io_uring/futex: don't mark futex wake requests as inflight

Commit 079afb081c ("io_uring/futex: mark wait requests as inflight")
added inflight tracking to ensure that do_exit() ->
io_uring_files_cancel() finds and cancels pending futex waits before the
mm goes away, as a private futex wait depends on the mm private futex
hash staying alive for the duration of the request. However, as
io_futex_prep() is shared between FUTEX_WAIT and FUTEX_WAKE, wake
requests got marked as inflight as well.

A futex wake executes fully inline at issue time and never depends on
the mm staying alive after completion, hence there's no need to track
it. Kill it.

Cc: stable@vger.kernel.org
Fixes: 079afb081c ("io_uring/futex: mark wait requests as inflight")
Reported-by: Chengfeng Lin <lin2530632123@gmail.com>
Link: https://lore.kernel.org/io-uring/CANGjgdn=R_qyUdE=j9za+vkmqcxacbP-84OHXF4nZ4ho9qRyVg@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/futex.c

@@ -149,6 +149,17 @@ int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	    !futex_validate_input(iof->futex_flags, iof->futex_mask))
 		return -EINVAL;
 
+	return 0;
+}
+
+int io_futex_wait_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	int ret;
+
+	ret = io_futex_prep(req, sqe);
+	if (unlikely(ret))
+		return ret;
+
 	/* Mark as inflight, so file exit cancelation will find it */
 	io_req_track_inflight(req);
 	return 0;

io_uring/futex.h

@@ -3,6 +3,7 @@
 #include "cancel.h"
 
 int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_futex_wait_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_futexv_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_futex_wait(struct io_kiocb *req, unsigned int issue_flags);
 int io_futexv_wait(struct io_kiocb *req, unsigned int issue_flags);

io_uring/opdef.c

@@ -467,7 +467,7 @@ const struct io_issue_def io_issue_defs[] = {
 	},
 	[IORING_OP_FUTEX_WAIT] = {
 #if defined(CONFIG_FUTEX)
-		.prep			= io_futex_prep,
+		.prep			= io_futex_wait_prep,
 		.issue			= io_futex_wait,
 #else
 		.prep			= io_eopnotsupp_prep,