io_uring: don't take files/mm for a dead task

In rare cases a task may be exiting while io_ring_exit_work() trying to
cancel/wait its requests. It's ok for __io_sq_thread_acquire_mm()
because of SQPOLL check, but is not for __io_sq_thread_acquire_files().
Play safe and fail for both of them.

Cc: stable@vger.kernel.org # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7af74c1ec9091b2307d97c27bc8f35326b338c16..b0e6d8e607a33982ba108cbcd0bc55358290ca51 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1106,6 +1106,9 @@ static void io_sq_thread_drop_mm_files(void)
 
 static int __io_sq_thread_acquire_files(struct io_ring_ctx *ctx)
 {
+       if (current->flags & PF_EXITING)
+               return -EFAULT;
+
        if (!current->files) {
                struct files_struct *files;
                struct nsproxy *nsproxy;
@@ -1133,6 +1136,8 @@ static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
 {
        struct mm_struct *mm;
 
+       if (current->flags & PF_EXITING)
+               return -EFAULT;
        if (current->mm)
                return 0;