From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tsutomu Itoh Subject: [BUG] umount command doesn't end forever Date: Fri, 02 Sep 2011 17:33:57 +0900 Message-ID: <4E6094F5.8000506@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP To: Linux Btrfs Return-path: List-ID: In current for-linus branch, I encountered the problem that the umount command doesn't end forever. ================================= # mount ... /dev/sdc9 on /test9 type btrfs (rw,space_cache,compress=lzo,autodefrag) # umount /test9 crash> ps | grep umount 13107 6558 0 ffff8801257296c0 UN 0.0 105132 672 umount crash> bt 13107 PID: 13107 TASK: ffff8801257296c0 CPU: 0 COMMAND: "umount" #0 [ffff88016bb4fce8] schedule at ffffffff813a0c76 #1 [ffff88016bb4fd90] close_ctree at ffffffffa0386b3c [btrfs] #2 [ffff88016bb4fe00] btrfs_put_super at ffffffffa036bc0c [btrfs] #3 [ffff88016bb4fe20] generic_shutdown_super at ffffffff8111260e #4 [ffff88016bb4fe50] kill_anon_super at ffffffff811126fb #5 [ffff88016bb4fe70] deactivate_locked_super at ffffffff81112c9b #6 [ffff88016bb4fe90] deactivate_super at ffffffff81113673 #7 [ffff88016bb4feb0] mntput_no_expire at ffffffff81128973 #8 [ffff88016bb4fee0] sys_umount at ffffffff811294ee #9 [ffff88016bb4ff80] system_call_fastpath at ffffffff813a9182 RIP: 00007fd8f08cb5d7 RSP: 00007fffe85dea40 RFLAGS: 00010246 RAX: 00000000000000a6 RBX: ffffffff813a9182 RCX: 0000000000000006 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007fd8f17a9b90 RBP: 00007fd8f17a9b70 R8: 0000000000000005 R9: 0000000000000000 R10: 00007fffe85df220 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007fffe85df688 R15: 00007fd8f17a9c00 ORIG_RAX: 00000000000000a6 CS: 0033 SS: 002b crash> ps | grep clean ... 6610 2 1 ffff8801945ac440 UN 0.0 0 0 [btrfs-cleaner] crash> bt 6610 PID: 6610 TASK: ffff8801945ac440 CPU: 1 COMMAND: "btrfs-cleaner" #0 [ffff880194565958] schedule at ffffffff813a0c76 #1 [ffff880194565a00] rwsem_down_failed_common at ffffffff813a2453 #2 [ffff880194565a60] rwsem_down_read_failed at ffffffff813a24ac #3 [ffff880194565a70] call_rwsem_down_read_failed at ffffffff811c60d4 #4 [ffff880194565ad8] writeback_inodes_sb_nr_if_idle at ffffffff8112ee46 #5 [ffff880194565b08] reserve_metadata_bytes at ffffffffa03772d9 [btrfs] #6 [ffff880194565c08] btrfs_delalloc_reserve_metadata at ffffffffa0378196 [btrfs] #7 [ffff880194565c58] btrfs_delalloc_reserve_space at ffffffffa037c2ed [btrfs] #8 [ffff880194565c88] btrfs_defrag_file at ffffffffa03ad400 [btrfs] #9 [ffff880194565dc8] btrfs_run_defrag_inodes at ffffffffa0397125 [btrfs] #10 [ffff880194565e68] cleaner_kthread at ffffffffa0384844 [btrfs] #11 [ffff880194565ee8] kthread at ffffffff810608ac #12 [ffff880194565f48] kernel_thread_helper at ffffffff813aa2a4 ================================= umount acquires down_write(&s->s_umount) by deactivate_super() and waits for the end of btrfs-cleaner. But, btrfs-cleaner stops because of the acquisition waiting of down_read(&sb->s_umount) by writeback_inodes_sb_nr_if_idle(). So, the deadlock has happened, I think. -Tsutomu