On Sun, Jan 24, 2010 at 02:41:15PM +0300, Dmitry Monakhov wrote: > Currently on rw=>ro remount we have following race > | mount /mnt -oremount,ro | write-task | > |-------------------------+------------| > | | open(RDWR) | > | shrink_dcache_sb(sb); | | > | sync_filesystem(sb); | | > | | write() | > | | close() | > | fs_may_remount_ro(sb) | | > | sb->s_flags = new_flags | | > Later writeback or sync() will result in error due to MS_RDONLY flag > In case of ext4 this result in jbd2_start failure on writeback > ext4_da_writepages: jbd2_start: 1024 pages, ino 1431; err -30 > In fact all others are affected by this error but it is not visible > because the skip s_flags check on writeback. For example ext3 check > (s_flags & MS_RDONLY) only if page has no buffers during journal start. > > In order to prevent the race we have to block new writers before > fs_may_remount_ro() and sync_filesystem(). Let's introduce new > sb->s_flags MS_RO_REMOUNT flag for this purpose. But suddenly we have > no available space in MS_XXX bits, let's share this bit with MS_REMOUNT. > This is possible because MS_REMOUNT used only for passing arguments > from flags to sys_mount() and never used in sb->s_flags. It's not a solution. You get an _attempted_ remount ro making writes fail, even if it's going to be unsuccessful. No go... -- 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
