Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

Mark Lord
2007-06-07T21:39:12Z

Andrew Morton wrote:
> On Thu, 07 Jun 2007 12:11:58 -0400
> Chuck Ebbert <cebbert@redhat.com> wrote:
>
>> On 06/07/2007 11:41 AM, Andrew Morton wrote:
>>>> mount /var/lib/mythtv -oremount,ro
>>>> sync
>>>> umount /var/lib/mythtv
>>> Did this succeed? If the application is still truncating that file, the
>>> umount should have failed.
>> Shouldn't sync should wait for truncate to finish?
>
> I can't think of anything in there at present which would cause that to
> happen, and it's not immediately obvious how we _could_ make it happen - we
> have an inode which potentially has no dirty pages and which is itself
> clean. The truncate can span multiple journal commits, so forcing a
> journal commit in sync() won't necessarily block behind the truncate.
>
> I guess we could ask sync to speculatively take and release every inode's
> i_mutex or something. But even that would involve quite some hoop-jumping
> due to those infuriating spinlock-protected list_heads on the superblock.
>
> hmm.

Yeah, I really don't know what to do with this either.
We have to have a bounds on how long we wait at shutdown,
but there doesn't seem to be an easy way to get notified
once a filesystem becomes idle (?).

I suppose I could have the script loop on /proc/interrupts until
it sees the disk activity has tapered off..

Cheers