From: Dave Chinner <david@fromorbit.com>
To: Mateusz Guzik <mguzik@redhat.com>
Cc: "Lukáš Czerner" <lczerner@redhat.com>,
sandeen@redhat.com, "Jan Kara" <jack@suse.cz>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
"Josef Bacik" <jbacik@fb.com>,
"Al Viro" <viro@ZenIV.linux.org.uk>,
"Joe Perches" <joe@perches.com>
Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems
Date: Fri, 16 May 2014 08:21:35 +1000 [thread overview]
Message-ID: <20140515222135.GZ26353@dastard> (raw)
In-Reply-To: <20140515104746.GF10637@mguzik.redhat.com>
On Thu, May 15, 2014 at 12:47:48PM +0200, Mateusz Guzik wrote:
> On Thu, May 15, 2014 at 12:40:19PM +0200, Lukáš Czerner wrote:
> > On Wed, 14 May 2014, Eric Sandeen wrote:
> >
> > > Date: Wed, 14 May 2014 17:40:22 -0500
> > > From: Eric Sandeen <esandeen@redhat.com>
> > > Reply-To: sandeen@redhat.com
> > > To: Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>
> > > Cc: Mateusz Guzik <mguzik@redhat.com>, linux-kernel@vger.kernel.org,
> > > linux-fsdevel@vger.kernel.org, Josef Bacik <jbacik@fb.com>,
> > > Al Viro <viro@ZenIV.linux.org.uk>, Joe Perches <joe@perches.com>
> > > Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing
> > > filesystems
> > >
> > > On 5/14/14, 5:37 PM, Dave Chinner wrote:
> > > > On Thu, May 15, 2014 at 08:00:52AM +1000, Dave Chinner wrote:
> > > >> On Wed, May 14, 2014 at 01:39:45PM +0200, Jan Kara wrote:
> > > >>> On Wed 14-05-14 13:26:21, Mateusz Guzik wrote:
> > > >>>> On Wed, May 14, 2014 at 01:14:49PM +0200, Jan Kara wrote:
> > > >>>>> On Wed 14-05-14 00:04:43, Mateusz Guzik wrote:
> > > >>>>>> This helps hang troubleshooting efforts when only dmesg is available.
> > > >>>>>>
> > > >>>>>> While here remove code duplication with MS_RDONLY case and fix a
> > > >>>>>> whitespace nit.
> > > >>>>> I'm somewhat undecided here I have to say. On one hand I don't like
> > > >>>>> printing to kernel log when everything is fine and kernel is operating
> > > >>>>> normally. On the other hand I've seen quite a few cases where people have
> > > >>>>> shot themselves in the foot with filesystem freezing so having some trace
> > > >>>>> of this in the log doesn't seem like a completely bad thing either. What do
> > > >>>>> other people think?
> > > >>>>>
> > > >>>>
> > > >>>> I would like to note that the kernel already prints messages when e.g.
> > > >>>> filesystems get mounted.
> > > >>> Yeah, that's a fair point.
> > > >>
> > > >> But filesystems choose to output that info, not the VFS. When you do
> > > >> a remount,ro there is no output in syslog, because filesystems don't
> > > >> need to dump any output - the state change is reflected in
> > > >> /proc/self/mounts. IMO frozen should state should be communicated
> > > >> the same way so that it is silent when it just works, and the state
> > > >> can easily be determined when something goes wrong.
> > > >
> > > > Say, like this:
> > > >
> > > > $ grep /mnt/test /proc/mounts
> > > > /dev/vda /mnt/test xfs rw,relatime,attr2,inode64,noquota 0 0
> > > > $ sudo xfs_freeze -f /mnt/test
> > > > $ grep /mnt/test /proc/mounts
> > > > /dev/vda /mnt/test xfs rw,frozen,relatime,attr2,inode64,noquota 0 0
> > > > $ sudo xfs_freeze -u /mnt/test
> > > > $ grep /mnt/test /proc/mounts
> > > > /dev/vda /mnt/test xfs rw,relatime,attr2,inode64,noquota 0 0
> > > > $
> > >
> > > I'm not totally convinced that including a non-mount option in what
> > > has always (?) been a list of mount options is a great idea.
> >
> > I do not like it either. Mixing this together with other mount
> > options does not seem like a great idea, however we really need a
> > way to report this and I guess we can not just change the
> > /proc/self/mounts, or /proc/self/mountinfo format.
> >
> > So what about crating a new file /proc/self/frozen with the list of
> > frozen file systems in the same format what mounts, or mountinfo has
> > ?
> >
>
> As the time goes on there will be more data to present about given
> mountpoint. So either mountinfo should be extendable to support this
> (can't see why not) or new generic file with that property should be
> provided. I vote for the former.
>
> IOW, a new column in mountinfo. For frozen filesystems it would contain
> 'frozen_by=[%s]:[%d]' (escaped comm, pid).
I really don't see that the process that froze the filesystem is
particularly useful - it many cases that process is long gone (e.g.
fsfreeze is being used to allow a HW array to take a snapshot). Just
the fact it is in the process of freezing (if stuck, stack trace in
sysrq-w should be present) or frozen (freezing process may be long
gone, and is mostly irrelevant because you're now tracking down why
a thaw hasn't happened)...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2014-05-15 22:22 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-13 22:04 [PATCH V2 1/2] fs: include device name in error messages about freezing Mateusz Guzik
2014-05-13 22:04 ` [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems Mateusz Guzik
2014-05-14 11:14 ` Jan Kara
2014-05-14 11:26 ` Mateusz Guzik
2014-05-14 11:39 ` Jan Kara
2014-05-14 22:00 ` Dave Chinner
2014-05-14 22:37 ` Dave Chinner
2014-05-14 22:40 ` Eric Sandeen
2014-05-15 10:40 ` Lukáš Czerner
2014-05-15 10:47 ` Mateusz Guzik
2014-05-15 22:21 ` Dave Chinner [this message]
2014-05-15 22:34 ` Mateusz Guzik
2014-05-15 22:51 ` Dave Chinner
2014-05-15 23:19 ` Mateusz Guzik
2014-05-16 0:11 ` Dave Chinner
2014-05-16 0:39 ` Mateusz Guzik
2014-05-19 9:43 ` Jan Kara
2014-05-19 23:37 ` Dave Chinner
2014-05-15 10:13 ` Jan Kara
2014-05-15 22:16 ` Dave Chinner
2014-05-14 11:58 ` Lukáš Czerner
2014-05-14 11:10 ` [PATCH V2 1/2] fs: include device name in error messages about freezing Jan Kara
2014-05-14 22:07 ` Dave Chinner
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