On Wed 24-02-10 10:57:59, Eric Sandeen wrote: > Dmitry Monakhov wrote: > > Jan Kara <jack@xxxxxxx> writes: > >>> The fact is that I've been able to reproduce the problem on LVM block > >>> devices, and sd* block devices so it's definitely not a loop device > >>> specific problem. > >>> > >>> By the way, I tried several other things other than "echo s > >>>> /proc/sysrq_trigger" I tried multiple sync followed with a one minute > >>> "sleep", > >>> > >>> "echo 3 >/proc/sys/vm/drop_caches" seems to lower the chances of "hash > >>> changes" but doesn't stops them. > >> Strange. When I use sync(1) in your script and use /dev/sda5 instead of a > >> /dev/loop0, I cannot reproduce the problem (was running the script for > >> something like an hour). > > Theoretically some pages may exist after rw=>ro remount > > because of generic race between write/sync, And they will be written > > in by writepage if page already has buffers. This not happen in ext4 > > because. Each time it try to perform writepages it try to start_journal > > and this result in EROFS. > > The race bug will be closed some day but new one may appear again. > > > > Let's be honest and change ext3 writepage like follows: > > - check ROFS flag inside write page > > - dump writepage's errors. > > > > > > sounds like the wrong approach to me, we really need to fix the root > cause and make remount,ro finish the job, I think. > > Throwing away writes which an application already thinks are completed > just because remount,ro didn't keep up sounds like a bad idea. I think > I would much rather have the write complete shortly after the readonly > transition, if I had to choose... Well, my opinion is that VFS should take care about the rw->ro transition so that it isn't racy... > I haven't looked at these paths at all but just hand-wavily, > remount,ro should follow pretty much the same path as freeze, > I think. And if freeze isn't getting everything on-disk we have > an even bigger problem. With freeze you can still keep dirty data in cache until the filesystem unfreezes so it's a different situation from rw->ro transition. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
