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Subject[RFH] 4.9.52: task blocked for more than 300 seconds - xen_clocksource_get_cycles?
Date
Hello,

in a VM running linux-4.9.52 on Debian-Wheezy with Xen-4.1 I observed
several stuck processes: Here is one (truncated) dump of the Linux
kernel messages:

> [<ffffffff8160db6d>] ? __schedule+0x23d/0x6d0
> [<ffffffff8160e8a0>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160e032>] ? schedule+0x32/0x80
> [<ffffffff8161150c>] ? schedule_timeout+0x1ec/0x360
> [<ffffffff8130f277>] ? __blk_mq_run_hw_queue+0x327/0x3e0
*** see below
> [<ffffffff8101b7f1>] ? xen_clocksource_get_cycles+0x11/0x20
> [<ffffffff8160e8a0>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160d8b4>] ? io_schedule_timeout+0xb4/0x130
> [<ffffffff810bb6f7>] ? prepare_to_wait+0x57/0x80
> [<ffffffff8160e8b7>] ? bit_wait_io+0x17/0x60
> [<ffffffff8160e3ac>] ? __wait_on_bit+0x5c/0x90
> [<ffffffff8160e8a0>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160e50e>] ? out_of_line_wait_on_bit+0x7e/0xa0
> [<ffffffff810bba20>] ? autoremove_wake_function+0x40/0x40
> [<ffffffffc00abd18>] ? jbd2_journal_commit_transaction+0xd48/0x17e0 [jbd2]
> [<ffffffff810247d9>] ? __switch_to+0x2c9/0x720
> [<ffffffff810e67fd>] ? try_to_del_timer_sync+0x4d/0x80
> [<ffffffffc00b099d>] ? kjournald2+0xdd/0x280 [jbd2]
> [<ffffffff810bb9e0>] ? wake_up_atomic_t+0x30/0x30
> [<ffffffffc00b08c0>] ? commit_timeout+0x10/0x10 [jbd2]
> [<ffffffff81097660>] ? kthread+0xf0/0x110
> [<ffffffff810247d9>] ? __switch_to+0x2c9/0x720
> [<ffffffff81097570>] ? kthread_park+0x60/0x60
> [<ffffffff81612bb5>] ? ret_from_fork+0x25/0x30
> NMI backtrace for cpu 2
> CPU: 2 PID: 35 Comm: khungtaskd Not tainted 4.9.0-ucs105-amd64 #1 Debian 4.9.30-2A~4.2.0.201709271649
> 0000000000000000 ffffffff81331935 0000000000000000 0000000000000002
> ffffffff81335e60 0000000000000002 ffffffff8104cb70 ffff8801f0c90e80
> ffffffff81335f6a ffff8801f0c90e80 00000000003fffbc ffffffff81128048
> Call Trace:
> [<ffffffff81331935>] ? dump_stack+0x5c/0x77
> [<ffffffff81335e60>] ? nmi_cpu_backtrace+0x90/0xa0
> [<ffffffff8104cb70>] ? irq_force_complete_move+0x140/0x140
> [<ffffffff81335f6a>] ? nmi_trigger_cpumask_backtrace+0xfa/0x130
> [<ffffffff81128048>] ? watchdog+0x2b8/0x330
> [<ffffffff81127d90>] ? reset_hung_task_detector+0x10/0x10
> [<ffffffff81097660>] ? kthread+0xf0/0x110
> [<ffffffff810247d9>] ? __switch_to+0x2c9/0x720
> [<ffffffff81097570>] ? kthread_park+0x60/0x60
> [<ffffffff81612bb5>] ? ret_from_fork+0x25/0x30
> Sending NMI from CPU 2 to CPUs 0-1,3:
> NMI backtrace for cpu 1
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0-ucs105-amd64 #1 Debian 4.9.30-2A~4.2.0.201709271649
> task: ffff8801f4a02ec0 task.stack: ffffc90040ca4000
> RIP: e030:[<ffffffff810013aa>] [<ffffffff810013aa>] xen_hypercall_sched_op+0xa/0x20
> RSP: e02b:ffffc90040ca7ed0 EFLAGS: 00000246
> RAX: 0000000000000000 RBX: ffff8801f4a02ec0 RCX: ffffffff810013aa
> RDX: ffffffff81c4ba70 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000007ff0 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: ffff8801f4a02ec0 R15: ffff8801f4a02ec0
> FS: 00007f23ac595700(0000) GS:ffff8801f5a80000(0000) knlGS:0000000000000000
> CS: e033 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00007f52537d6d46 CR3: 00000001bba23000 CR4: 0000000000002660
> Stack:
> ffff8801bb832201 0000000000000001 ffffffff8101b55c ffffffff81611ec8
> ffff8801f4a02ec0 0000000000000001 ffffffff810bc280 ffff8801f4a02ec0
> ffff8801f4a02ec0 c0a995961d41240f addce6dcadd009c9 0000000000000000
> Call Trace:
> [<ffffffff8101b55c>] ? xen_safe_halt+0xc/0x20
> [<ffffffff81611ec8>] ? default_idle+0x18/0xd0
> [<ffffffff810bc280>] ? cpu_startup_entry+0x1f0/0x260
> Code: cc 51 41 53 b8 1c 00 00 00 0f 05 41 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> NMI backtrace for cpu 3
> CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.9.0-ucs105-amd64 #1 Debian 4.9.30-2A~4.2.0.201709271649
> task: ffff8801f4a24f00 task.stack: ffffc90040cb4000
> RIP: e030:[<ffffffff810013aa>] [<ffffffff810013aa>] xen_hypercall_sched_op+0xa/0x20
> RSP: e02b:ffffc90040cb7ed0 EFLAGS: 00000246
> RAX: 0000000000000000 RBX: ffff8801f4a24f00 RCX: ffffffff810013aa
> RDX: ffffffff81c4ba70 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000007ff0 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: ffff8801f4a24f00 R15: ffff8801f4a24f00
> FS: 00007f1a2af19700(0000) GS:ffff8801f5b80000(0000) knlGS:0000000000000000
> CS: e033 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00007f4a5416b000 CR3: 00000001d83ec000 CR4: 0000000000002660
> Stack:
> 0000000000000001 0000000000000001 ffffffff8101b55c ffffffff81611ec8
> ffff8801f4a24f00 0000000000000003 ffffffff810bc280 ffff8801f4a24f00
> ffff8801f4a24f00 77816deb133b9979 addce6dcadd009c9 0000000000000000
> Call Trace:
> [<ffffffff8101b55c>] ? xen_safe_halt+0xc/0x20
> [<ffffffff81611ec8>] ? default_idle+0x18/0xd0
> [<ffffffff810bc280>] ? cpu_startup_entry+0x1f0/0x260
> Code: cc 51 41 53 b8 1c 00 00 00 0f 05 41 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> NMI backtrace for cpu 0
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.0-ucs105-amd64 #1 Debian 4.9.30-2A~4.2.0.201709271649
> task: ffffffff81c0e540 task.stack: ffffffff81c00000
> RIP: e030:[<ffffffff810013aa>] [<ffffffff810013aa>] xen_hypercall_sched_op+0xa/0x20
> RSP: e02b:ffffffff81c03e90 EFLAGS: 00000246
> RAX: 0000000000000000 RBX: ffffffff81c0e540 RCX: ffffffff810013aa
> RDX: ffffffff81c4ba70 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000007ff0 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: ffffffff81c0e540 R15: ffffffff81c0e540
> FS: 00007f977d3c2700(0000) GS:ffff8801f5a00000(0000) knlGS:0000000000000000
> CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055ae9becabc8 CR3: 00000001d6a40000 CR4: 0000000000002660
> Stack:
> 0000000000000001 0000000000000001 ffffffff8101b55c ffffffff81611ec8
> ffffffff81c0e540 0000000000000000 ffffffff810bc280 ffffffff81c0e540
> ffffffff81c0e540 ebeac214e330bd3f addce6dcadd009c9 ffffffffffffffff
> Call Trace:
> [<ffffffff8101b55c>] ? xen_safe_halt+0xc/0x20
> [<ffffffff81611ec8>] ? default_idle+0x18/0xd0
> [<ffffffff810bc280>] ? cpu_startup_entry+0x1f0/0x260
> [<ffffffff81d4bf84>] ? start_kernel+0x46d/0x48d
> [<ffffffff81d510e6>] ? xen_start_kernel+0x52e/0x538
> Code: cc 51 41 53 b8 1c 00 00 00 0f 05 41 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc


Looking at the dis-assembly of xen_clocksource_get_cycles() in
arch/x86/xen/time.c I see no path how that should call
__blk_mq_run_hw_queue():

> 00000000000001a0 <xen_clocksource_get_cycles> mov %gs:0x0(%rip),%rdi # 00000000000001a8 <xen_clocksource_get_cycles+0x8>
> 00000000000001a8 <xen_clocksource_get_cycles+0x8> add $0x20,%rdi
> ret = pvclock_clocksource_read(src);
> 00000000000001ac <xen_clocksource_get_cycles+0xc> callq 00000000000001b1 <xen_clocksource_get_cycles+0x11>
> }
>
> static cycle_t xen_clocksource_get_cycles(struct clocksource *cs)
> {
> return xen_clocksource_read();
> }
> 00000000000001b1 <xen_clocksource_get_cycles+0x11> retq
> 00000000000001b2 <xen_clocksource_get_cycles+0x12> data16 data16 data16 data16 nopw %cs:0x0(%rax,%rax,1)
>
> static void xen_read_wallclock(struct timespec *ts)
> {
> struct shared_info *s = HYPERVISOR_shared_info;
> struct pvclock_wall_clock *wall_clock = &(s->wc);
> 00000000000001c0 <xen_get_wallclock> mov 0x0(%rip),%rax # 00000000000001c7 <xen_get_wallclock+0x7>


Here's another dump, which diverges from xen_clocksource_get_cycles() to
some completely other function:

> INFO: task btrfs-transacti:522 blocked for more than 300 seconds.
> btrfs-transacti D 0 522 2 0x00000000
> ffff8801f3836000 0000000000000000 ffff8801f4a24f00 ffff8801f32da1c0
> ffff8801f5b18780 ffffc9004199fa40 ffffffff8160cd2d 0000000000000000
> ffff8801741a58a8 0000000000000102 000000000000000e ffff8801f32da1c0
> Call Trace:
> [<ffffffff8160cd2d>] ? __schedule+0x23d/0x6d0
> [<ffffffff8160da60>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160d1f2>] ? schedule+0x32/0x80
> [<ffffffff81610729>] ? schedule_timeout+0x249/0x300
***
> [<ffffffff8101b7d1>] ? xen_clocksource_get_cycles+0x11/0x20
> [<ffffffff8160da60>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160ca74>] ? io_schedule_timeout+0xb4/0x130
> [<ffffffff810bb5e7>] ? prepare_to_wait+0x57/0x80
> [<ffffffff8160da77>] ? bit_wait_io+0x17/0x60
> [<ffffffff8160d56c>] ? __wait_on_bit+0x5c/0x90
> [<ffffffff8117e18e>] ? find_get_pages_tag+0x15e/0x300
> [<ffffffff8117d016>] ? wait_on_page_bit+0x86/0xa0
> [<ffffffff810bb910>] ? autoremove_wake_function+0x40/0x40
> [<ffffffff8117d107>] ? __filemap_fdatawait_range+0xd7/0x150
> [<ffffffff8117d18f>] ? filemap_fdatawait_range+0xf/0x30
> [<ffffffffc0175643>] ? btrfs_wait_ordered_range+0x73/0x110 [btrfs]
> [<ffffffffc01a2a0d>] ? btrfs_wait_cache_io+0x5d/0x1f0 [btrfs]
> [<ffffffffc0141a36>] ? btrfs_write_dirty_block_groups+0x106/0x380 [btrfs]
> [<ffffffffc0140c5d>] ? btrfs_run_delayed_refs+0x1fd/0x2b0 [btrfs]
> [<ffffffffc01551d7>] ? commit_cowonly_roots+0x257/0x2f0 [btrfs]
> [<ffffffffc0157a24>] ? btrfs_commit_transaction+0x4e4/0xa40 [btrfs]
> [<ffffffffc015801d>] ? start_transaction+0x9d/0x4a0 [btrfs]
> [<ffffffffc01523a2>] ? transaction_kthread+0x1b2/0x1f0 [btrfs]
> [<ffffffffc01521f0>] ? btrfs_cleanup_transaction+0x580/0x580 [btrfs]
> [<ffffffff810975c0>] ? kthread+0xf0/0x110
> [<ffffffff8102476b>] ? __switch_to+0x2bb/0x700
> [<ffffffff810974d0>] ? kthread_park+0x60/0x60
> [<ffffffff81611d35>] ? ret_from_fork+0x25/0x30

And another one:
> INFO: task smbd:20101 blocked for more than 300 seconds.
> smbd D 0 20101 1714 0x00000000
> ffff8801f01cac00 0000000000000000 ffff8801f4a241c0 ffff88007f9a5240
> ffff8801f5b98780 ffffc90049a33bc0 ffffffff8160cd2d ffff8800f78bb5b0
> fd2236313fb5274b 000000008dc3c1a0 ffff8801f3ef0a40 ffff88007f9a5240
> Call Trace:
> [<ffffffff8160cd2d>] ? __schedule+0x23d/0x6d0
> [<ffffffff8160da60>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160d1f2>] ? schedule+0x32/0x80
> [<ffffffff81610729>] ? schedule_timeout+0x249/0x300
> [<ffffffff81336486>] ? __radix_tree_lookup+0x76/0xe0
***
> [<ffffffff8101b7d1>] ? xen_clocksource_get_cycles+0x11/0x20
> [<ffffffff8160da60>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160ca74>] ? io_schedule_timeout+0xb4/0x130
> [<ffffffff810bb5e7>] ? prepare_to_wait+0x57/0x80
> [<ffffffff8160da77>] ? bit_wait_io+0x17/0x60
> [<ffffffff8160d56c>] ? __wait_on_bit+0x5c/0x90
> [<ffffffffc00f290b>] ? __jbd2_journal_file_buffer+0xcb/0x180 [jbd2]
> [<ffffffff8160da60>] ? bit_wait_timeout+0x90/0x90
> [<ffffffff8160d6ce>] ? out_of_line_wait_on_bit+0x7e/0xa0
> [<ffffffff810bb910>] ? autoremove_wake_function+0x40/0x40
> [<ffffffffc00f2bc8>] ? do_get_write_access+0x208/0x420 [jbd2]
> [<ffffffffc00f2e0e>] ? jbd2_journal_get_write_access+0x2e/0x60 [jbd2]
> [<ffffffffc02c78a6>] ? __ext4_journal_get_write_access+0x36/0x70 [ext4]
> [<ffffffffc02a3913>] ? ext4_orphan_add+0xd3/0x230 [ext4]
> [<ffffffffc0296b4a>] ? ext4_mark_inode_dirty+0x6a/0x200 [ext4]
> [<ffffffffc02a4b8a>] ? ext4_unlink+0x36a/0x380 [ext4]
> [<ffffffff81211677>] ? vfs_unlink+0xe7/0x180
> [<ffffffff81214439>] ? do_unlinkat+0x289/0x300
> [<ffffffff81611abb>] ? system_call_fast_compare_end+0xc/0x9b

This does not look normal to me or did I miss something?

Where can I get more information on why there is no progress for 300s,
what should I do to debug which task is waiting for what?

The traces of the of other CPUs look normal to me: the one posted first
above is the shortest, in all other cases they were sooner or later
waiting for IO (my interpretation, but I can post them if necessary.)

This problem occurs since the upgrade of the Linux kernel inside the VM
from 4.1.x to 4.9.32 and now 4.9.52.

Any help is appreciated.
Philipp Hahn
--
Philipp Hahn
Open Source Software Engineer

Univention GmbH
be open.
Mary-Somerville-Str. 1
D-28359 Bremen
Tel.: +49 421 22232-0
Fax : +49 421 22232-99
hahn@univention.de

http://www.univention.de/
Geschäftsführer: Peter H. Ganten
HRB 20755 Amtsgericht Bremen
Steuer-Nr.: 71-597-02876

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