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: <83d00d50bc628a85db71adb440d8afb5@matoro.tk>
Date:   Fri, 13 Oct 2023 19:19:37 -0400
From:   matoro <matoro_mailinglist_kernel@...oro.tk>
To:     "Dr. Bernd Feige" <bernd.feige@...klinik-freiburg.de>
Cc:     tom@...pey.com, smfrench@...il.com, paul@...krain42.org,
        linux-cifs@...r.kernel.org, bagasdotme@...il.com,
        regressions@...ts.linux.dev, pc@...guebit.com,
        ronniesahlberg@...il.com, nspmangalore@...il.com,
        brian.pardy@...il.com, bharathsm@...rosoft.com,
        linux-kernel@...r.kernel.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)

On 2023-10-05 05:55, Dr. Bernd Feige wrote:
> Am Dienstag, dem 26.09.2023 um 17:54 -0700 schrieb Paul Aurich:
>> Perhaps the laundromat thread should be using msleep_interruptible()?
>> 
>> Using an interruptible sleep appears to prevent the thread from
>> contributing
>> to the load average, and has the happy side-effect of removing the
>> up-to-1s delay
>> when tearing down the tcon (since a7c01fa93ae, kthread_stop() will
>> return
>> early triggered by kthread_stop).
> 
> Sorry for chiming in so late - I'm also on gentoo (kernel 6.5.5-
> gentoo), but as a client of Windows AD.
> 
> Just want to emphasize that using uninterruptible sleep has not just
> unhappy but devastating side-effects.
> 
> I have 8 processors and 16 cifsd-cfid-laundromat processes, so
> /proc/loadavg reports a load average of 16 on a totally idle system.
> 
> This means that load-balancing software will never start additional
> tasks on this system - "make -l" but also any other load-dependent
> system. Just reducing the number of cifsd-cfid-laundromat processes
> does not fix this - even a single one makes loadavg report a wrong
> result for load balancing.
> 
> So, if cifsd-cfid-laundromat must really be uninterruptible, the only
> solution would be to change the way loadavg is computed by the kernel
> to exclude uninterruptible but sleeping processes. But must it be
> uninterruptible?
> 
> Thanks and best regards,
> Bernd

This is a huge problem here as well, as a client to Samba using SMB1 
(for Unix extensions).

For others encountering this problem, I was able to work around it with 
the following snippet:

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index 2d5e9a9d5b8b..fc2caccb597a 100644
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -576,7 +576,7 @@ cifs_cfids_laundromat_thread(void *p)
         struct list_head entry;

         while (!kthread_should_stop()) {
-               ssleep(1);
+               msleep_interruptible(1000);
                 INIT_LIST_HEAD(&entry);
                 if (kthread_should_stop())
                         return 0;