On Wed 24-02-10 19:01:27, 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. OK, I see that in theory a process can open file for writing after fs_may_remount_ro() before MS_RDONLY flag gets set. That could be really nasty. But by no means we should solve this VFS problem by spilling error messages from the filesystem. Especially because block_write_full_page can fail from a number of legal reasons (ENOSPC, EDQUOT, EIO) and we don't want to pollute logs with such stuff. BTW: This isn't the race Camille could see because he did all the writes, then sync and then remount-ro... Al, Christoph, do I miss something or there is really nothing which prevents a process from opening a file after the fs_may_remount_ro() check in do_remount_sb()? Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
