over top of inflight[], _overwriting_ our *active. Since
+ * this implies the HW is arbitrating and not struck in *active, we do
+ * not worry about complete accuracy, but we do require no read/write
+ * tearing of the pointer [the read of the pointer must be valid, even
+ * as the array is being overwritten, for which we require the writes
+ * to avoid tearing.]
+ *
+ * Note that the read of *execlists->active may race with the promotion
+ * of execlists->pending[] to execlists->inflight[], overwritting
+ * the value at *execlists->active. This is fine. The promotion implies
+ * that we received an ACK from the HW, and so the context is not
+ * stuck -- if we do not see ourselves in *active, the inflight status
+ * is valid. If instead we see ourselves being copied into *active,
+ * we are inflight and may signal the callback.
*/
if (!intel_context_inflight(signal->context))
return false;
rcu_read_lock();
- for (port = __engine_active(signal->engine); (rq = *port); port++) {
+ for (port = __engine_active(signal->engine);
+ (rq = READ_ONCE(*port)); /* may race with promotion of pending[] */
+ port++) {
if (rq->context == signal->context) {
inflight = i915_seqno_passed(rq->fence.seqno,
signal->fence.seqno);
diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
index 295b9829e2da..4cd2038cbe35 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence.c
+++ b/drivers/gpu/drm/i915/i915_sw_fence.c
@@ -164,9 +164,13 @@ static void __i915_sw_fence_wake_up_all(struct i915_sw_fence *fence,
do {
list_for_each_entry_safe(pos, next, &x->head, entry) {
- pos->func(pos,
- TASK_NORMAL, fence->error,
- &extra);
+ int wake_flags;
+
+ wake_flags = fence->error;
+ if (pos->func == autoremove_wake_function)
+ wake_flags = 0;
+
+ pos->func(pos, TASK_NORMAL, wake_flags, &extra);
}
if (list_empty(&extra))