From f5b9053398e70a0c10aa9cb4dd5910ab6bc457c5 Mon Sep 17 00:00:00 2001 From: Lancelot SIX Date: Wed, 10 Apr 2024 14:14:13 +0100 Subject: drm/amdkfd: Flush the process wq before creating a kfd_process 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 Reviewed-by: Felix Kuehling Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/amdkfd/kfd_process.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'drivers') diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c index 58c1fe542193..451bb058cc62 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; -- cgit v1.2.3