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

Jan Kara
2014-05-15T13:46:16Z

On Thu 15-05-14 08:47:25, Ted Tso wrote:
> 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)?
By 'superblock' I meant 'struct super_block' ;) So we are in agreement I
believe.

> 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.
I was thinking about this as well but all these "warn after X seconds"
warnings tend to have quite a few false positives in practice so dumping
this in emergency-thaw sysrq handler or exposing the information somewhere
in proc (e.g. mountinfo) would look like a better option to me.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR