On 5/28/26 10:29, w15303746062@163.com wrote:

From: Mingyu Wang 25181214217@stu.xidian.edu.cn

Syzkaller fuzzer triggered a kernel panic via a WARNING in drm_prime_destroy_file_private() due to a non-empty prime rb_tree.

The root cause is a complete lack of synchronization in the teardown path. While the import path (drm_gem_prime_fd_to_handle) holds the &file_priv->prime.lock during lookup and insertion, the deletion path (drm_prime_remove_buf_handle) traverses and mutates both the 'handles' and 'dmabufs' rb_trees without acquiring any mutex.

That's just simply incorrect, drm_prime_remove_buf_handle() is called with the lock already held.

See drm_gem_object_release_handle():

mutex_lock(&file_priv->prime.lock);

drm_prime_remove_buf_handle(&file_priv->prime, id);

mutex_unlock(&file_priv->prime.lock);

So the patch you propose here is just nonsense.

What tree are you working on? Could it be that this is something specific to a certain version.

Regards, Christian.

When multiple threads concurrently close GEM handles or interleave import and close operations, the pointers and balance states of the rb_tree nodes get corrupted. As a result, certain members are erased from one tree but remain orphaned in the other. Upon process exit, the final sanity check triggers the WARNING.

[ 448.919314][T19739] ------------[ cut here ]------------ [ 448.945387][T19739] WARNING: CPU: 0 PID: 19739 at drivers/gpu/drm/drm_prime.c:223 drm_prime_destroy_file_private+0x43/0x60 ... [ 449.056535][T19739] Call Trace: [ 449.056544][T19739] <TASK> [ 449.056553][T19739] drm_file_free.part.0+0x805/0xcf0 [ 449.056652][T19739] drm_close_helper.isra.0+0x183/0x1f0 [ 449.056677][T19739] drm_release+0x1ab/0x360 [ 449.056719][T19739] __fput+0x402/0xb50 [ 449.056783][T19739] task_work_run+0x16b/0x260 [ 449.056883][T19739] exit_to_user_mode_loop+0xf9/0x130 [ 449.056931][T19739] do_syscall_64+0x424/0xfa0 [ 449.056977][T19739] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 449.057268][T19739] </TASK> [ 449.057295][T19739] Kernel panic - not syncing: kernel: panic_on_warn set ...

Fix this by acquiring the prime_fpriv->lock mutex around the rb_tree lookup and erasure logic. To respect the locking rules and avoid potential deadlocks with driver-specific memory cleanups, assign the target node to a temporary pointer and defer the dma_buf_put() and kfree() operations until after the mutex is safely dropped.

Fixes: ea2aa97ca37a ("drm/gem: Fix GEM handle release errors") Cc: stable@vger.kernel.org Signed-off-by: Mingyu Wang 25181214217@stu.xidian.edu.cn

---

drivers/gpu/drm/drm_prime.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 9b44c78cd77f..26319c638e0f 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -190,6 +190,9 @@ void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, uint32_t handle) { struct rb_node *rb;

•   struct drm_prime_member *found = NULL;
  

•   mutex_lock(&prime_fpriv->lock);
  
    rb = prime_fpriv->handles.rb_node;
    while (rb) {
  

@@ -200,8 +203,7 @@ void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, rb_erase(&member->handle_rb, &prime_fpriv->handles); rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);

•                   dma_buf_put(member->dma_buf);
  

•                   kfree(member);
  

•                   found = member;
                    break;
            } else if (member->handle < handle) {
                    rb = rb->rb_right;
  

@@ -209,6 +211,13 @@ void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, rb = rb->rb_left; } }

•   mutex_unlock(&prime_fpriv->lock);
  

•   /* Defer resource release outside the mutex to prevent deadlocks */
  

•   if (found) {
  

•           dma_buf_put(found->dma_buf);
  

•           kfree(found);
  

•   }
  

}

void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)

2.34.1