Since we allow removing the timeline map at runtime, there is a risk
that rq->hwsp points into a stale page. To control that risk, we hold
the RCU read lock while reading *rq->hwsp, but we missed a couple of
important barriers. First, the unpinning / removal of the timeline map
must be after all RCU readers into that map are complete, i.e. after an
rcu barrier (in this case courtesy of call_rcu()). Secondly, we must
make sure that the rq->hwsp we are about to dereference under the RCU
lock is valid. In this case, we make the rq->hwsp pointer safe during
i915_request_retire() and so we know that rq->hwsp may become invalid
only after the request has been signaled. Therefore is the request is
not yet signaled when we acquire rq->hwsp under the RCU, we know that
rq->hwsp will remain valid for the duration of the RCU read lock.
This is a very small window that may lead to either considering the
request not completed (causing a delay until the request is checked
again, any wait for the request is not affected) or dereferencing an
invalid pointer.
Fixes: 3adac4689f58 ("drm/i915: Introduce concept of per-timeline (context)
HWSP")
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
Cc: <sta...@vger.kernel.org> # v5.1+
---
drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 11 ++----
drivers/gpu/drm/i915/gt/intel_timeline.c | 6 ++--
drivers/gpu/drm/i915/i915_request.h | 37 ++++++++++++++++++---
3 files changed, 39 insertions(+), 15 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 3c62fd6daa76..f96cd7d9b419 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -134,11 +134,6 @@ static bool remove_signaling_context(struct
intel_breadcrumbs *b,
return true;
}
-static inline bool __request_completed(const struct i915_request *rq)
-{
- return i915_seqno_passed(__hwsp_seqno(rq), rq->fence.seqno);
-}
-
__maybe_unused static bool
check_signal_order(struct intel_context *ce, struct i915_request *rq)
{
@@ -245,7 +240,7 @@ static void signal_irq_work(struct irq_work *work)
list_for_each_entry_rcu(rq, &ce->signals, signal_link) {
bool release;
- if (!__request_completed(rq))
+ if (!__i915_request_is_complete(rq))
break;
if (!test_and_clear_bit(I915_FENCE_FLAG_SIGNAL,
@@ -380,7 +375,7 @@ static void insert_breadcrumb(struct i915_request *rq)
* straight onto a signaled list, and queue the irq worker for
* its signal completion.
*/
- if (__request_completed(rq)) {
+ if (__i915_request_is_complete(rq)) {
irq_signal_request(rq, b);
return;
}
@@ -468,7 +463,7 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq)
if (release)
intel_context_put(ce);
- if (__request_completed(rq))
+ if (__i915_request_is_complete(rq))
irq_signal_request(rq, b);
i915_request_put(rq);
diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c
b/drivers/gpu/drm/i915/gt/intel_timeline.c
index 512afacd2bdc..a0ce2fb8737a 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline.c
+++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
@@ -126,6 +126,10 @@ static void __rcu_cacheline_free(struct rcu_head *rcu)
struct intel_timeline_cacheline *cl =
container_of(rcu, typeof(*cl), rcu);
+ /* Must wait until after all *rq->hwsp are complete before removing */
+ i915_gem_object_unpin_map(cl->hwsp->vma->obj);
+ i915_vma_put(cl->hwsp->vma);
+
i915_active_fini(&cl->active);
kfree(cl);
}
@@ -134,8 +138,6 @@ static void __idle_cacheline_free(struct
intel_timeline_cacheline *cl)
{
GEM_BUG_ON(!i915_active_is_idle(&cl->active));
- i915_gem_object_unpin_map(cl->hwsp->vma->obj);
- i915_vma_put(cl->hwsp->vma);
__idle_hwsp_free(cl->hwsp, ptr_unmask_bits(cl->vaddr, CACHELINE_BITS));
call_rcu(&cl->rcu, __rcu_cacheline_free);
diff --git a/drivers/gpu/drm/i915/i915_request.h
b/drivers/gpu/drm/i915/i915_request.h
index 92e4320c50c4..7c4453e60323 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -440,7 +440,7 @@ static inline u32 hwsp_seqno(const struct i915_request *rq)
static inline bool __i915_request_has_started(const struct i915_request *rq)
{
- return i915_seqno_passed(hwsp_seqno(rq), rq->fence.seqno - 1);
+ return i915_seqno_passed(__hwsp_seqno(rq), rq->fence.seqno - 1);
}
/**
@@ -471,11 +471,19 @@ static inline bool __i915_request_has_started(const
struct i915_request *rq)
*/
static inline bool i915_request_started(const struct i915_request *rq)
{
+ bool result;
+
if (i915_request_signaled(rq))
return true;
- /* Remember: started but may have since been preempted! */
- return __i915_request_has_started(rq);
+ result = true;
+ rcu_read_lock(); /* the HWSP may be freed at runtime */
+ if (likely(!i915_request_signaled(rq)))
+ /* Remember: started but may have since been preempted! */
+ result = __i915_request_has_started(rq);
+ rcu_read_unlock();
+
+ return result;
}
/**
@@ -488,10 +496,16 @@ static inline bool i915_request_started(const struct
i915_request *rq)
*/
static inline bool i915_request_is_running(const struct i915_request *rq)
{
+ bool result;
+
if (!i915_request_is_active(rq))
return false;
- return __i915_request_has_started(rq);
+ rcu_read_lock();
+ result = __i915_request_has_started(rq) && i915_request_is_active(rq);
+ rcu_read_unlock();
+
+ return result;
}
/**
@@ -515,12 +529,25 @@ static inline bool i915_request_is_ready(const struct
i915_request *rq)
return !list_empty(&rq->sched.link);
}
+static inline bool __i915_request_is_complete(const struct i915_request *rq)
+{
+ return i915_seqno_passed(__hwsp_seqno(rq), rq->fence.seqno);
+}
+
static inline bool i915_request_completed(const struct i915_request *rq)
{
+ bool result;
+
if (i915_request_signaled(rq))
return true;
- return i915_seqno_passed(hwsp_seqno(rq), rq->fence.seqno);
+ result = true;
+ rcu_read_lock(); /* the HWSP may be freed at runtime */
+ if (likely(!i915_request_signaled(rq)))
+ result = __i915_request_is_complete(rq);
+ rcu_read_unlock();
+
+ return result;
}
static inline void i915_request_mark_complete(struct i915_request *rq)
--
2.20.1
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