linux-kernel - RE: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs

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Message-ID: <KL1P15301MB0343C783FAA171868E45619C94559@KL1P15301MB0343.APCP153.PROD.OUTLOOK.COM>
Date:   Sun, 9 May 2021 10:16:06 +0000
From:   Shyam Prasad <Shyam.Prasad@...rosoft.com>
To:     Salvatore Bonaccorso <carnil@...ian.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Paulo Alcantara <palcantara@...e.de>
CC:     pc <pc@....nz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Aurelien Aptel <aaptel@...e.com>,
        Steven French <Steven.French@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>
Subject: RE: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set
 CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.

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@...il.com> On Behalf Of Salvatore Bonaccorso
Sent: Saturday, May 8, 2021 6:52 PM
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Shyam Prasad <Shyam.Prasad@...rosoft.com>; pc <pc@....nz>; linux-kernel@...r.kernel.org; stable@...r.kernel.org; Aurelien Aptel <aaptel@...e.com>; Steven French <Steven.French@...rosoft.com>; Sasha Levin <sashal@...nel.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

Download attachment "0001-cifs-fix-prefix-path-in-dfs-mounts.patch" of type "application/octet-stream" (1160 bytes)