netfs: fix error handling in netfs_extract_user_iter()

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>
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>

diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index 6903028b71620c811fffb463970dc5d190731803..429e4396e1b00000abc5f8cd32be39178ecf7541 100644 (file)
--- 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;
 }