Re: [PATCH] cifs: Always resolve hostname before reconnecting

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Feb 02, 2019 at 02:30:41PM -0600, Steve French wrote:
> On Sat, Feb 2, 2019 at 12:17 PM Pavel Shilovsky <piastryyy@gmail.com> wrote:
> >
> > сб, 2 февр. 2019 г. в 10:13, Pavel Shilovsky <piastryyy@gmail.com>:
> > >
> > > сб, 2 февр. 2019 г. в 03:33, Greg KH <gregkh@linuxfoundation.org>:
> > > >
> > > > On Wed, Jan 30, 2019 at 04:07:30PM -0800, Pavel Shilovsky wrote:
> > > > > Commit 28eb24ff75c5 ("cifs: Always resolve hostname before reconnecting").
> > > > >
> > > > > In case a hostname resolves to a different IP address (e.g. long
> > > > > running mounts), make sure to resolve it every time prior to calling
> > > > > generic_ip_connect() in reconnect.
> > > > >
> > > > > This patch needs user space changes of cifs.upcall that set a timeout
> > > > > value for the "dns_resolver" key.
> > > >
> > > > Wait, you are requiring userspace to upgrade tools to support this?  And
> > > > you think that will happen to all systems running older kernels?
> > > >
> > > > This really feels like a new feature being added, what bug is this
> > > > fixing that requires it to be backported to all of the stable kernel
> > > > trees?
> > >
> > > Let's me describe what is going to happen without upgrade of the
> > > userspace tools. The 1st reconnect will cause proper resolving of DNS
> > > name and storing this name into the cache. All subsequent reconnects
> > > will use the value stored in the cache and do not attempt to resolve
> > > this DNS name. That means the fix will help partially but doesn't
> > > break anything.
> > >
> > > Once the userspace tools are upgraded, the cached DNS name will expire
> > > in 10 min, so every reconnect routine happening after that will use
> > > new IP. So, Linux distros will fully benefit from the patch once they
> > > upgrade the userspace tools but they do not need to synchronize
> > > updates of the kernel and the tools.
> > >
> > > The diff has been generated against the newest kernel but I checked
> > > that it cherry-picks to at least 4.4.y (and probably older ones).
> > >
> >
> > Adding Steve to comment on that.
> >
> > --
> > Best regards,
> > Pavel Shilovsky
> 
> Given the seriousness of the problem it fixes (hang on reconnect when
> server IP address changes) and that it could reduce possibility of
> data loss, this seems like it is reasonable to include in stable for
> kernels where it merges cleanly (which as Pavel noted may even include
> kernels older than 4.4).

Ok, thanks for the information, now queued up.

greg k-h