linux-kernel - Re: [PATCH 2/2] fs: print a message when freezing/unfreezing filesystems

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Message-ID: <20140515124725.GA8194@thunk.org>
Date:	Thu, 15 May 2014 08:47:25 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Mateusz Guzik <mguzik@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Josef Bacik <jbacik@...com>, Al Viro <viro@...IV.linux.org.uk>,
	Eric Sandeen <esandeen@...hat.com>
Subject: Re: [PATCH 2/2] fs: print a message when freezing/unfreezing
 filesystems

On Thu, May 15, 2014 at 12:01:57PM +0200, Jan Kara wrote:
>   I was tracking down a couple of times what the hell is freezing the
> filesystem (and not unfreezing it) and I agree with Mateusz it would be
> nice if we could tell after the fact who froze the fs. Maybe we could store
> that information in superblock and dump it during emergency thaw?

Saving it in the superblock would require changing a bunch of file
systems.  What if we store this information in memory, and print it
out under certain conditions (i.e., after a soft lockup detection, or
upon request of some magic sysrq request)?

Or we could create a tunable threshold and print a message after a
file system has been frozen more than a particular specified duration,
with that duration set conservatively to something like 60 or 120
seconds by default.

						- Ted
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