Patch "drm/amdkfd: Flush the process wq before creating a kfd_process" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    drm/amdkfd: Flush the process wq before creating a kfd_process

to the 6.8-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-amdkfd-flush-the-process-wq-before-creating-a-kf.patch
and it can be found in the queue-6.8 subdirectory.

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



commit e49ba0829046b79ce6aa8ee00de12212e33c9ef4
Author: Lancelot SIX <lancelot.six@xxxxxxx>
Date:   Wed Apr 10 14:14:13 2024 +0100

    drm/amdkfd: Flush the process wq before creating a kfd_process
    
    [ Upstream commit f5b9053398e70a0c10aa9cb4dd5910ab6bc457c5 ]
    
    There is a race condition when re-creating a kfd_process for a process.
    This has been observed when a process under the debugger executes
    exec(3).  In this scenario:
    - The process executes exec.
     - This will eventually release the process's mm, which will cause the
       kfd_process object associated with the process to be freed
       (kfd_process_free_notifier decrements the reference count to the
       kfd_process to 0).  This causes kfd_process_ref_release to enqueue
       kfd_process_wq_release to the kfd_process_wq.
    - The debugger receives the PTRACE_EVENT_EXEC notification, and tries to
      re-enable AMDGPU traps (KFD_IOC_DBG_TRAP_ENABLE).
     - When handling this request, KFD tries to re-create a kfd_process.
       This eventually calls kfd_create_process and kobject_init_and_add.
    
    At this point the call to kobject_init_and_add can fail because the
    old kfd_process.kobj has not been freed yet by kfd_process_wq_release.
    
    This patch proposes to avoid this race by making sure to drain
    kfd_process_wq before creating a new kfd_process object.  This way, we
    know that any cleanup task is done executing when we reach
    kobject_init_and_add.
    
    Signed-off-by: Lancelot SIX <lancelot.six@xxxxxxx>
    Reviewed-by: Felix Kuehling <felix.kuehling@xxxxxxx>
    Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index 58c1fe5421934..451bb058cc620 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -829,6 +829,14 @@ struct kfd_process *kfd_create_process(struct task_struct *thread)
 	if (process) {
 		pr_debug("Process already found\n");
 	} else {
+		/* If the process just called exec(3), it is possible that the
+		 * cleanup of the kfd_process (following the release of the mm
+		 * of the old process image) is still in the cleanup work queue.
+		 * Make sure to drain any job before trying to recreate any
+		 * resource for this process.
+		 */
+		flush_workqueue(kfd_process_wq);
+
 		process = create_process(thread);
 		if (IS_ERR(process))
 			goto out;