On Wed, Sep 7, 2011 at 1:34 PM, Jan Kara <jack@xxxxxxx> wrote: > Hello, > > Thanks for report! > > On Wed 07-09-11 12:29:30, Masayoshi MIZUMA wrote: >> When I checked the freeze feature for ext3 filesystem using fsfreeze >> command at 3.1.0-rc4, I think the following deadlock problem happened. >> >> How to reproduce: >> # mkfs -t ext3 /dev/sdd1 >> # mount /dev/sdd1 /MNT >> # ./fsstress -d /MNT/tmp -n 10 -p 1000 > /dev/null 2>&1 & >> # fsfreeze -f /MNT >> # fsfreeze -u /MNT >> >> If this deadlock is reproduced, "fsfreeze -u /MNT" does not return. >> >> The detail of deadlock: >> o [flush-8:16:1523] >> wb_do_writeback >> wb_writeback >> ... >> ext3_journalled_writepage >> journal_start >> start_this_handle >> # waiting until journal->j_barrier_count turns 0... >> # j_barrier_count was incremented by journal_lock_updates() >> # via ext3_freeze(). >> >> o [fsstress:2673] >> sys_sync >> sync_filesystems >> iterate_supers >> down_read(sb->s_umount) >> sync_one_sb >> __sync_filesystem >> writeback_inodes_sb >> writeback_inodes_sb_nr >> wait_for_completion >> wait_for_common >> # waiting for completion of [flush-8:16:1523]... >> >> o [fsfreeze:2749] >> sys_ioctl >> do_vfs_ioctl >> thaw_super >> # waiting for down_write(sb->s_umount)... >> # [fsfreeze:2673] did down_read(sb->s_umount). > Yes, this is a classical deadlock that can happen for any filesystem. The > problem is flusher thread holds s_umount semaphore (either directly, or as > in your case, indirectly via blocked sync) and tries to do some IO which > blocks on frozen filesystem. It's particularly easy to hit for ext3 because > it doesn't do vfs_check_frozen() checks but all other filesystems have the > race window as well. Val Henson is working on fixing the problem - she even > has some first version of patches I believe. > > Honza xfstests test 068 has been around since kernel 2.4 days and should have caught it if xfs is impacted. I know I ran the 2002 version many times to prove to myself that fsfreeze for xfs was stable when teamed with LVM. (It wasn't when I first wrote 068 way back then). 068 has been greatly simplified since 2002, but it still looks like it should do a good job. Is there a problem with 068? Does it need extra test coverage even for xfs? Greg -- 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
