[PATCH 7.2 15/82] io_uring/futex: only mark private futex waits as inflight

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@kernel.dk>

commit 4d327bbd1cd2485783553b6b2b401aa475f90dd0 upstream.

Inflight tracking of futex wait requests exists to ensure that do_exit()
-> io_uring_files_cancel() cancels them 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.

Shared futexes have no such dependency. A FLAGS_SHARED request always
resolves to either an inode based key or an mm-shared key, both of which
fail futex_key_is_private() and hence always hash into the global futex
hash, whose lifetime isn't tied to the mm.

Only mark vectored futex waits as inflight if the futex is private.

Cc: stable@vger.kernel.org
Fixes: 079afb081c42 ("io_uring/futex: mark wait requests as inflight")
Link: https://lore.kernel.org/io-uring/CANGjgdn=R_qyUdE=j9za+vkmqcxacbP-84OHXF4nZ4ho9qRyVg@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 io_uring/futex.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/io_uring/futex.c
+++ b/io_uring/futex.c
@@ -154,14 +154,16 @@ int io_futex_prep(struct io_kiocb *req,
 
 int io_futex_wait_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
+	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
 	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);
+	/* inflight tracking only needed for mm private hash */
+	if (!(iof->futex_flags & FLAGS_SHARED))
+		io_req_track_inflight(req);
 	return 0;
 }
 
@@ -186,6 +188,7 @@ int io_futexv_prep(struct io_kiocb *req,
 {
 	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
 	struct io_futexv_data *ifd;
+	unsigned int i;
 	int ret;
 
 	/* No flags or mask supported for waitv */
@@ -210,8 +213,14 @@ int io_futexv_prep(struct io_kiocb *req,
 		return ret;
 	}
 
-	/* Mark as inflight, so file exit cancelation will find it */
-	io_req_track_inflight(req);
+	/* inflight tracking only needed for mm private hash */
+	for (i = 0; i < iof->futex_nr; i++) {
+		if (!(ifd->futexv[i].w.flags & FLAGS_SHARED)) {
+			io_req_track_inflight(req);
+			break;
+		}
+	}
+
 	iof->futexv_unqueued = 0;
 	req->flags |= REQ_F_ASYNC_DATA;
 	req->async_data = ifd;