On Sat, May 23, 2026 at 01:53:15AM +0530, Harshit Mogalapalli wrote:

Hi Greg/Sasha,

On 20/05/26 21:54, Greg Kroah-Hartman wrote:

quoted

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

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

From: Paulo Alcantara <pc@manguebit.org>

commit 0aad5704c6b4d14007d4eab15883e8524e4310f4 upstream.

In netfs_extract_user_iter(), if iov_iter_extract_pages() failed to
extract user pages, bail out on -ENOMEM, otherwise return the error
code only if @npages == 0, allowing short DIO reads and writes to be
issued.

This fixes mmapstress02 from LTP tests against CIFS.

Fixes: 85dd2c8ff368 ("netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator")
Reported-by: Xiaoli Feng <redacted>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260512123404.719402-10-dhowells@redhat.com
Cc: netfs@lists.linux.dev
Cc: stable@vger.kernel.org
Cc: linux-cifs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
  fs/netfs/iterator.c |   13 ++++++++++---
  1 file changed, 10 insertions(+), 3 deletions(-)

--- a/fs/netfs/iterator.c
+++ b/fs/netfs/iterator.c

@@ -22,7 +22,7 @@
   *
   * Extract the page fragments from the given amount of the source iterator and
   * build up a second iterator that refers to all of those bits.  This allows
- * the original iterator to disposed of.
+ * the original iterator to be disposed of.
   *
   * @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA be
   * allowed on the pages extracted.

@@ -67,8 +67,8 @@ ssize_t netfs_extract_user_iter(struct i
  		ret = iov_iter_extract_pages(orig, &pages, count,
  					     max_pages - npages, extraction_flags,
  					     &offset);
-		if (ret < 0) {
-			pr_err("Couldn't get user pages (rc=%zd)\n", ret);
+		if (unlikely(ret <= 0)) {
+			ret = ret ?: -EIO;
  			break;
  		}

@@ -97,6 +97,13 @@ ssize_t netfs_extract_user_iter(struct i
  		npages += cur_npages;
  	}
+	if (ret < 0 && (ret == -ENOMEM || npages == 0)) {
+		for (i = 0; i < npages; i++)
+			unpin_user_page(bv[i].bv_page);
+		kvfree(bv);
+		return ret;
+	}
+

I have run an AI assisted backport review and it spotted an issue: I
have taken a look and the issues goes like:

Upstream has:



ssize_t ret = 0;

...
if (ret < 0 && (ret == -ENOMEM || npages == 0)) {
        for (i = 0; i < npages; i++)
                unpin_user_page(bv[i].bv_page);
        kvfree(bv);
        return ret;
}

6.12.y has:

ssize_t ret;

...
if (ret < 0 && (ret == -ENOMEM || npages == 0)) {
        for (i = 0; i < npages; i++)
                unpin_user_page(bv[i].bv_page);
        kvfree(bv);
        return ret;
}

I think 6.12.y misses commit: 7e3d8db899d5 ("netfs: Fix potential
uninitialised var in netfs_extract_user_iter()") so backport might not be
complete, thoughts ?

Now applied, thanks.

greg k-h