[Bug 620242] [NEW] hang in ext4_journal_start_sb making an lvm snapshot

[Martin Pool]

Public bug reported:

[maverick] 
I'm trying to use lvm snapshots under schroot to create a reproducible build environment.  The first few uses of them worked, but after that I find more and more processes are getting locked up like this:


[168841.490770] INFO: task flush-252:13:27159 blocked for more than 120 seconds.
[168841.490777] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[168841.490783] flush-252:13  D 000000010100cf86     0 27159      2 0x00000000
[168841.490793]  ffff8801f6643ac0 0000000000000046 ffff880100000000 0000000000015900
[168841.490802]  ffff8801f6643fd8 0000000000015900 ffff8801f6643fd8 ffff88008269c4a0
[168841.490810]  0000000000015900 0000000000015900 ffff8801f6643fd8 0000000000015900
[168841.490818] Call Trace:
[168841.490831]  [<ffffffff81201aad>] ext4_journal_start_sb+0x7d/0x130
[168841.490841]  [<ffffffff8107e490>] ? autoremove_wake_function+0x0/0x40
[168841.490850]  [<ffffffff811ef6ff>] ext4_da_writepages+0x25f/0x640
[168841.490859]  [<ffffffff810530e6>] ? load_balance_fair+0x1a6/0x2a0
[168841.490869]  [<ffffffff81109ea1>] do_writepages+0x21/0x40
[168841.490877]  [<ffffffff81173db6>] writeback_single_inode+0xe6/0x3f0
[168841.490884]  [<ffffffff81174525>] writeback_sb_inodes+0x195/0x280
[168841.490892]  [<ffffffff81174f7c>] wb_writeback+0x12c/0x2b0
[168841.490900]  [<ffffffff8106ef4c>] ? lock_timer_base+0x3c/0x70
[168841.490908]  [<ffffffff8106fa42>] ? del_timer_sync+0x22/0x30
[168841.490915]  [<ffffffff811751a9>] wb_do_writeback+0xa9/0x190
[168841.490922]  [<ffffffff8106f060>] ? process_timeout+0x0/0x10
[168841.490930]  [<ffffffff811752e7>] bdi_writeback_task+0x57/0x160
[168841.490936]  [<ffffffff8107e357>] ? bit_waitqueue+0x17/0xd0
[168841.490945]  [<ffffffff81119406>] bdi_start_fn+0x86/0x100
[168841.490952]  [<ffffffff81119380>] ? bdi_start_fn+0x0/0x100
[168841.490957]  [<ffffffff8107df36>] kthread+0x96/0xa0
[168841.490965]  [<ffffffff8100aee4>] kernel_thread_helper+0x4/0x10
[168841.490971]  [<ffffffff8107dea0>] ? kthread+0x0/0xa0
[168841.490977]  [<ffffffff8100aee0>] ? kernel_thread_helper+0x0/0x10
[168841.490984] INFO: task lvcreate:27338 blocked for more than 120 seconds.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

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hang in ext4_journal_start_sb making an lvm snapshot
https://bugs.launchpad.net/bugs/620242
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