[PATCH AUTOSEL 5.15 12/15] drm/amdkfd: Flush the process wq before creating a kfd_process

Sasha Levin
2024-05-07T23:13:56Z

From: Lancelot SIX <lancelot.six@amd.com>

[ 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@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/amd/amdkfd/kfd_process.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index 21ec8a18cad29..7f69031f2b61a 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -818,6 +818,14 @@ struct kfd_process *kfd_create_process(struct file *filep)
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;
--
2.43.0