linux-kernel - Re: [PATCH] Re: filesystem being remounted supports timestamps until 2038

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Date:   Thu, 27 Jan 2022 22:49:50 +0100
From:   Salvatore Bonaccorso <carnil@...ian.org>
To:     Christian Kujau <lists@...dbynature.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] Re: filesystem being remounted supports timestamps until
 2038

Hi,

On Tue, Jun 23, 2020 at 05:26:49PM -0700, Christian Kujau wrote:
> On Sat, 4 Jan 2020, Christian Kujau wrote:
> > On Sun, 29 Dec 2019, Linus Torvalds wrote:
> > > >     When file systems are remounted a couple of times per day (e.g. rw/ro for backup
> > > >     purposes), dmesg gets flooded with these messages. Change pr_warn into pr_debug
> > > >     to make it stop.
> > > 
> > > How about just doing it once per mount?
> > 
> > Yes, once per mount would work, and maybe not print a warning on remounts 
> > at all.
> 
> Is there any chance that this can be revisited perhaps? This is still 
> flooding my dmesg just because I have that (curde?) mechanism in place to 
> remount the backup device after the hourly backup-run to read-only. Sure, 
> I could omit that ("Doc, it hurts when I do that", as Al would comment), 
> but that's really the only repeating message that gets triggered because 
> of this. 1067 messages in ~60 days of uptime :-|
> 
> Does the patch below make any sense, would that work?
> 
> Please reconsider,
> Christian.
> 
> > Commit f8b92ba67c5d ("mount: Add mount warning for impending timestamp 
> > expiry") introduced:
> > 
> >    Mounted %s file system at %s supports timestamps until [...]
> > 
> > in mnt_warn_timestamp_expiry(), but then 0ecee6699064 ("fs/namespace.c: 
> > fix use-after-free of mount in mnt_warn_timestamp_expiry") changed this to
> > 
> >   %s filesystem being %s at %s supports timestamps until [...]
> > 
> > in order to fix a use-after-free.
> > 
> > > Of course, if you actually unmount and completely re-mount a
> > > filesystem, then that would still warn multiple times, but at that
> > > point I think it's reasonable to do.
> > 
> > Yes, of course. Umount/remount cycles should still issue a warning, but 
> > "-o remount" should not, IMHO.
> > 
> > Thanks,
> > Christian.
> 
> commit c9a5338b4930cdf99073042de0717db43d7b75be
> Author: Christian Kujau <lists@...dbynature.de>
> Date:   Thu Dec 26 17:39:57 2019 -0800
> 
>     Commit f8b92ba67c5d ("mount: Add mount warning for impending timestamp expiry") resp.
>     0ecee6699064 ("fix use-after-free of mount in mnt_warn_timestamp_expiry()") introduced
>     a pr_warn message and the following gets sent to dmesg on every remount:
>     
>      [...] filesystem being remounted at /mnt supports timestamps until 2038 (0x7fffffff)
>     
>     When file systems are remounted a couple of times per day (e.g. rw/ro for backup
>     purposes), dmesg gets flooded with these messages. Change pr_warn into pr_debug
>     to make it stop.
>     
>     Signed-off-by: Christian Kujau <lists@...dbynature.de>
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index be601d3a8008..afc6a13e7316 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2478,7 +2478,7 @@ static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *
>  
>  		time64_to_tm(sb->s_time_max, 0, &tm);
>  
> -		pr_warn("%s filesystem being %s at %s supports timestamps until %04ld (0x%llx)\n",
> +		pr_debug("%s filesystem being %s at %s supports timestamps until %04ld (0x%llx)\n",
>  			sb->s_type->name,
>  			is_mounted(mnt) ? "remounted" : "mounted",
>  			mntpath,

This is somehow prompted by a recent update in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996876#46 . 

The discussion on the above seems to have stalled, is this still
something worth persuing or should it be further ignored?

Regards,
Salvatore