Hi Salvatore,

Thanks for reminding me. I had to do some reading to reply to this one. 
The situation right now is this:
The patch "cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath." has been reverted. Which means that the DFS bug which you originally faced will not be seen. 

Hi Greg,

Here are the two patches which I'm referring to:
1. cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.12&id=a738c93fb1c17e386a09304b517b1c6b2a6a5a8b
This fixed an issue when two cifs mount points shared a common prefix in the path which they mounted from the same server. The patch was marked for CC:stable considering that this fix can be important for some users.
However, there was a dependent change for DFS scenario, which is present in the Linus' mainline tree, but were not marked for CC:stable, so missing from the stable trees.
Due to the missing dependent changes, DFS users faced issues with pre-5.11 kernels, and this patch was reverted in the stable trees.

2. Due to a major change that went into the 5.11 kernel (the new mount API support), the code differs significantly, and the missing patch cannot be applied to pre-5.11 trees.
Hence, Paulo submitted the attached patch (cifs: fix prefix path in dfs mounts), which fixes this for pre-5.11 kernels.

I was referring to these two patches to be applied to all stable trees. Salvatore has verified that with both patches applied, the DFS scenario starts working again. 
@Paulo Alcantara Please add if I missed something here. 

Regards,
Shyam

-----Original Message-----
From: Salvatore Bonaccorso <salvatore.bonaccorso@gmail.com> On Behalf Of Salvatore Bonaccorso
Sent: Saturday, May 8, 2021 6:52 PM
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Shyam Prasad <Shyam.Prasad@microsoft.com>; pc <pc@cjr.nz>; linux-kernel@vger.kernel.org; stable@vger.kernel.org; Aurelien Aptel <aaptel@suse.com>; Steven French <Steven.French@microsoft.com>; Sasha Levin <sashal@kernel.org>
Subject: Re: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.

Shyam, Paulo,

On Fri, Apr 23, 2021 at 09:42:35AM +0200, Greg Kroah-Hartman wrote:
> On Thu, Apr 22, 2021 at 03:36:07PM +0000, Shyam Prasad wrote:
> > Hi Salvatore and Santiago,
> > 
> > Thanks for testing this out.
> > 
> > @Greg Kroah-Hartman: The reverted patch used in combination with Paulo's fix seems to fix both use cases. 
> > Can we have both these taken in on stable kernels? Paulo's patch is needed only for kernels 5.10 and older.
> 
> I do not know what "both" is here at all.
> 
> Please resubmit all of the needed commits in a format that I can apply 
> them in, and I will be glad to review them and queue them up.
> 
> Note, patches that are not in Linus's tree better be documented really 
> really really really well for why that is not so...

Did you saw the ping from Greg? Otherwise I think the situation as it is now for the older stable series is probably just as fine as it is now with the repsective original commit reverted.

Regards,
Salvatore