drm/xe: Remove unwanted mutex locking

Do not hold xef->exec_queue.lock mutex while parsing the xarray
xef->exec_queue.xa in xe_file_close() as it is not needed and
will cause an unwanted dependency between this lock and the vm->lock.

This lock protects the exec queue lookup and reference taking which
doesn't apply to this code path. When FD is closing, IOCTLs presumably
can't be modifying the xarray.

v2: Update commit text (Matt Brost)
v3: Add more code comment (Rodrigo Vivi)
v4: Further expand code comment (Rodirgo Vivi)

Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jagmeet Randhawa <jagmeet.randhawa@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240529221639.23117-1-niranjana.vishwanathapura@intel.com

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index b2d5c7341238e07a832d8a7ec6bedc32610cc400..d1560f5d4b8480b17f3af6eda85eef7cf9b124f8 100644 (file)
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -95,12 +95,16 @@ static void xe_file_close(struct drm_device *dev, struct drm_file *file)
        struct xe_exec_queue *q;
        unsigned long idx;
 
-       mutex_lock(&xef->exec_queue.lock);
+       /*
+        * No need for exec_queue.lock here as there is no contention for it
+        * when FD is closing as IOCTLs presumably can't be modifying the
+        * xarray. Taking exec_queue.lock here causes undue dependency on
+        * vm->lock taken during xe_exec_queue_kill().
+        */
        xa_for_each(&xef->exec_queue.xa, idx, q) {
                xe_exec_queue_kill(q);
                xe_exec_queue_put(q);
        }
-       mutex_unlock(&xef->exec_queue.lock);
        xa_destroy(&xef->exec_queue.xa);
        mutex_destroy(&xef->exec_queue.lock);
        mutex_lock(&xef->vm.lock);