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drm/i915: Fix ref->mutex deadlock in i915_active_wait()

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The following deadlock exists in i915_active_wait() due to a double lock
on ref->mutex (call chain listed in order from top to bottom):
 i915_active_wait();
 mutex_lock_interruptible(&ref->mutex); <-- ref->mutex first acquired
 i915_active_request_retire();
 node_retire();
 active_retire();
 mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); <-- DEADLOCK

Fix the deadlock by skipping the second ref->mutex lock when
active_retire() is called through i915_active_request_retire().

Note that this bug only affects 5.4 and has since been fixed in 5.5.
Normally, a backport of the fix from 5.5 would be in order, but the
patch set that fixes this deadlock involves massive changes that are
neither feasible nor desirable for backporting [1][2][3]. Therefore,
this small patch was made to address the deadlock specifically for 5.4.

[1] 274cbf20fd10 ("drm/i915: Push the i915_active.retire into a worker")
[2] 093b92287363 ("drm/i915: Split i915_active.mutex into an irq-safe spinlock for the rbtree")
[3] 750bde2fd4ff ("drm/i915: Serialise with remote retirement")

Fixes: 12c255b5dad1 ("drm/i915: Provide an i915_active.acquire callback")
Cc: <stable@vger.kernel.org> # 5.4.x
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sultan Alsawaf 2020-04-07 13:32:22 -07:00 committed by Greg Kroah-Hartman
parent 047affa0ef
commit 04ad505eed
2 changed files with 21 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
drivers/gpu/drm/i915/i915_active.c
View File

@ -121,7 +121,7 @@ static inline void debug_active_assert(struct i915_active *ref) { }
#endif
static void
__active_retire(struct i915_active *ref)
__active_retire(struct i915_active *ref, bool lock)
{
struct active_node *it, *n;
struct rb_root root;
@ -138,7 +138,8 @@ __active_retire(struct i915_active *ref)
retire = true;
}
mutex_unlock(&ref->mutex);
if (likely(lock))
mutex_unlock(&ref->mutex);
if (!retire)
return;
@ -153,21 +154,28 @@ __active_retire(struct i915_active *ref)
}
static void
active_retire(struct i915_active *ref)
active_retire(struct i915_active *ref, bool lock)
{
GEM_BUG_ON(!atomic_read(&ref->count));
if (atomic_add_unless(&ref->count, -1, 1))
return;
/* One active may be flushed from inside the acquire of another */
mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING);
__active_retire(ref);
if (likely(lock))
mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING);
__active_retire(ref, lock);
}
static void
node_retire(struct i915_active_request *base, struct i915_request *rq)
{
active_retire(node_from_active(base)->ref);
active_retire(node_from_active(base)->ref, true);
}
static void
node_retire_nolock(struct i915_active_request *base, struct i915_request *rq)
{
active_retire(node_from_active(base)->ref, false);
}
static struct i915_active_request *
@ -364,7 +372,7 @@ int i915_active_acquire(struct i915_active *ref)
void i915_active_release(struct i915_active *ref)
{
debug_active_assert(ref);
active_retire(ref);
active_retire(ref, true);
}
static void __active_ungrab(struct i915_active *ref)
@ -391,7 +399,7 @@ void i915_active_ungrab(struct i915_active *ref)
{
GEM_BUG_ON(!test_bit(I915_ACTIVE_GRAB_BIT, &ref->flags));
active_retire(ref);
active_retire(ref, true);
__active_ungrab(ref);
}
@ -421,12 +429,13 @@ int i915_active_wait(struct i915_active *ref)
break;
}
err = i915_active_request_retire(&it->base, BKL(ref));
err = i915_active_request_retire(&it->base, BKL(ref),
node_retire_nolock);
if (err)
break;
}
__active_retire(ref);
__active_retire(ref, true);
if (err)
return err;

4
drivers/gpu/drm/i915/i915_active.h
View File

@ -309,7 +309,7 @@ i915_active_request_isset(const struct i915_active_request *active)
*/
static inline int __must_check
i915_active_request_retire(struct i915_active_request *active,
struct mutex *mutex)
struct mutex *mutex, i915_active_retire_fn retire)
{
struct i915_request *request;
long ret;
@ -327,7 +327,7 @@ i915_active_request_retire(struct i915_active_request *active,
list_del_init(&active->link);
RCU_INIT_POINTER(active->request, NULL);
active->retire(active, request);
retire(active, request);
return 0;
}