FAILED: patch "[PATCH] io_uring/kbuf: support min length left for incremental" failed to apply to 6.18-stable tree

FAILED: patch "[PATCH] io_uring/kbuf: support min length left for incremental" failed to apply to 6.18-stable tree

[gregkh]

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 7deba791ad495ce1d7921683f4f7d1190fa210d1
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051232-kindred-spooky-37ac@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7deba791ad495ce1d7921683f4f7d1190fa210d1 Mon Sep 17 00:00:00 2001
From: Martin Michaelis <code@mgjm.de>
Date: Thu, 23 Apr 2026 15:54:11 -0600
Subject: [PATCH] io_uring/kbuf: support min length left for incremental
 buffers

Incrementally consumed buffer rings are generally fully consumed, but
it's quite possible that the application has a minimum size it needs to
meet to avoid truncation. Currently that minimum limit is 1 byte, but
this should be a setting that is the hands of the application. For
recvmsg multishot, a prime use case for incrementally consumed buffers,
the application may get spurious -EFAULT returned at the end of an
incrementally consumed buffer, as less space is available than the
headers need.

Grab a u32 field in struct io_uring_buf_reg, which the application can
use to inform the kernel of the minimum size that should be available
in an incrementally consumed buffer. If less than that is available,
the current buffer is fully processed and the next one will be picked.

Cc: stable@vger.kernel.org
Fixes: ae98dbf43d75 ("io_uring/kbuf: add support for incremental buffer consumption")
Link: https://github.com/axboe/liburing/issues/1433
Signed-off-by: Martin Michaelis <code@mgjm.de>
[axboe: write commit message, change io_buffer_list member name]
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 17ac1b785440..909fb7aea638 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -905,7 +905,8 @@ struct io_uring_buf_reg {
 	__u32	ring_entries;
 	__u16	bgid;
 	__u16	flags;
-	__u64	resv[3];
+	__u32	min_left;
+	__u32	resv[5];
 };
 
 /* argument for IORING_REGISTER_PBUF_STATUS */
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 43e4f8615fe8..63061aa1cab9 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -47,7 +47,7 @@ static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 		this_len = min_t(u32, len, buf_len);
 		buf_len -= this_len;
 		/* Stop looping for invalid buffer length of 0 */
-		if (buf_len || !this_len) {
+		if (buf_len > bl->min_left_sub_one || !this_len) {
 			WRITE_ONCE(buf->addr, READ_ONCE(buf->addr) + this_len);
 			WRITE_ONCE(buf->len, buf_len);
 			return false;
@@ -637,6 +637,10 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 	if (reg.ring_entries >= 65536)
 		return -EINVAL;
 
+	/* minimum left byte count is a property of incremental buffers */
+	if (!(reg.flags & IOU_PBUF_RING_INC) && reg.min_left)
+		return -EINVAL;
+
 	bl = io_buffer_get_list(ctx, reg.bgid);
 	if (bl) {
 		/* if mapped buffer ring OR classic exists, don't allow */
@@ -683,6 +687,8 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 	bl->mask = reg.ring_entries - 1;
 	bl->flags |= IOBL_BUF_RING;
 	bl->buf_ring = br;
+	if (reg.min_left)
+		bl->min_left_sub_one = reg.min_left - 1;
 	if (reg.flags & IOU_PBUF_RING_INC)
 		bl->flags |= IOBL_INC;
 	ret = io_buffer_add_list(ctx, bl, reg.bgid);
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index abf7052b556e..401773e1ef80 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -32,6 +32,13 @@ struct io_buffer_list {
 
 	__u16 flags;
 
+	/*
+	 * minimum required amount to be left to reuse an incrementally
+	 * consumed buffer. If less than this is left at consumption time,
+	 * buffer is done and head is incremented to the next buffer.
+	 */
+	__u32 min_left_sub_one;
+
 	struct io_mapped_region region;
 };
 

Re: FAILED: patch "[PATCH] io_uring/kbuf: support min length left for incremental" failed to apply to 6.18-stable tree

[Jens Axboe]

[-- Attachment #1: Type: text/plain, Size: 805 bytes --]

On 5/12/26 6:41 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.18-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-6.18.y
> git checkout FETCH_HEAD
> git cherry-pick -x 7deba791ad495ce1d7921683f4f7d1190fa210d1
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051232-kindred-spooky-37ac@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Here's one for 6.18-stable.

-- 
Jens Axboe

[-- Attachment #2: 0002-io_uring-kbuf-support-min-length-left-for-incrementa.patch --]
[-- Type: text/x-patch, Size: 3893 bytes --]

From ae165fed72f9686aeb04766a15459807114a5023 Mon Sep 17 00:00:00 2001
From: Martin Michaelis <code@mgjm.de>
Date: Thu, 23 Apr 2026 15:54:11 -0600
Subject: [PATCH 2/2] io_uring/kbuf: support min length left for incremental
 buffers

Commit 7deba791ad495ce1d7921683f4f7d1190fa210d1 upstream.

Incrementally consumed buffer rings are generally fully consumed, but
it's quite possible that the application has a minimum size it needs to
meet to avoid truncation. Currently that minimum limit is 1 byte, but
this should be a setting that is the hands of the application. For
recvmsg multishot, a prime use case for incrementally consumed buffers,
the application may get spurious -EFAULT returned at the end of an
incrementally consumed buffer, as less space is available than the
headers need.

Grab a u32 field in struct io_uring_buf_reg, which the application can
use to inform the kernel of the minimum size that should be available
in an incrementally consumed buffer. If less than that is available,
the current buffer is fully processed and the next one will be picked.

Cc: stable@vger.kernel.org
Fixes: ae98dbf43d75 ("io_uring/kbuf: add support for incremental buffer consumption")
Link: https://github.com/axboe/liburing/issues/1433
Signed-off-by: Martin Michaelis <code@mgjm.de>
[axboe: write commit message, change io_buffer_list member name]
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/uapi/linux/io_uring.h |  3 ++-
 io_uring/kbuf.c               | 12 +++++++++---
 io_uring/kbuf.h               |  7 +++++++
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index b7c8dad26690..ef5b734b5a41 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -864,7 +864,8 @@ struct io_uring_buf_reg {
 	__u32	ring_entries;
 	__u16	bgid;
 	__u16	flags;
-	__u64	resv[3];
+	__u32	min_left;
+	__u32	resv[5];
 };
 
 /* argument for IORING_REGISTER_PBUF_STATUS */
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 9e8166e24dc8..32d3b8d26bf0 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -47,9 +47,9 @@ static bool io_kbuf_inc_commit(struct io_buffer_list *bl, int len)
 		this_len = min_t(u32, len, buf_len);
 		buf_len -= this_len;
 		/* Stop looping for invalid buffer length of 0 */
-		if (buf_len || !this_len) {
-			buf->addr = READ_ONCE(buf->addr) + this_len;
-			buf->len = buf_len;
+		if (buf_len > bl->min_left_sub_one || !this_len) {
+			WRITE_ONCE(buf->addr, READ_ONCE(buf->addr) + this_len);
+			WRITE_ONCE(buf->len, buf_len);
 			return false;
 		}
 		buf->len = 0;
@@ -637,6 +637,10 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 	if (reg.ring_entries >= 65536)
 		return -EINVAL;
 
+	/* minimum left byte count is a property of incremental buffers */
+	if (!(reg.flags & IOU_PBUF_RING_INC) && reg.min_left)
+		return -EINVAL;
+
 	bl = io_buffer_get_list(ctx, reg.bgid);
 	if (bl) {
 		/* if mapped buffer ring OR classic exists, don't allow */
@@ -684,6 +688,8 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
 	bl->mask = reg.ring_entries - 1;
 	bl->flags |= IOBL_BUF_RING;
 	bl->buf_ring = br;
+	if (reg.min_left)
+		bl->min_left_sub_one = reg.min_left - 1;
 	if (reg.flags & IOU_PBUF_RING_INC)
 		bl->flags |= IOBL_INC;
 	ret = io_buffer_add_list(ctx, bl, reg.bgid);
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index ada382ff38d7..d1d00e040dfe 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -34,6 +34,13 @@ struct io_buffer_list {
 
 	__u16 flags;
 
+	/*
+	 * minimum required amount to be left to reuse an incrementally
+	 * consumed buffer. If less than this is left at consumption time,
+	 * buffer is done and head is incremented to the next buffer.
+	 */
+	__u32 min_left_sub_one;
+
 	struct io_mapped_region region;
 };
 
-- 
2.53.0

Re: FAILED: patch "[PATCH] io_uring/kbuf: support min length left for incremental" failed to apply to 6.18-stable tree

[Greg KH]

On Tue, May 12, 2026 at 07:48:12AM -0600, Jens Axboe wrote:
> On 5/12/26 6:41 AM, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 6.18-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-6.18.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x 7deba791ad495ce1d7921683f4f7d1190fa210d1
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026051232-kindred-spooky-37ac@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..
> 
> Here's one for 6.18-stable.

Both n ow applied, thanks.

greg k-h