This is a note to let you know that I've just added the patch titled
io_uring/net: limit inline multishot retries
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-net-limit-inline-multishot-retries.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From aeec8884c1607a73b379e610cc8de27e3f6244ce Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Mon, 29 Jan 2024 12:00:58 -0700
Subject: io_uring/net: limit inline multishot retries
From: Jens Axboe <axboe@xxxxxxxxx>
Commit 76b367a2d83163cf19173d5cb0b562acbabc8eac upstream.
If we have multiple clients and some/all are flooding the receives to
such an extent that we can retry a LOT handling multishot receives, then
we can be starving some clients and hence serving traffic in an
imbalanced fashion.
Limit multishot retry attempts to some arbitrary value, whose only
purpose serves to ensure that we don't keep serving a single connection
for way too long. We default to 32 retries, which should be more than
enough to provide fairness, yet not so small that we'll spend too much
time requeuing rather than handling traffic.
Cc: stable@xxxxxxxxxxxxxxx
Depends-on: 704ea888d646 ("io_uring/poll: add requeue return code from poll multishot handling")
Depends-on: 1e5d765a82f ("io_uring/net: un-indent mshot retry path in io_recv_finish()")
Depends-on: e84b01a880f6 ("io_uring/poll: move poll execution helpers higher up")
Fixes: b3fdea6ecb55 ("io_uring: multishot recv")
Fixes: 9bb66906f23e ("io_uring: support multishot in recvmsg")
Link: https://github.com/axboe/liburing/issues/1043
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
io_uring/net.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -60,6 +60,7 @@ struct io_sr_msg {
unsigned len;
unsigned done_io;
unsigned msg_flags;
+ unsigned nr_multishot_loops;
u16 flags;
/* initialised and used only by !msg send variants */
u16 addr_len;
@@ -70,6 +71,13 @@ struct io_sr_msg {
struct io_kiocb *notif;
};
+/*
+ * Number of times we'll try and do receives if there's more data. If we
+ * exceed this limit, then add us to the back of the queue and retry from
+ * there. This helps fairness between flooding clients.
+ */
+#define MULTISHOT_MAX_RETRY 32
+
static inline bool io_check_multishot(struct io_kiocb *req,
unsigned int issue_flags)
{
@@ -611,6 +619,7 @@ int io_recvmsg_prep(struct io_kiocb *req
sr->msg_flags |= MSG_CMSG_COMPAT;
#endif
sr->done_io = 0;
+ sr->nr_multishot_loops = 0;
return 0;
}
@@ -654,12 +663,20 @@ static inline bool io_recv_finish(struct
*/
if (io_fill_cqe_req_aux(req, issue_flags & IO_URING_F_COMPLETE_DEFER,
*ret, cflags | IORING_CQE_F_MORE)) {
+ struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
+ int mshot_retry_ret = IOU_ISSUE_SKIP_COMPLETE;
+
io_recv_prep_retry(req);
/* Known not-empty or unknown state, retry */
- if (cflags & IORING_CQE_F_SOCK_NONEMPTY || msg->msg_inq == -1)
- return false;
+ if (cflags & IORING_CQE_F_SOCK_NONEMPTY || msg->msg_inq == -1) {
+ if (sr->nr_multishot_loops++ < MULTISHOT_MAX_RETRY)
+ return false;
+ /* mshot retries exceeded, force a requeue */
+ sr->nr_multishot_loops = 0;
+ mshot_retry_ret = IOU_REQUEUE;
+ }
if (issue_flags & IO_URING_F_MULTISHOT)
- *ret = IOU_ISSUE_SKIP_COMPLETE;
+ *ret = mshot_retry_ret;
else
*ret = -EAGAIN;
return true;
Patches currently in stable-queue which might be from axboe@xxxxxxxxx are
queue-6.6/io_uring-poll-add-requeue-return-code-from-poll-multishot-handling.patch
queue-6.6/io_uring-net-limit-inline-multishot-retries.patch
queue-6.6/blk-iocost-fix-an-ubsan-shift-out-of-bounds-warning.patch
queue-6.6/io_uring-net-fix-sr-len-for-ioring_op_recv-with-msg_waitall-and-buffers.patch
queue-6.6/io_uring-net-un-indent-mshot-retry-path-in-io_recv_finish.patch
queue-6.6/io_uring-poll-move-poll-execution-helpers-higher-up.patch
