This is a note to let you know that I've just added the patch titled
drm/i915: Fix ref->mutex deadlock in i915_active_wait()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-i915-fix-ref-mutex-deadlock-in-i915_active_wait.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From sultan@xxxxxxxxxxxxxxx Fri Apr 10 11:07:34 2020
From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
Date: Tue, 7 Apr 2020 00:18:09 -0700
Subject: drm/i915: Fix ref->mutex deadlock in i915_active_wait()
To: Greg KH <greg@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>, Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>, Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>, David Airlie <airlied@xxxxxxxx>, Daniel Vetter <daniel@xxxxxxxx>, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>, intel-gfx@xxxxxxxxxxxxxxxxxxxxx, dri-devel@xxxxxxxxxxxxxxxxxxxxx, Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
Message-ID: <20200407071809.3148-1-sultan@xxxxxxxxxxxxxxx>
From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx> # 5.4.x
Signed-off-by: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_active.c | 27 +++++++++++++++++++++++----
drivers/gpu/drm/i915/i915_active.h | 4 ++--
2 files changed, 25 insertions(+), 6 deletions(-)
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -120,13 +120,17 @@ static inline void debug_active_assert(s
#endif
+#define I915_ACTIVE_RETIRE_NOLOCK BIT(0)
+
static void
__active_retire(struct i915_active *ref)
{
struct active_node *it, *n;
struct rb_root root;
bool retire = false;
+ unsigned long bits;
+ ref = ptr_unpack_bits(ref, &bits, 2);
lockdep_assert_held(&ref->mutex);
/* return the unused nodes to our slabcache -- flushing the allocator */
@@ -138,7 +142,8 @@ __active_retire(struct i915_active *ref)
retire = true;
}
- mutex_unlock(&ref->mutex);
+ if (!(bits & I915_ACTIVE_RETIRE_NOLOCK))
+ mutex_unlock(&ref->mutex);
if (!retire)
return;
@@ -155,13 +160,18 @@ __active_retire(struct i915_active *ref)
static void
active_retire(struct i915_active *ref)
{
+ struct i915_active *ref_packed = ref;
+ unsigned long bits;
+
+ ref = ptr_unpack_bits(ref, &bits, 2);
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 (!(bits & I915_ACTIVE_RETIRE_NOLOCK))
+ mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING);
+ __active_retire(ref_packed);
}
static void
@@ -170,6 +180,14 @@ node_retire(struct i915_active_request *
active_retire(node_from_active(base)->ref);
}
+static void
+node_retire_nolock(struct i915_active_request *base, struct i915_request *rq)
+{
+ struct i915_active *ref = node_from_active(base)->ref;
+
+ active_retire(ptr_pack_bits(ref, I915_ACTIVE_RETIRE_NOLOCK, 2));
+}
+
static struct i915_active_request *
active_instance(struct i915_active *ref, struct intel_timeline *tl)
{
@@ -421,7 +439,8 @@ int i915_active_wait(struct i915_active
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;
}
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -309,7 +309,7 @@ i915_active_request_isset(const struct i
*/
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_a
list_del_init(&active->link);
RCU_INIT_POINTER(active->request, NULL);
- active->retire(active, request);
+ retire(active, request);
return 0;
}
Patches currently in stable-queue which might be from sultan@xxxxxxxxxxxxxxx are
queue-5.4/drm-i915-fix-ref-mutex-deadlock-in-i915_active_wait.patch
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