Re: [PATCH v2 04/11] drm/qxl: fix lockdep issue in qxl_alloc_release_reserved

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Am 17.02.21 um 13:32 schrieb Gerd Hoffmann:
Call qxl_bo_unpin (which does a reservation) without holding the
release_mutex lock.  Fixes lockdep (correctly) warning on a possible
deadlock.

Fixes: 65ffea3c6e73 ("drm/qxl: unpin release objects")
Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>

Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

---
  drivers/gpu/drm/qxl/qxl_release.c | 13 ++++++++++---
  1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c
index 716d706ca7f0..f5845c96d414 100644
--- a/drivers/gpu/drm/qxl/qxl_release.c
+++ b/drivers/gpu/drm/qxl/qxl_release.c
@@ -283,7 +283,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
  				       int type, struct qxl_release **release,
  				       struct qxl_bo **rbo)
  {
-	struct qxl_bo *bo;
+	struct qxl_bo *bo, *free_bo = NULL;
  	int idr_ret;
  	int ret = 0;
  	union qxl_release_info *info;
@@ -315,8 +315,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
mutex_lock(&qdev->release_mutex);
  	if (qdev->current_release_bo_offset[cur_idx] + 1 >= releases_per_bo[cur_idx]) {
-		qxl_bo_unpin(qdev->current_release_bo[cur_idx]);
-		qxl_bo_unref(&qdev->current_release_bo[cur_idx]);
+		free_bo = qdev->current_release_bo[cur_idx];
  		qdev->current_release_bo_offset[cur_idx] = 0;
  		qdev->current_release_bo[cur_idx] = NULL;
  	}
@@ -324,6 +323,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
  		ret = qxl_release_bo_alloc(qdev, &qdev->current_release_bo[cur_idx], priority);
  		if (ret) {
  			mutex_unlock(&qdev->release_mutex);
+			if (free_bo) {
+				qxl_bo_unpin(free_bo);
+				qxl_bo_unref(&free_bo);
+			}
  			qxl_release_free(qdev, *release);
  			return ret;
  		}
@@ -339,6 +342,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
  		*rbo = bo;
mutex_unlock(&qdev->release_mutex);
+	if (free_bo) {
+		qxl_bo_unpin(free_bo);
+		qxl_bo_unref(&free_bo);
+	}
ret = qxl_release_list_add(*release, bo);
  	qxl_bo_unref(&bo);


--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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