On Thu 23-04-09 07:10:40, Christoph Hellwig wrote: > On Wed, Apr 22, 2009 at 05:56:20PM +0200, Jan Kara wrote: > > So far, do_sync() called: > > sync_inodes(0); > > sync_supers(); > > sync_filesystems(0); > > sync_filesystems(1); > > sync_inodes(1); > > > > This ordering makes it kind of hard for filesystems as sync_inodes(0) need not > > submit all the IO (for example it skips inodes with I_SYNC set) so e.g. forcing > > transaction to disk in ->sync_fs() is not really enough. Therefore sys_sync has > > not been completely reliable on some filesystems (ext3, ext4, reiserfs, ocfs2 > > and others are hit by this) when racing e.g. with background writeback. A > > similar problem hits also other filesystems (e.g. ext2) because of > > write_supers() being called before the sync_inodes(1). > > > > Change the ordering of calls in do_sync() - this requires a new function > > sync_blkdevs() to preserve the property that block devices are always synced > > after write_super() / sync_fs() call. > > > > The same issue is fixed in __fsync_super() function used on umount / > > remount read-only. > > This looks reasonable, but I always fear we break something when > touching this path. It would be really nice if we could rewrite do_sync > to sit ontop of __fsync_super. E.g. do a > > for_each_sb() > __fsync_super(sb, ASYNC); > for_each_sb() > __fsync_super(sb, SYNC); > > so that we have one central place that makes sure a filesystem is > properly synced. OK, makes sence. Will do. > Another thing I want to do in this area is sort out the meaning of > write_super. I'd really prefer to have every filesystem implement > ->sync_fs for actual data-integerity syncs, and only leave ->write_super > for the periodic writeouts, as the current implementation is extrenly > confusing and causes a lot of trouble for filesystems doing their own > periodic sb writeback. Yes, that would be nice but I guess it's a partly a separate issue (and has to touch a lot of filesystems). I'll keep write_supers() call in the next version of the patch so that this split isn't made harded by it. 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
