Re: [PATCH 6.6.y] smb: client: support kvec iterators in async read path

[Bharath SM <bharathsm.hsk@gmail.com>]

On Thu, Nov 27, 2025 at 5:30 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Fri, Nov 21, 2025 at 02:31:20AM -0800, Bharath SM wrote:
> > On Fri, Nov 21, 2025 at 2:02 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Thu, Nov 06, 2025 at 06:02:39AM -0800, Bharath SM wrote:
> > > > On Fri, Jul 11, 2025 at 9:01 AM Henrique Carvalho
> > > > <henrique.carvalho@suse.com> wrote:
> > > > >
> > > > > On Fri, Jul 11, 2025 at 10:01:58AM +0100, David Howells wrote:
> > > > > > Henrique Carvalho <henrique.carvalho@suse.com> wrote:
> > > > > >
> > > > > > > Add cifs_limit_kvec_subset() and select the appropriate limiter in
> > > > > > > cifs_send_async_read() to handle kvec iterators in async read path,
> > > > > > > fixing the EIO bug when running executables in cifs shares mounted
> > > > > > > with nolease.
> > > > > > >
> > > > > > > This patch -- or equivalent patch, does not exist upstream, as the
> > > > > > > upstream code has suffered considerable API changes. The affected path
> > > > > > > is currently handled by netfs lib and located under netfs/direct_read.c.
> > > > > >
> > > > > > Are you saying that you do see this upstream too?
> > > > > >
> > > > >
> > > > > No, the patch only targets the 6.6.y stable tree. Since version 6.8,
> > > > > this path has moved into the netfs layer, so the original bug no longer
> > > > > exists.
> > > > >
> > > > > The bug was fixed at least since the commit referred in the commit
> > > > > message -- 3ee1a1fc3981. In this commit, the call to cifs_user_readv()
> > > > > is replaced by a call to netfs_unbuffered_read_iter(), inside the
> > > > > function cifs_strict_readv().
> > > > >
> > > > > netfs_unbuffered_read_iter() itself was introduced in commit
> > > > > 016dc8516aec8, along with other netfs api changes, present in kernel
> > > > > versions 6.8+.
> > > > >
> > > > > Backporting netfs directly would be non-trivial. Instead, I:
> > > > >
> > > > > - add cifs_limit_kvec_subset(), modeled on the existing
> > > > >   cifs_limit_bvec_subset()
> > > > > - choose between the kvec or bvec limiter function early in
> > > > >   cifs_write_from_iter().
> > > > >
> > > > > The Fixes tag references d08089f649a0c, which implements
> > > > > cifs_limit_bvec_subset() and uses it inside cifs_write_from_iter().
> > > > >
> > > > > > > Reproducer:
> > > > > > >
> > > > > > > $ mount.cifs //server/share /mnt -o nolease
> > > > > > > $ cat - > /mnt/test.sh <<EOL
> > > > > > > echo hallo
> > > > > > > EOL
> > > > > > > $ chmod +x /mnt/test.sh
> > > > > > > $ /mnt/test.sh
> > > > > > > bash: /mnt/test.sh: /bin/bash: Defekter Interpreter: Eingabe-/Ausgabefehler
> > > > > > > $ rm -f /mnt/test.sh
> > > > > >
> > > > > > Is this what you are expecting to see when it works or when it fails?
> > > > > >
> > > > >
> > > > > This is the reproducer for the observed bug. In english it reads "Bad
> > > > > interpreter: Input/Output error".
> > > > >
> > > > > FYI: I tried to follow Option 3 of the stable-kernel rules for submission:
> > > > > <https://www.kernel.org/doc/html/v6.15/process/stable-kernel-rules.html>
> > > > > Please let me know if you'd prefer a different approach or any further
> > > > > changes.
> > > > Thanks Henrique.
> > > >
> > > > Hi Greg,
> > > >
> > > > We are observing the same issue with the 6.6 Kernel, Can you please
> > > > help include this patch in the 6.6 stable kernel.?
> > >
> > > Pleas provide a working backport and we will be glad to imclude it.
> > >
> > This fix is not needed now in the stable kernels as "[PATCH] cifs: Fix
> > uncached read into ITER_KVEC iterator" submitted
> > in email thread "Request to backport data corruption fix to stable"
> > fixes this issue.
>
> I do not understand, what commit fixed this?  You attached a fix, but
> that's not needed?

For the issue described originally in this thread, both David and
Henrique has submitted different fixes.
Since David's patch already merged to stable kernel 6.6 recently, we
don't need the patch submitted by Henriqie in this thread.

Link to david's patch that is already in 6.6 stable:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/fs/smb/client?h=linux-6.6.y&id=25d6e76639323ee3d1fb4df7066c6d79190f6c33

Thank you.!