FAILED: patch "[PATCH] io_uring: drop mm and files after task_work_run" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d434ab6db524ab1efd0afad4ffa1ee65ca6ac097 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <[email protected]>
Date: Mon, 11 Jan 2021 04:00:30 +0000
Subject: [PATCH] io_uring: drop mm and files after task_work_run

__io_req_task_submit() run by task_work can set mm and files, but io_sq_thread() in some cases, and because __io_sq_thread_acquire_mm() and __io_sq_thread_acquire_files() do a simple current->mm/files check it may end up submitting IO with mm/files of another task.

We also need to drop it after in the end to drop potentially grabbed references to them.

index 2f305c097bd5..7af74c1ec909 100644
@@ -7056,6 +7056,7 @@ static int io_sq_thread(void *data)
 
 		if (sqt_spin || !time_after(jiffies, timeout)) {
 			io_run_task_work();
+			io_sq_thread_drop_mm_files();
 			cond_resched();
 			if (sqt_spin)
 				timeout = jiffies + sqd->sq_thread_idle;

@@ -7093,6 +7094,7 @@ static int io_sq_thread(void *data)
 	}
 
 	io_run_task_work();
+	io_sq_thread_drop_mm_files();
 
 	if (cur_css)
 		io_sq_thread_unassociate_blkcg();