Jan Kara <jack@xxxxxxx> writes: > 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. Off course, but still. This is just a sanity check. Similar check in ext4 help me to find the generic issue. Off course it have to be guarded by unlikely() statement >> >> 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... No, My patch just try to nail the RO semantics in to writepage. Since other places are already guarded by start_journal, writepage is the only one which may has weakness. About ENOSPC/EDQUOT spam. It may be not bad to print a error message for crazy person who use mmap for space file. > >> 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. In fact freeze is also not absolutely io proof :) When i've worked on COW device i use freeze-fs for consistent image creation, And sometimes after filesystem was friezed i still get bios. We do not investigate this too deeply and just queue bios in to pending queue. > > Honza -- 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
