Re: [PATCH 6.12 634/666] netfs: fix error handling in netfs_extract_user_iter()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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:
> > 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 <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>
> > 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