Patch "drm/msm: Fix hw_fence error path cleanup" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm/msm: Fix hw_fence error path cleanup

to the 6.4-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-msm-fix-hw_fence-error-path-cleanup.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit efb36738a671a194503abc80eeaf09607521be7c
Author: Rob Clark <robdclark@xxxxxxxxxxxx>
Date:   Wed Jul 12 15:25:23 2023 -0700

    drm/msm: Fix hw_fence error path cleanup
    
    [ Upstream commit 1cd0787f082e1a179f2b6e749d08daff1a9f6b1b ]
    
    In an error path where the submit is free'd without the job being run,
    the hw_fence pointer is simply a kzalloc'd block of memory.  In this
    case we should just kfree() it, rather than trying to decrement it's
    reference count.  Fortunately we can tell that this is the case by
    checking for a zero refcount, since if the job was run, the submit would
    be holding a reference to the hw_fence.
    
    Fixes: f94e6a51e17c ("drm/msm: Pre-allocate hw_fence")
    Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
    Patchwork: https://patchwork.freedesktop.org/patch/547088/
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c
index 96599ec3eb783..1a5d4f1c8b422 100644
--- a/drivers/gpu/drm/msm/msm_fence.c
+++ b/drivers/gpu/drm/msm/msm_fence.c
@@ -191,6 +191,12 @@ msm_fence_init(struct dma_fence *fence, struct msm_fence_context *fctx)
 
 	f->fctx = fctx;
 
+	/*
+	 * Until this point, the fence was just some pre-allocated memory,
+	 * no-one should have taken a reference to it yet.
+	 */
+	WARN_ON(kref_read(&fence->refcount));
+
 	dma_fence_init(&f->base, &msm_fence_ops, &fctx->spinlock,
 		       fctx->context, ++fctx->last_fence);
 }
diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index 9f5933c75e3df..10cad7b99bac8 100644
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -86,7 +86,19 @@ void __msm_gem_submit_destroy(struct kref *kref)
 	}
 
 	dma_fence_put(submit->user_fence);
-	dma_fence_put(submit->hw_fence);
+
+	/*
+	 * If the submit is freed before msm_job_run(), then hw_fence is
+	 * just some pre-allocated memory, not a reference counted fence.
+	 * Once the job runs and the hw_fence is initialized, it will
+	 * have a refcount of at least one, since the submit holds a ref
+	 * to the hw_fence.
+	 */
+	if (kref_read(&submit->hw_fence->refcount) == 0) {
+		kfree(submit->hw_fence);
+	} else {
+		dma_fence_put(submit->hw_fence);
+	}
 
 	put_pid(submit->pid);
 	msm_submitqueue_put(submit->queue);