[PATCH v2 2/7] netfs: fix error handling in netfs_extract_user_iter()

David Howells
2026-04-14T08:20:25Z

From: Paulo Alcantara <pc@manguebit.org>

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 <xifeng@redhat.com>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: David Howells <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
---
fs/netfs/iterator.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index 154a14bb2d7f..adca78747f23 100644
--- 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 iov_iter *orig, size_t orig_len,
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 iov_iter *orig, size_t orig_len,
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;
+ }
+
iov_iter_bvec(new, orig->data_source, bv, npages, orig_len - count);
return npages;
}