[PATCH 1/2] io_uring: drop mm and files after task_work_run

[Pavel Begunkov <asml.silence@gmail.com>]

__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.

Cc: stable@vger.kernel.org # 5.9+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2f305c097bd5..7af74c1ec909 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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();
-- 
2.24.0