Re: FAILED: patch "[PATCH] io_uring/kbuf: flag partial buffer mappings" failed to apply to 6.15-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 6/29/25 6:42 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.15.y
> git checkout FETCH_HEAD
> git cherry-pick -x 178b8ff66ff827c41b4fa105e9aabb99a0b5c537
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025062920-conch-hypnotist-d63d@gregkh' --subject-prefix 'PATCH 6.15.y' HEAD^..

Easiest with a backport of another fix done on top, even if it isn't
necessary for 6.15-stable.

-- 
Jens Axboe

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From d0077a0341132e979b542cc5571938e89071c953 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 26 Jun 2025 12:17:48 -0600
Subject: [PATCH 2/2] io_uring/kbuf: flag partial buffer mappings

Commit 178b8ff66ff827c41b4fa105e9aabb99a0b5c537 upstream.

A previous commit aborted mapping more for a non-incremental ring for
bundle peeking, but depending on where in the process this peeking
happened, it would not necessarily prevent a retry by the user. That can
create gaps in the received/read data.

Add struct buf_sel_arg->partial_map, which can pass this information
back. The networking side can then map that to internal state and use it
to gate retry as well.

Since this necessitates a new flag, change io_sr_msg->retry to a
retry_flags member, and store both the retry and partial map condition
in there.

Cc: stable@vger.kernel.org
Fixes: 26ec15e4b0c1 ("io_uring/kbuf: don't truncate end buffer for multiple buffer peeks")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/kbuf.c |  1 +
 io_uring/kbuf.h |  1 +
 io_uring/net.c  | 23 +++++++++++++++--------
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index a8467f6aba54..6c676aedc9a2 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -271,6 +271,7 @@ static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
 		if (len > arg->max_len) {
 			len = arg->max_len;
 			if (!(bl->flags & IOBL_INC)) {
+				arg->partial_map = 1;
 				if (iov != arg->iovs)
 					break;
 				buf->len = len;
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index 2ec0b983ce24..6eb16ba6ed39 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -55,6 +55,7 @@ struct buf_sel_arg {
 	size_t max_len;
 	unsigned short nr_iovs;
 	unsigned short mode;
+	unsigned short partial_map;
 };
 
 void __user *io_buffer_select(struct io_kiocb *req, size_t *len,
diff --git a/io_uring/net.c b/io_uring/net.c
index adfdcea01e39..7bf5e62d5a29 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -76,12 +76,17 @@ struct io_sr_msg {
 	u16				flags;
 	/* initialised and used only by !msg send variants */
 	u16				buf_group;
-	bool				retry;
+	unsigned short			retry_flags;
 	void __user			*msg_control;
 	/* used only for send zerocopy */
 	struct io_kiocb 		*notif;
 };
 
+enum sr_retry_flags {
+	IO_SR_MSG_RETRY		= 1,
+	IO_SR_MSG_PARTIAL_MAP	= 2,
+};
+
 /*
  * 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
@@ -188,7 +193,7 @@ static inline void io_mshot_prep_retry(struct io_kiocb *req,
 
 	req->flags &= ~REQ_F_BL_EMPTY;
 	sr->done_io = 0;
-	sr->retry = false;
+	sr->retry_flags = 0;
 	sr->len = 0; /* get from the provided buffer */
 	req->buf_index = sr->buf_group;
 }
@@ -401,7 +406,7 @@ int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 
 	sr->done_io = 0;
-	sr->retry = false;
+	sr->retry_flags = 0;
 	sr->len = READ_ONCE(sqe->len);
 	sr->flags = READ_ONCE(sqe->ioprio);
 	if (sr->flags & ~SENDMSG_FLAGS)
@@ -759,7 +764,7 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 
 	sr->done_io = 0;
-	sr->retry = false;
+	sr->retry_flags = 0;
 
 	if (unlikely(sqe->file_index || sqe->addr2))
 		return -EINVAL;
@@ -831,7 +836,7 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
 
 		cflags |= io_put_kbufs(req, this_ret, io_bundle_nbufs(kmsg, this_ret),
 				      issue_flags);
-		if (sr->retry)
+		if (sr->retry_flags & IO_SR_MSG_RETRY)
 			cflags = req->cqe.flags | (cflags & CQE_F_MASK);
 		/* bundle with no more immediate buffers, we're done */
 		if (req->flags & REQ_F_BL_EMPTY)
@@ -840,12 +845,12 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
 		 * If more is available AND it was a full transfer, retry and
 		 * append to this one
 		 */
-		if (!sr->retry && kmsg->msg.msg_inq > 1 && this_ret > 0 &&
+		if (!sr->retry_flags && kmsg->msg.msg_inq > 1 && this_ret > 0 &&
 		    !iov_iter_count(&kmsg->msg.msg_iter)) {
 			req->cqe.flags = cflags & ~CQE_F_MASK;
 			sr->len = kmsg->msg.msg_inq;
 			sr->done_io += this_ret;
-			sr->retry = true;
+			sr->retry_flags |= IO_SR_MSG_RETRY;
 			return false;
 		}
 	} else {
@@ -1089,6 +1094,8 @@ static int io_recv_buf_select(struct io_kiocb *req, struct io_async_msghdr *kmsg
 			kmsg->vec.iovec = arg.iovs;
 			req->flags |= REQ_F_NEED_CLEANUP;
 		}
+		if (arg.partial_map)
+			sr->retry_flags |= IO_SR_MSG_PARTIAL_MAP;
 
 		/* special case 1 vec, can be a fast path */
 		if (ret == 1) {
@@ -1285,7 +1292,7 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	int ret;
 
 	zc->done_io = 0;
-	zc->retry = false;
+	zc->retry_flags = 0;
 
 	if (unlikely(READ_ONCE(sqe->__pad2[0]) || READ_ONCE(sqe->addr3)))
 		return -EINVAL;
-- 
2.50.0


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From ceb63266aa67986bceec223109dc3984e3bef706 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 25 Jun 2025 10:17:06 -0600
Subject: [PATCH 1/2] io_uring/net: mark iov as dynamically allocated even for
 single segments

Commit 9a709b7e98e6fa51600b5f2d24c5068efa6d39de upstream.

A bigger array of vecs could've been allocated, but
io_ring_buffers_peek() still decided to cap the mapped range depending
on how much data was available. Hence don't rely on the segment count
to know if the request should be marked as needing cleanup, always
check upfront if the iov array is different than the fast_iov array.

Fixes: 26ec15e4b0c1 ("io_uring/kbuf: don't truncate end buffer for multiple buffer peeks")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/net.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index 3feceb2b5b97..adfdcea01e39 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -1084,6 +1084,12 @@ static int io_recv_buf_select(struct io_kiocb *req, struct io_async_msghdr *kmsg
 		if (unlikely(ret < 0))
 			return ret;
 
+		if (arg.iovs != &kmsg->fast_iov && arg.iovs != kmsg->vec.iovec) {
+			kmsg->vec.nr = ret;
+			kmsg->vec.iovec = arg.iovs;
+			req->flags |= REQ_F_NEED_CLEANUP;
+		}
+
 		/* special case 1 vec, can be a fast path */
 		if (ret == 1) {
 			sr->buf = arg.iovs[0].iov_base;
@@ -1092,11 +1098,6 @@ static int io_recv_buf_select(struct io_kiocb *req, struct io_async_msghdr *kmsg
 		}
 		iov_iter_init(&kmsg->msg.msg_iter, ITER_DEST, arg.iovs, ret,
 				arg.out_len);
-		if (arg.iovs != &kmsg->fast_iov && arg.iovs != kmsg->vec.iovec) {
-			kmsg->vec.nr = ret;
-			kmsg->vec.iovec = arg.iovs;
-			req->flags |= REQ_F_NEED_CLEANUP;
-		}
 	} else {
 		void __user *buf;
 
-- 
2.50.0