linux-kernel - Re: Possible bug report: kernel 6.5.0/6.5.1 high load when CIFS share is mounted (cifsd-cfid-laundromat in"D" state)

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Message-ID: <CAO+kfxTvA6N=i+jGf0XbSyqf85i=q+vR6R9d_42OWfM2sWWXaA@mail.gmail.com>
Date:   Mon, 18 Sep 2023 18:55:58 -0400
From:   Brian Pardy <brian.pardy@...il.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Linux CIFS <linux-cifs@...r.kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Steve French <sfrench@...ba.org>
Subject: Re: Possible bug report: kernel 6.5.0/6.5.1 high load when CIFS share
 is mounted (cifsd-cfid-laundromat in"D" state)

[RS removed from CC due to bounce message]

On Wed, Sep 6, 2023 at 5:03 PM Brian Pardy <brian.pardy@...il.com> wrote:
> On Tue, Sep 5, 2023 at 9:01 PM Bagas Sanjaya <bagasdotme@...il.com> wrote:
> > Thanks for the regression report. But if you want to get it fixed,
> > you have to do your part: perform bisection. See Documentation/admin-guide/bug-bisect.rst in the kernel sources for how to do that.
> >
> > Anyway, I'm adding it to regzbot:
> >
> > #regzbot ^introduced: v6.4..v6.5
> > #regzbot title: incorrect CPU utilization report (multiplied) when mounting CIFS
>
> Thank you for directing me to the bug-bisect documentation. Results below:
>
> # git bisect bad
> d14de8067e3f9653cdef5a094176d00f3260ab20 is the first bad commit
> commit d14de8067e3f9653cdef5a094176d00f3260ab20
> Author: Ronnie Sahlberg <lsahlber@...hat.com>
> Date:   Thu Jul 6 12:32:24 2023 +1000
>
>     cifs: Add a laundromat thread for cached directories
>
>     and drop cached directories after 30 seconds
>
>     Signed-off-by: Ronnie Sahlberg <lsahlber@...hat.com>
>     Signed-off-by: Steve French <stfrench@...rosoft.com>
>
>  fs/smb/client/cached_dir.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++
>  fs/smb/client/cached_dir.h |  1 +
>  2 files changed, 68 insertions(+)

Is there any further information I can provide to aid in debugging
this issue? Should I just expect incorrect load average reporting when
a CIFS share is mounted on any kernel >6.5.0?

I'm not clear on the value or necessity of this "laundromat thread" -
everything worked as expected before it was added - shall I just patch
it out of my kernel builds going forward if there is no interest in
fixing it? Is a .config option to disable it possible?