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 <sta...@vger.kernel.org> know about it.
>From sul...@kerneltoast.com Sat Apr 11 13:39:11 2020
From: Sultan Alsawaf <sul...@kerneltoast.com>
Date: Tue, 7 Apr 2020 13:32:22 -0700
Subject: drm/i915: Fix ref->mutex deadlock in i915_active_wait()
To: sta...@vger.kernel.org
Cc: Greg KH <g...@kroah.com>, Jani Nikula <jani.nik...@linux.intel.com>, Joonas
Lahtinen <joonas.lahti...@linux.intel.com>, Rodrigo Vivi
<rodrigo.v...@intel.com>, David Airlie <airl...@linux.ie>, Daniel Vetter
<dan...@ffwll.ch>, Chris Wilson <ch...@chris-wilson.co.uk>,
intel-gfx@lists.freedesktop.org, dri-de...@lists.freedesktop.org, Sultan
Alsawaf <sul...@kerneltoast.com>
Message-ID: <20200407203222.2493-1-sul...@kerneltoast.com>
From: Sultan Alsawaf <sul...@kerneltoast.com>
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: <sta...@vger.kernel.org> # 5.4.x
Signed-off-by: Sultan Alsawaf <sul...@kerneltoast.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/gpu/drm/i915/i915_active.c | 29 +++++++++++++++++++----------
drivers/gpu/drm/i915/i915_active.h | 4 ++--
2 files changed, 21 insertions(+), 12 deletions(-)
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -121,7 +121,7 @@ static inline void debug_active_assert(s
#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_acti
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_acti
{
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
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;
--- 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 sul...@kerneltoast.com are
queue-5.4/drm-i915-fix-ref-mutex-deadlock-in-i915_active_wait.patch
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