Hi, To quickly summarize, on a Xen domU instance with a disk structure of XFS on LVM2 on RAID10 on 8x virtual disks, all tasks performing I/O to said XFS partition hung and I cannot prove or disprove it to be dom0 issue. And now the long(er) version: On an Amazon EC2 (xen) instance, I had I/O to one of the EBS (Elastic Block Store virtual disk) devices block with iostat showing one single request pending. Kernel logs showed hung tasks so after grabbing those I reset the instance but - while I''m told that Amazon''s logs don''t show any problems with the EBS - Amazon want the opportunity to exclude an EBS problem by examining things from the dom0 side while the problem is occurring before delving into the kernel. So what I''m really hoping for is for somebody to take a look at the call stacks of the hung tasks and rule in/out a race condition. The kernel is linux-2.6.35.14-106.53.amzn1 but I''ve resolved the call stack to the source using gdb "list *(...)" as described in http://ds9a.nl/symoops.html. If it''s needed, I''ll send the relevant parts (or all of it) in a separate mail as it''ll make this one too big. I''m sending to xen-devel as I''d think XFS on LVM2 on RAID10 would be not so uncommon, so I''d say Xen has something to do with it if there is in fact a race condition. I think that covers everything. Thanks in advance to anybody who takes the time to glance at this. Please ensure my mail address is included in replies as I am not subscribed. Firstly, the hung task information: INFO: task md127_raid10:967 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. md127_raid10 D ffff88000ab98200 0 967 2 0x00000000 ffff880882801c40 0000000000000246 0000000000000000 0000000000014200 ffff880882801fd8 0000000000014200 ffff880882801fd8 ffff8808828b1690 0000000000014200 0000000000014200 ffff880882801fd8 0000000000014200 Call Trace: [<ffffffff8124f211>] md_super_wait+0xd1/0xf0 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffff8124f7c8>] md_update_sb+0x268/0x3e0 [<ffffffff813192b9>] ? _raw_spin_unlock_irqrestore+0x19/0x20 [<ffffffff81253cca>] md_check_recovery+0x21a/0x540 [<ffffffffa0014a57>] raid10d+0x47/0x920 [raid10] [<ffffffff81006f1d>] ? xen_force_evtchn_callback+0xd/0x10 [<ffffffff8100766f>] ? xen_restore_fl_direct_end+0x0/0x1 [<ffffffff813192b9>] ? _raw_spin_unlock_irqrestore+0x19/0x20 [<ffffffff8124ef56>] md_thread+0x116/0x150 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffff8124ee40>] ? md_thread+0x0/0x150 [<ffffffff8106816e>] kthread+0x8e/0xa0 [<ffffffff8100bc64>] kernel_thread_helper+0x4/0x10 [<ffffffff8100b063>] ? int_ret_from_sys_call+0x7/0x1b [<ffffffff8131975d>] ? retint_restore_args+0x5/0x6 [<ffffffff8100bc60>] ? kernel_thread_helper+0x0/0x10 INFO: task kdmflush:1004 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kdmflush D ffff88000abd0200 0 1004 2 0x00000000 ffff880882ff5d30 0000000000000246 0000000000000000 0000000000014200 ffff880882ff5fd8 0000000000014200 ffff880882ff5fd8 ffff8808828b43b0 0000000000014200 0000000000014200 ffff880882ff5fd8 0000000000014200 Call Trace: [<ffffffff8131738e>] io_schedule+0x6e/0xb0 [<ffffffffa0002052>] dm_wait_for_completion+0xc2/0x150 [dm_mod] [<ffffffff81049650>] ? default_wake_function+0x0/0x10 [<ffffffffa0002de0>] ? dm_wq_work+0x0/0x1d0 [dm_mod] [<ffffffffa0002d8e>] dm_flush+0x1e/0x70 [dm_mod] [<ffffffffa0002e22>] dm_wq_work+0x42/0x1d0 [dm_mod] [<ffffffffa0002de0>] ? dm_wq_work+0x0/0x1d0 [dm_mod] [<ffffffff81064130>] worker_thread+0x160/0x250 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffff81063fd0>] ? worker_thread+0x0/0x250 [<ffffffff8106816e>] kthread+0x8e/0xa0 [<ffffffff8100bc64>] kernel_thread_helper+0x4/0x10 [<ffffffff8100b063>] ? int_ret_from_sys_call+0x7/0x1b [<ffffffff8131975d>] ? retint_restore_args+0x5/0x6 [<ffffffff8100bc60>] ? kernel_thread_helper+0x0/0x10 INFO: task xfsbufd/dm-0:1470 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. xfsbufd/dm-0 D ffff88000abd0200 0 1470 2 0x00000000 ffff88088518fb70 0000000000000246 0000000000000000 0000000000014200 ffff88088518ffd8 0000000000014200 ffff88088518ffd8 ffff8808853b9690 0000000000014200 0000000000014200 ffff88088518ffd8 0000000000014200 Call Trace: [<ffffffff8124d95d>] md_write_start+0xad/0x1d0 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffffa00162b0>] make_request+0x70/0x530 [raid10] [<ffffffff8124dbc1>] md_make_request+0xc1/0x220 [<ffffffffa00030a1>] ? dm_request+0xf1/0x230 [dm_mod] [<ffffffff81198bf3>] generic_make_request+0x1f3/0x3c0 [<ffffffffa0001e26>] ? dm_get_live_table+0x46/0x60 [dm_mod] [<ffffffffa00032fc>] ? dm_merge_bvec+0xbc/0x140 [dm_mod] [<ffffffff81198e3f>] submit_bio+0x7f/0x110 [<ffffffffa0119abc>] _xfs_buf_ioapply+0x18c/0x2c0 [xfs] [<ffffffffa011ab51>] xfs_buf_iorequest+0x31/0x80 [xfs] [<ffffffffa011b96d>] xfs_bdstrat_cb+0x2d/0x50 [xfs] [<ffffffffa011afc2>] xfsbufd+0xe2/0x1a0 [xfs] [<ffffffffa011aee0>] ? xfsbufd+0x0/0x1a0 [xfs] [<ffffffff8106816e>] kthread+0x8e/0xa0 [<ffffffff8100bc64>] kernel_thread_helper+0x4/0x10 [<ffffffff8100b063>] ? int_ret_from_sys_call+0x7/0x1b [<ffffffff8131975d>] ? retint_restore_args+0x5/0x6 [<ffffffff8100bc60>] ? kernel_thread_helper+0x0/0x10 INFO: task mysqld:5207 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. mysqld D ffff88000abec200 0 5207 4991 0x00000000 ffff8808836098b8 0000000000000286 0000000000000000 0000000000014200 ffff880883609fd8 0000000000014200 ffff880883609fd8 ffff880883ae8000 0000000000014200 0000000000014200 ffff880883609fd8 0000000000014200 Call Trace: [<ffffffff813192b9>] ? _raw_spin_unlock_irqrestore+0x19/0x20 [<ffffffff8124d95d>] md_write_start+0xad/0x1d0 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffffa00162b0>] make_request+0x70/0x530 [raid10] [<ffffffff8124dbc1>] md_make_request+0xc1/0x220 [<ffffffff81006f1d>] ? xen_force_evtchn_callback+0xd/0x10 [<ffffffffa00030a1>] ? dm_request+0xf1/0x230 [dm_mod] [<ffffffff81006f1d>] ? xen_force_evtchn_callback+0xd/0x10 [<ffffffff81198bf3>] generic_make_request+0x1f3/0x3c0 [<ffffffffa0001e26>] ? dm_get_live_table+0x46/0x60 [dm_mod] [<ffffffffa0005aad>] ? linear_merge+0x4d/0x60 [dm_mod] [<ffffffffa00032fc>] ? dm_merge_bvec+0xbc/0x140 [dm_mod] [<ffffffff81198e3f>] submit_bio+0x7f/0x110 [<ffffffffa0117732>] xfs_submit_ioend_bio+0x52/0x90 [xfs] [<ffffffffa0117821>] xfs_submit_ioend+0xb1/0x110 [xfs] [<ffffffffa0118880>] xfs_page_state_convert+0x330/0x6a0 [xfs] [<ffffffffa0118d46>] xfs_vm_writepage+0x76/0x110 [xfs] [<ffffffff810bfc22>] __writepage+0x12/0x40 [<ffffffff810c0ccf>] write_cache_pages+0x1cf/0x3f0 [<ffffffff810bfc10>] ? __writepage+0x0/0x40 [<ffffffff81007521>] ? xen_clocksource_read+0x21/0x30 [<ffffffff810c0f0f>] generic_writepages+0x1f/0x30 [<ffffffffa0117cb8>] xfs_vm_writepages+0x58/0x70 [xfs] [<ffffffff810c0f3c>] do_writepages+0x1c/0x30 [<ffffffff810b8b83>] __filemap_fdatawrite_range+0x53/0x60 [<ffffffff810b8bea>] filemap_write_and_wait_range+0x5a/0x80 [<ffffffff8111c9b2>] vfs_fsync_range+0x52/0x90 [<ffffffff8111ca57>] vfs_fsync+0x17/0x20 [<ffffffff8111ca95>] do_fsync+0x35/0x60 [<ffffffff8111caeb>] sys_fsync+0xb/0x10 [<ffffffff8100ae42>] system_call_fastpath+0x16/0x1b INFO: task flush-253:0:14617 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. flush-253:0 D ffff88000abd0200 0 14617 2 0x00000000 ffff880882b07620 0000000000000246 0000000000000000 0000000000014200 ffff880882b07fd8 0000000000014200 ffff880882b07fd8 ffff8808055643b0 0000000000014200 0000000000014200 ffff880882b07fd8 0000000000014200 Call Trace: [<ffffffff8124d95d>] md_write_start+0xad/0x1d0 [<ffffffff81068630>] ? autoremove_wake_function+0x0/0x40 [<ffffffffa00162b0>] make_request+0x70/0x530 [raid10] [<ffffffff8124dbc1>] md_make_request+0xc1/0x220 [<ffffffff81006f1d>] ? xen_force_evtchn_callback+0xd/0x10 [<ffffffffa00030a1>] ? dm_request+0xf1/0x230 [dm_mod] [<ffffffff81006f1d>] ? xen_force_evtchn_callback+0xd/0x10 [<ffffffff81198bf3>] generic_make_request+0x1f3/0x3c0 [<ffffffff81007521>] ? xen_clocksource_read+0x21/0x30 [<ffffffff81198e3f>] submit_bio+0x7f/0x110 [<ffffffff811189a2>] ? __mark_inode_dirty+0x92/0x170 [<ffffffffa0117732>] xfs_submit_ioend_bio+0x52/0x90 [xfs] [<ffffffffa0117866>] xfs_submit_ioend+0xf6/0x110 [xfs] [<ffffffffa0118880>] xfs_page_state_convert+0x330/0x6a0 [xfs] [<ffffffffa0118d46>] xfs_vm_writepage+0x76/0x110 [xfs] [<ffffffff810bfc22>] __writepage+0x12/0x40 [<ffffffff810c0ccf>] write_cache_pages+0x1cf/0x3f0 [<ffffffff810bfc10>] ? __writepage+0x0/0x40 [<ffffffff810c0f0f>] generic_writepages+0x1f/0x30 [<ffffffffa0117cb8>] xfs_vm_writepages+0x58/0x70 [xfs] [<ffffffff810c0f3c>] do_writepages+0x1c/0x30 [<ffffffff81117c5a>] writeback_single_inode+0xea/0x3f0 [<ffffffff811183ad>] writeback_sb_inodes+0x18d/0x270 [<ffffffff81007521>] ? xen_clocksource_read+0x21/0x30 [<ffffffff81118c94>] writeback_inodes_wb+0xa4/0x1b0 [<ffffffff81118feb>] wb_writeback+0x24b/0x2b0 [<ffffffff8102e568>] ? pvclock_clocksource_read+0x58/0xd0 [<ffffffff810084f5>] ? xen_spin_lock+0xa5/0x110 [<ffffffff811191af>] wb_do_writeback+0x15f/0x170 [<ffffffff8105c6a0>] ? process_timeout+0x0/0x10 [<ffffffff8111920f>] bdi_writeback_task+0x4f/0x160 [<ffffffff81068512>] ? bit_waitqueue+0x12/0xc0 [<ffffffff810cda21>] bdi_start_fn+0x81/0x100 [<ffffffff810cd9a0>] ? bdi_start_fn+0x0/0x100 [<ffffffff8106816e>] kthread+0x8e/0xa0 [<ffffffff8100bc64>] kernel_thread_helper+0x4/0x10 [<ffffffff8100b063>] ? int_ret_from_sys_call+0x7/0x1b [<ffffffff8131975d>] ? retint_restore_args+0x5/0x6 [<ffffffff8100bc60>] ? kernel_thread_helper+0x0/0x10 And then dmesg output: [ 0.000000] Initializing cgroup subsys cpuset [ 0.000000] Initializing cgroup subsys cpu [ 0.000000] Linux version 2.6.35.14-106.53.amzn1.x86_64 (mockbuild@build-31006.build) (gcc version 4.4.5 20110214 (Red Hat 4.4.5-6) (GCC) ) #1 SMP Fri Jan 6 16:20:10 UTC 2012 [ 0.000000] Command line: root=LABEL=/ console=hvc0 LANG=en_US.UTF-8 KEYTABLE=us [ 0.000000] Marking TSC unstable due to Xen domain [ 0.000000] ACPI in unprivileged domain disabled [ 0.000000] released 0 pages of unused memory [ 0.000000] BIOS-provided physical RAM map: [ 0.000000] Xen: 0000000000000000 - 00000000000a0000 (usable) [ 0.000000] Xen: 00000000000a0000 - 0000000000100000 (reserved) [ 0.000000] Xen: 0000000000100000 - 000000088b800000 (usable) [ 0.000000] NX (Execute Disable) protection: active [ 0.000000] DMI not present or invalid. [ 0.000000] e820 update range: 0000000000000000 - 0000000000001000 (usable) ==> (reserved) [ 0.000000] e820 remove range: 00000000000a0000 - 0000000000100000 (usable) [ 0.000000] No AGP bridge found [ 0.000000] last_pfn = 0x88b800 max_arch_pfn = 0x400000000 [ 0.000000] last_pfn = 0x100000 max_arch_pfn = 0x400000000 [ 0.000000] initial memory mapped : 0 - 20000000 [ 0.000000] init_memory_mapping: 0000000000000000-0000000100000000 [ 0.000000] 0000000000 - 0100000000 page 4k [ 0.000000] kernel direct mapping tables up to 100000000 @ 100000-905000 [ 0.000000] init_memory_mapping: 0000000100000000-000000088b800000 [ 0.000000] 0100000000 - 088b800000 page 4k [ 0.000000] kernel direct mapping tables up to 88b800000 @ 6ed9000-b359000 [ 0.000000] RAMDISK: 0185a000 - 02a3f000 [ 0.000000] No NUMA configuration found [ 0.000000] Faking a node at 0000000000000000-000000088b800000 [ 0.000000] Initmem setup node 0 0000000000000000-000000088b800000 [ 0.000000] NODE_DATA [0000000100000000 - 0000000100004fff] [ 0.000000] early_res array is doubled to 64 at [7000 - 77ff] [ 0.000000] early_res array is doubled to 128 at [7800 - 87ff] [ 0.000000] early_res array is doubled to 256 at [8800 - a7ff] [ 0.000000] early_res array is doubled to 512 at [a800 - e7ff] [ 0.000000] Zone PFN ranges: [ 0.000000] DMA 0x00000001 -> 0x00001000 [ 0.000000] DMA32 0x00001000 -> 0x00100000 [ 0.000000] Normal 0x00100000 -> 0x0088b800 [ 0.000000] Movable zone start PFN for each node [ 0.000000] early_node_map[2] active PFN ranges [ 0.000000] 0: 0x00000001 -> 0x000000a0 [ 0.000000] 0: 0x00000100 -> 0x0088b800 [ 0.000000] On node 0 totalpages: 8959903 [ 0.000000] DMA zone: 56 pages used for memmap [ 0.000000] DMA zone: 0 pages reserved [ 0.000000] DMA zone: 3943 pages, LIFO batch:0 [ 0.000000] DMA32 zone: 14280 pages used for memmap [ 0.000000] DMA32 zone: 1030200 pages, LIFO batch:31 [ 0.000000] Normal zone: 108164 pages used for memmap [ 0.000000] Normal zone: 7803260 pages, LIFO batch:31 [ 0.000000] SMP: Allowing 4 CPUs, 0 hotplug CPUs [ 0.000000] No local APIC present [ 0.000000] APIC: disable apic facility [ 0.000000] APIC: switched to apic NOOP [ 0.000000] nr_irqs_gsi: 16 [ 0.000000] PCI: Warning: Cannot find a gap in the 32bit address range [ 0.000000] PCI: Unassigned devices with 32bit resource registers may break! [ 0.000000] Allocating PCI resources starting at 88b900000 (gap: 88b900000:400000) [ 0.000000] Booting paravirtualized kernel on Xen [ 0.000000] Xen version: 3.4.3-2.6.18 (preserve-AD) [ 0.000000] setup_percpu: NR_CPUS:32 nr_cpumask_bits:32 nr_cpu_ids:4 nr_node_ids:1 [ 0.000000] PERCPU: Embedded 28 pages/cpu @ffff88000ab84000 s85568 r8192 d20928 u114688 [ 0.000000] pcpu-alloc: s85568 r8192 d20928 u114688 alloc=28*4096 [ 0.000000] pcpu-alloc: [0] 0 [0] 1 [0] 2 [0] 3 [ 0.000000] trying to map vcpu_info 0 at ffff88000ab8f020, mfn e1df7f, offset 32 [ 0.000000] cpu 0 using vcpu_info at ffff88000ab8f020 [ 0.000000] trying to map vcpu_info 1 at ffff88000abab020, mfn e1df63, offset 32 [ 0.000000] cpu 1 using vcpu_info at ffff88000abab020 [ 0.000000] trying to map vcpu_info 2 at ffff88000abc7020, mfn e1df47, offset 32 [ 0.000000] cpu 2 using vcpu_info at ffff88000abc7020 [ 0.000000] trying to map vcpu_info 3 at ffff88000abe3020, mfn e1df2b, offset 32 [ 0.000000] cpu 3 using vcpu_info at ffff88000abe3020 [ 0.000000] Xen: using vcpu_info placement [ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 8837403 [ 0.000000] Policy zone: Normal [ 0.000000] Kernel command line: root=LABEL=/ console=hvc0 LANG=en_US.UTF-8 KEYTABLE=us [ 0.000000] PID hash table entries: 4096 (order: 3, 32768 bytes) [ 0.000000] Checking aperture... [ 0.000000] No AGP bridge found [ 0.000000] Subtract (281 early reservations) [ 0.000000] #1 [0006e9e000 - 0006ed9000] XEN PAGETABLES [ 0.000000] #2 [0001000000 - 00018389d0] TEXT DATA BSS [ 0.000000] #3 [000185a000 - 0002a3f000] RAMDISK [ 0.000000] #4 [0002a3f000 - 0006e9e000] XEN START INFO [ 0.000000] #5 [0000001000 - 0000003000] TRAMPOLINE [ 0.000000] #6 [0000003000 - 0000007000] ACPI WAKEUP [ 0.000000] #7 [0000100000 - 00008c7000] PGTABLE [ 0.000000] #8 [0006ed9000 - 000ab54000] PGTABLE [ 0.000000] #9 [0100000000 - 0100005000] NODE_DATA [ 0.000000] #10 [0001838a00 - 0001839a00] BOOTMEM [ 0.000000] #11 [0001839a00 - 000183aa00] BOOTMEM [ 0.000000] #12 [000183aa00 - 000183bb20] BOOTMEM [ 0.000000] #13 [0100005000 - 0100006000] BOOTMEM [ 0.000000] #14 [0100006000 - 0100007000] BOOTMEM [ 0.000000] #15 [0100007000 - 0100008000] BOOTMEM [ 0.000000] #16 [0100008000 - 0100009000] BOOTMEM [ 0.000000] #17 [0100009000 - 010000a000] BOOTMEM [ 0.000000] #18 [010000a000 - 010000b000] BOOTMEM [ 0.000000] #19 [010000b000 - 010000c000] BOOTMEM [ 0.000000] #20 [010000c000 - 010000d000] BOOTMEM [ 0.000000] #21 [010000d000 - 010000e000] BOOTMEM [ 0.000000] #22 [010000e000 - 010000f000] BOOTMEM [ 0.000000] #23 [010000f000 - 0100010000] BOOTMEM [ 0.000000] #24 [0100010000 - 0100011000] BOOTMEM [ 0.000000] #25 [0100011000 - 0100012000] BOOTMEM [ 0.000000] #26 [0100012000 - 0100013000] BOOTMEM [ 0.000000] #27 [0100013000 - 0100014000] BOOTMEM [ 0.000000] #28 [0100014000 - 0100015000] BOOTMEM [ 0.000000] #29 [0100015000 - 0100016000] BOOTMEM [ 0.000000] #30 [0100016000 - 0100017000] BOOTMEM [ 0.000000] #31 [0100017000 - 0100018000] BOOTMEM [ 0.000000] #32 [0100018000 - 0100019000] BOOTMEM [ 0.000000] #33 [0100019000 - 010001a000] BOOTMEM [ 0.000000] #34 [010001a000 - 010001b000] BOOTMEM [ 0.000000] #35 [010001b000 - 010001c000] BOOTMEM [ 0.000000] #36 [010001c000 - 010001d000] BOOTMEM [ 0.000000] #37 [010001d000 - 010001e000] BOOTMEM [ 0.000000] #38 [010001e000 - 010001f000] BOOTMEM [ 0.000000] #39 [010001f000 - 0100020000] BOOTMEM [ 0.000000] #40 [0100020000 - 0100021000] BOOTMEM [ 0.000000] #41 [0100021000 - 0100022000] BOOTMEM [ 0.000000] #42 [0100022000 - 0100023000] BOOTMEM [ 0.000000] #43 [0100023000 - 0100024000] BOOTMEM [ 0.000000] #44 [0100024000 - 0100025000] BOOTMEM [ 0.000000] #45 [0100025000 - 0100026000] BOOTMEM [ 0.000000] #46 [0100026000 - 0100027000] BOOTMEM [ 0.000000] #47 [0100027000 - 0100028000] BOOTMEM [ 0.000000] #48 [0100028000 - 0100029000] BOOTMEM [ 0.000000] #49 [0100029000 - 010002a000] BOOTMEM [ 0.000000] #50 [010002a000 - 010002b000] BOOTMEM [ 0.000000] #51 [010002b000 - 010002c000] BOOTMEM [ 0.000000] #52 [010002c000 - 010002d000] BOOTMEM [ 0.000000] #53 [010002d000 - 010002e000] BOOTMEM [ 0.000000] #54 [010002e000 - 010002f000] BOOTMEM [ 0.000000] #55 [010002f000 - 0100030000] BOOTMEM [ 0.000000] #56 [0100030000 - 0100031000] BOOTMEM [ 0.000000] #57 [0100031000 - 0100032000] BOOTMEM [ 0.000000] #58 [0100032000 - 0100033000] BOOTMEM [ 0.000000] #59 [0100033000 - 0100034000] BOOTMEM [ 0.000000] #60 [0100034000 - 0100035000] BOOTMEM [ 0.000000] #61 [0100035000 - 0100036000] BOOTMEM [ 0.000000] #62 [0100036000 - 0100037000] BOOTMEM [ 0.000000] #63 [0100037000 - 0100038000] BOOTMEM [ 0.000000] #64 [0100038000 - 0100039000] BOOTMEM [ 0.000000] #65 [0100039000 - 010003a000] BOOTMEM [ 0.000000] #66 [010003a000 - 010003b000] BOOTMEM [ 0.000000] #67 [010003b000 - 010003c000] BOOTMEM [ 0.000000] #68 [010003c000 - 010003d000] BOOTMEM [ 0.000000] #69 [010003d000 - 010003e000] BOOTMEM [ 0.000000] #70 [010003e000 - 010003f000] BOOTMEM [ 0.000000] #71 [010003f000 - 0100040000] BOOTMEM [ 0.000000] #72 [0100040000 - 0100041000] BOOTMEM [ 0.000000] #73 [0100041000 - 0100042000] BOOTMEM [ 0.000000] #74 [0100042000 - 0100043000] BOOTMEM [ 0.000000] #75 [0100043000 - 0100044000] BOOTMEM [ 0.000000] #76 [0100044000 - 0100045000] BOOTMEM [ 0.000000] #77 [0100045000 - 0100046000] BOOTMEM [ 0.000000] #78 [0100046000 - 0100047000] BOOTMEM [ 0.000000] #79 [0100047000 - 0100048000] BOOTMEM [ 0.000000] #80 [0100048000 - 0100049000] BOOTMEM [ 0.000000] #81 [0100049000 - 010004a000] BOOTMEM [ 0.000000] #82 [010004a000 - 010004b000] BOOTMEM [ 0.000000] #83 [010004b000 - 010004c000] BOOTMEM [ 0.000000] #84 [010004c000 - 010004d000] BOOTMEM [ 0.000000] #85 [010004d000 - 010004e000] BOOTMEM [ 0.000000] #86 [010004e000 - 010004f000] BOOTMEM [ 0.000000] #87 [010004f000 - 0100050000] BOOTMEM [ 0.000000] #88 [0100050000 - 0100051000] BOOTMEM [ 0.000000] #89 [0100051000 - 0100052000] BOOTMEM [ 0.000000] #90 [0100052000 - 0100053000] BOOTMEM [ 0.000000] #91 [0100053000 - 0100054000] BOOTMEM [ 0.000000] #92 [0100054000 - 0100055000] BOOTMEM [ 0.000000] #93 [0100055000 - 0100056000] BOOTMEM [ 0.000000] #94 [0100056000 - 0100057000] BOOTMEM [ 0.000000] #95 [0100057000 - 0100058000] BOOTMEM [ 0.000000] #96 [0100058000 - 0100059000] BOOTMEM [ 0.000000] #97 [0100059000 - 010005a000] BOOTMEM [ 0.000000] #98 [010005a000 - 010005b000] BOOTMEM [ 0.000000] #99 [010005b000 - 010005c000] BOOTMEM [ 0.000000] #100 [010005c000 - 010005d000] BOOTMEM [ 0.000000] #101 [010005d000 - 010005e000] BOOTMEM [ 0.000000] #102 [010005e000 - 010005f000] BOOTMEM [ 0.000000] #103 [010005f000 - 0100060000] BOOTMEM [ 0.000000] #104 [0100060000 - 0100061000] BOOTMEM [ 0.000000] #105 [0100061000 - 0100062000] BOOTMEM [ 0.000000] #106 [0100062000 - 0100063000] BOOTMEM [ 0.000000] #107 [0100063000 - 0100064000] BOOTMEM [ 0.000000] #108 [0100064000 - 0100065000] BOOTMEM [ 0.000000] #109 [0100065000 - 0100066000] BOOTMEM [ 0.000000] #110 [0100066000 - 0100067000] BOOTMEM [ 0.000000] #111 [0100067000 - 0100068000] BOOTMEM [ 0.000000] #112 [0100068000 - 0100069000] BOOTMEM [ 0.000000] #113 [0100069000 - 010006a000] BOOTMEM [ 0.000000] #114 [010006a000 - 010006b000] BOOTMEM [ 0.000000] #115 [010006b000 - 010006c000] BOOTMEM [ 0.000000] #116 [010006c000 - 010006d000] BOOTMEM [ 0.000000] #117 [010006d000 - 010006e000] BOOTMEM [ 0.000000] #118 [010006e000 - 010006f000] BOOTMEM [ 0.000000] #119 [010006f000 - 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01000d4000] BOOTMEM [ 0.000000] #220 [01000d4000 - 01000d5000] BOOTMEM [ 0.000000] #221 [01000d5000 - 01000d6000] BOOTMEM [ 0.000000] #222 [01000d6000 - 01000d7000] BOOTMEM [ 0.000000] #223 [01000d7000 - 01000d8000] BOOTMEM [ 0.000000] #224 [01000d8000 - 01000d9000] BOOTMEM [ 0.000000] #225 [01000d9000 - 01000da000] BOOTMEM [ 0.000000] #226 [01000da000 - 01000db000] BOOTMEM [ 0.000000] #227 [01000db000 - 01000dc000] BOOTMEM [ 0.000000] #228 [01000dc000 - 01000dd000] BOOTMEM [ 0.000000] #229 [01000dd000 - 01000de000] BOOTMEM [ 0.000000] #230 [01000de000 - 01000df000] BOOTMEM [ 0.000000] #231 [01000df000 - 01000e0000] BOOTMEM [ 0.000000] #232 [01000e0000 - 01000e1000] BOOTMEM [ 0.000000] #233 [01000e1000 - 01000e2000] BOOTMEM [ 0.000000] #234 [01000e2000 - 01000e3000] BOOTMEM [ 0.000000] #235 [01000e3000 - 01000e4000] BOOTMEM [ 0.000000] #236 [01000e4000 - 01000e5000] BOOTMEM [ 0.000000] #237 [01000e5000 - 01000e6000] BOOTMEM [ 0.000000] #238 [01000e6000 - 01000e7000] BOOTMEM [ 0.000000] #239 [01000e7000 - 01000e8000] BOOTMEM [ 0.000000] #240 [01000e8000 - 01000e9000] BOOTMEM [ 0.000000] #241 [01000e9000 - 01000ea000] BOOTMEM [ 0.000000] #242 [01000ea000 - 01000eb000] BOOTMEM [ 0.000000] #243 [01000eb000 - 01000ec000] BOOTMEM [ 0.000000] #244 [01000ec000 - 01000ed000] BOOTMEM [ 0.000000] #245 [01000ed000 - 01000ee000] BOOTMEM [ 0.000000] #246 [01000ee000 - 01000ef000] BOOTMEM [ 0.000000] #247 [01000ef000 - 01000f0000] BOOTMEM [ 0.000000] #248 [01000f0000 - 01000f1000] BOOTMEM [ 0.000000] #249 [01000f1000 - 01000f2000] BOOTMEM [ 0.000000] #250 [01000f2000 - 01000f3000] BOOTMEM [ 0.000000] #251 [01000f3000 - 01000f4000] BOOTMEM [ 0.000000] #252 [01000f4000 - 01000f5000] BOOTMEM [ 0.000000] #253 [01000f5000 - 01000f6000] BOOTMEM [ 0.000000] #254 [01000f6000 - 01000f7000] BOOTMEM [ 0.000000] #255 [0100200000 - 011e180000] MEMMAP 0 [ 0.000000] #256 [000183bb40 - 0001853b40] BOOTMEM [ 0.000000] #257 [000ab54000 - 000ab6c000] BOOTMEM [ 0.000000] #258 [000ab6c000 - 000ab84000] BOOTMEM [ 0.000000] #259 [0001854000 - 0001855000] BOOTMEM [ 0.000000] #260 [0001855000 - 0001856000] BOOTMEM [ 0.000000] #261 [0001856000 - 0001857000] BOOTMEM [ 0.000000] #262 [0001853b40 - 0001853c20] BOOTMEM [ 0.000000] #263 [0001853c40 - 0001853ca8] BOOTMEM [ 0.000000] #264 [0001853cc0 - 0001853d28] BOOTMEM [ 0.000000] #265 [0001853d40 - 0001853da8] BOOTMEM [ 0.000000] #266 [0001853dc0 - 0001853df7] BOOTMEM [ 0.000000] #267 [0001853e00 - 0001853e37] BOOTMEM [ 0.000000] #268 [000ab84000 - 000abf4000] BOOTMEM [ 0.000000] #269 [0001853e40 - 0001853e48] BOOTMEM [ 0.000000] #270 [0001853e80 - 0001853e88] BOOTMEM [ 0.000000] #271 [0001853ec0 - 0001853ed0] BOOTMEM [ 0.000000] #272 [0001853f00 - 0001853f20] BOOTMEM [ 0.000000] #273 [0001859000 - 0001859100] BOOTMEM [ 0.000000] #274 [0001853f40 - 0001853f88] BOOTMEM [ 0.000000] #275 [0001859100 - 0001859148] BOOTMEM [ 0.000000] #276 [000abf4000 - 000abfc000] BOOTMEM [ 0.000000] #277 [000abfc000 - 000ebfc000] BOOTMEM [ 0.000000] #278 [000ebfc000 - 000ec1c000] BOOTMEM [ 0.000000] #279 [000ec1c000 - 000ec5c000] BOOTMEM [ 0.000000] #280 [000000e800 - 0000016800] BOOTMEM [ 0.000000] Memory: 35113952k/35840000k available (3206k kernel code, 388k absent, 725660k reserved, 3713k data, 500k init) [ 0.000000] SLUB: Genslabs=14, HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1 [ 0.000000] Hierarchical RCU implementation. [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 0.000000] RCU-based detection of stalled CPUs is disabled. [ 0.000000] Verbose stalled-CPUs detection is disabled. [ 0.000000] NR_IRQS:4352 nr_irqs:304 [ 0.000000] Console: colour dummy device 80x25 [ 0.000000] console [tty0] enabled [ 0.000000] console [hvc0] enabled [ 0.000000] Xen: using vcpuop timer interface [ 0.000000] installing Xen timer for CPU 0 [ 0.000000] Detected 2666.760 MHz processor. [ 0.000999] Calibrating delay loop (skipped), value calculated using timer frequency.. 5333.52 BogoMIPS (lpj=2666760) [ 0.000999] pid_max: default: 32768 minimum: 301 [ 0.000999] Security Framework initialized [ 0.000999] SELinux: Disabled at boot. [ 0.005404] Dentry cache hash table entries: 8388608 (order: 14, 67108864 bytes) [ 0.020712] Inode-cache hash table entries: 4194304 (order: 13, 33554432 bytes) [ 0.028351] Mount-cache hash table entries: 256 [ 0.028548] Initializing cgroup subsys ns [ 0.028556] Initializing cgroup subsys cpuacct [ 0.028564] Initializing cgroup subsys devices [ 0.028571] Initializing cgroup subsys freezer [ 0.028618] CPU: Unsupported number of siblings 16 [ 0.028624] Performance Events: unsupported p6 CPU model 26 no PMU driver, software events only. [ 0.028704] SMP alternatives: switching to UP code [ 0.029073] cpu 0 spinlock event irq 1 [ 0.029261] installing Xen timer for CPU 1 [ 0.029274] cpu 1 spinlock event irq 7 [ 0.029299] SMP alternatives: switching to SMP code [ 0.000999] CPU: Unsupported number of siblings 16 [ 0.030203] installing Xen timer for CPU 2 [ 0.030224] cpu 2 spinlock event irq 13 [ 0.030254] alloc irq_desc for 16 on node 0 [ 0.030257] alloc kstat_irqs on node 0 [ 0.030264] alloc irq_desc for 17 on node 0 [ 0.030267] alloc kstat_irqs on node 0 [ 0.000999] CPU: Unsupported number of siblings 16 [ 0.030449] installing Xen timer for CPU 3 [ 0.030459] alloc irq_desc for 18 on node 0 [ 0.030462] alloc kstat_irqs on node 0 [ 0.030468] alloc irq_desc for 19 on node 0 [ 0.030471] alloc kstat_irqs on node 0 [ 0.030477] cpu 3 spinlock event irq 19 [ 0.030496] alloc irq_desc for 20 on node 0 [ 0.030498] alloc kstat_irqs on node 0 [ 0.030505] alloc irq_desc for 21 on node 0 [ 0.030507] alloc kstat_irqs on node 0 [ 0.030514] alloc irq_desc for 22 on node 0 [ 0.030516] alloc kstat_irqs on node 0 [ 0.030522] alloc irq_desc for 23 on node 0 [ 0.030524] alloc kstat_irqs on node 0 [ 0.000999] CPU: Unsupported number of siblings 16 [ 0.030604] Brought up 4 CPUs [ 0.030612] sizeof(vma)=184 bytes [ 0.030614] sizeof(page)=56 bytes [ 0.030617] sizeof(inode)=616 bytes [ 0.030619] sizeof(dentry)=192 bytes [ 0.030622] sizeof(ext3inode)=832 bytes [ 0.030625] sizeof(buffer_head)=104 bytes [ 0.030627] sizeof(skbuff)=232 bytes [ 0.030630] sizeof(task_struct)=5776 bytes [ 0.030705] devtmpfs: initialized [ 0.049732] Grant table initialized [ 0.049732] NET: Registered protocol family 16 [ 0.050023] alloc irq_desc for 24 on node 0 [ 0.050023] alloc kstat_irqs on node 0 [ 0.050055] PCI: Fatal: No config space access function found [ 0.056041] bio: create slab <bio-0> at 0 [ 0.056056] ACPI: Interpreter disabled. [ 0.056056] xen_balloon: Initialising balloon driver. [ 0.057206] vgaarb: loaded [ 0.057206] PCI: System does not support PCI [ 0.057206] PCI: System does not support PCI [ 0.058024] NetLabel: Initializing [ 0.058028] NetLabel: domain hash size = 128 [ 0.058032] NetLabel: protocols = UNLABELED CIPSOv4 [ 0.058050] NetLabel: unlabeled traffic allowed by default [ 0.058231] Switching to clocksource xen [ 0.058242] pnp: PnP ACPI: disabled [ 0.064983] NET: Registered protocol family 2 [ 0.065724] IP route cache hash table entries: 524288 (order: 10, 4194304 bytes) [ 0.067725] TCP established hash table entries: 524288 (order: 11, 8388608 bytes) [ 0.069338] TCP bind hash table entries: 65536 (order: 8, 1048576 bytes) [ 0.069527] TCP: Hash tables configured (established 524288 bind 65536) [ 0.069534] TCP reno registered [ 0.069735] UDP hash table entries: 32768 (order: 8, 1048576 bytes) [ 0.070086] UDP-Lite hash table entries: 32768 (order: 8, 1048576 bytes) [ 0.070377] NET: Registered protocol family 1 [ 0.070391] PCI: CLS 0 bytes, default 64 [ 0.070452] Unpacking initramfs... [ 0.093561] Freeing initrd memory: 18324k freed [ 0.098828] PCI-DMA: Using software bounce buffering for IO (SWIOTLB) [ 0.098844] Placing 64MB software IO TLB between ffff88000abfc000 - ffff88000ebfc000 [ 0.098850] software IO TLB at phys 0xabfc000 - 0xebfc000 [ 0.099483] platform rtc_cmos: registered platform RTC device (no PNP device found) [ 0.102533] audit: initializing netlink socket (disabled) [ 0.102554] type=2000 audit(1338184539.000:1): initialized [ 0.119492] VFS: Disk quotas dquot_6.5.2 [ 0.119601] Dquot-cache hash table entries: 512 (order 0, 4096 bytes) [ 0.119671] msgmni has been set to 32768 [ 0.120289] alg: No test for stdrng (krng) [ 0.120461] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254) [ 0.121449] io scheduler noop registered (default) [ 0.153417] alloc irq_desc for 25 on node 0 [ 0.153420] alloc kstat_irqs on node 0 [ 0.154172] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled [ 0.156832] loop: module loaded [ 0.157217] alloc irq_desc for 26 on node 0 [ 0.157221] alloc kstat_irqs on node 0 [ 0.158591] alloc irq_desc for 27 on node 0 [ 0.158594] alloc kstat_irqs on node 0 [ 0.160859] alloc irq_desc for 28 on node 0 [ 0.160862] alloc kstat_irqs on node 0 [ 0.164045] alloc irq_desc for 29 on node 0 [ 0.164049] alloc kstat_irqs on node 0 [ 0.167433] alloc irq_desc for 30 on node 0 [ 0.167437] alloc kstat_irqs on node 0 [ 0.170735] alloc irq_desc for 31 on node 0 [ 0.170738] alloc kstat_irqs on node 0 [ 0.175135] alloc irq_desc for 32 on node 0 [ 0.175139] alloc kstat_irqs on node 0 [ 0.178564] alloc irq_desc for 33 on node 0 [ 0.178569] alloc kstat_irqs on node 0 [ 0.182198] alloc irq_desc for 34 on node 0 [ 0.182203] alloc kstat_irqs on node 0 [ 0.184058] Initialising Xen virtual ethernet driver. [ 0.185857] blkfront: regular deviceid=0x801 major,minor=8,1, assuming parts/disk=16 [ 0.188580] blkfront: regular deviceid=0x855 major,minor=8,85, assuming parts/disk=16 [ 0.189479] PNP: No PS/2 controller found. Probing ports directly. [ 0.190535] mice: PS/2 mouse device common for all mice [ 0.190634] cpuidle: using governor ladder [ 0.190640] cpuidle: using governor menu [ 0.190715] TCP cubic registered [ 0.190722] NET: Registered protocol family 17 [ 0.190842] blkfront: regular deviceid=0x856 major,minor=8,86, assuming parts/disk=16 [ 0.191095] registered taskstats version 1 [ 0.191761] blkfront: regular deviceid=0x857 major,minor=8,87, assuming parts/disk=16 [ 0.192561] blkfront: regular deviceid=0x858 major,minor=8,88, assuming parts/disk=16 [ 0.193397] blkfront: regular deviceid=0x851 major,minor=8,81, assuming parts/disk=16 [ 0.194274] blkfront: regular deviceid=0x852 major,minor=8,82, assuming parts/disk=16 [ 0.195039] blkfront: regular deviceid=0x853 major,minor=8,83, assuming parts/disk=16 [ 0.195888] blkfront: regular deviceid=0x854 major,minor=8,84, assuming parts/disk=16 [ 0.196588] alloc irq_desc for 35 on node 0 [ 0.196591] alloc kstat_irqs on node 0 [ 0.291074] XENBUS: Device with no driver: device/console/0 [ 0.291315] Freeing unused kernel memory: 500k freed [ 0.291457] Write protecting the kernel read-only data: 6144k [ 0.294260] Freeing unused kernel memory: 872k freed [ 0.294770] Freeing unused kernel memory: 772k freed [ 0.338850] device-mapper: uevent: version 1.0.3 [ 0.339070] device-mapper: ioctl: 4.19.1-ioctl (2010-10-12) initialised: dm-devel@redhat.com [ 0.347400] udev: starting version 147 [ 0.464874] md: bind<xvdf8> [ 0.474746] md: bind<xvdf7> [ 0.482043] md: bind<xvdf4> [ 0.540137] md: bind<xvdf3> [ 0.548545] md: bind<xvdf5> [ 0.558959] md: bind<xvdf2> [ 0.590210] md: bind<xvdf6> [ 0.605807] md: bind<xvdf1> [ 0.617615] md: raid10 personality registered for level 10 [ 0.617973] md/raid10:md127: active with 8 out of 8 devices [ 0.618052] md127: detected capacity change from 0 to 42944430080 [ 0.619764] md127: unknown partition table [ 0.853476] dracut: Scanning devices md127 for LVM volume groups [ 0.952821] dracut: Reading all physical volumes. This may take a while... [ 0.952917] dracut: Found volume group "lvm" using metadata type lvm2 [ 1.001982] dracut: /dev/mapper/lvm-mysql not set up by udev: Falling back to direct node creation. [ 1.002490] dracut: The link /dev/lvm/mysql should had been created by udev but it was not found. Falling back to direct link creation. [ 1.002901] dracut: 1 logical volume(s) in volume group "lvm" now active [ 1.009194] dracut: Assembling MD RAID arrays [ 1.522720] EXT4-fs (xvda1): mounted filesystem with ordered data mode. Opts: (null) [ 1.714045] dracut: Remounting /dev/disk/by-label/\x2f with -o noatime,ro [ 1.724168] EXT4-fs (xvda1): mounted filesystem with ordered data mode. Opts: (null) [ 1.731079] dracut: Mounted root filesystem /dev/xvda1 [ 2.074312] dracut: Loading SELinux policy [ 4.435236] dracut: /sbin/load_policy: Can''t load policy: No such device [ 4.497683] dracut: Switching root [ 7.536918] usbcore: registered new interface driver usbfs [ 7.537147] usbcore: registered new interface driver hub [ 7.537356] usbcore: registered new device driver usb [ 9.689524] udev: starting version 147 [ 10.573499] rtc_cmos: probe of rtc_cmos failed with error -16 [ 15.475706] EXT4-fs (xvda1): re-mounted. Opts: (null) [ 15.887250] SGI XFS with ACLs, security attributes, realtime, large block/inode numbers, no debug enabled [ 15.889278] SGI XFS Quota Management subsystem [ 15.893832] XFS mounting filesystem dm-0 [ 16.415440] Ending clean XFS mount for filesystem: dm-0 [ 16.927608] Adding 1048572k swap on /.swapfile. Priority:-1 extents:4 across:1073148k SS -- Regards, Jason Stubbs
Dave Chinner
2012-Jun-12 03:57 UTC
Re: PROBLEM: Possible race between xen, md, dm and/or xfs
On Fri, Jun 08, 2012 at 03:45:46PM +1000, Jason Stubbs wrote:> Hi, > > To quickly summarize, on a Xen domU instance with a disk structure of XFS on > LVM2 on RAID10 on 8x virtual disks, all tasks performing I/O to said XFS > partition hung and I cannot prove or disprove it to be dom0 issue. > > And now the long(er) version: > > On an Amazon EC2 (xen) instance, I had I/O to one of the EBS (Elastic Block > Store virtual disk) devices block with iostat showing one single request > pending. Kernel logs showed hung tasks so after grabbing those I reset the > instance but - while I''m told that Amazon''s logs don''t show any problems > with the EBS - Amazon want the opportunity to exclude an EBS problem by > examining things from the dom0 side while the problem is occurring before > delving into the kernel.Yup, everything is hung waiting for that one IO to complete. Nothing wrong with MD, LVM, or XFS. The problem is either that EBS never completed the IO, or Xen swallowed it and it never made to it to the guest OS. Either way, it does not appear to be a problem in the higher levels of the linux storage stack. Cheers, Dave. -- Dave Chinner david@fromorbit.com
Jason Stubbs
2012-Jun-12 12:11 UTC
Re: PROBLEM: Possible race between xen, md, dm and/or xfs
On 2012-6-12 13:57 , Dave Chinner wrote:> Nothing > wrong with MD, LVM, or XFS. The problem is either that EBS never > completed the IO, or Xen swallowed it and it never made to it to the > guest OS. Either way, it does not appear to be a problem in the > higher levels of the linux storage stack.Thanks Dave for looking into this. I''ll be sure to give Amazon ample opportunity to diagnose things from there side should the issue occur again and hopefully there won''t be any more people reporting extraneous issues. -- Regards, Jason Stubbs
Matt Wilson
2012-Jun-14 00:18 UTC
Re: PROBLEM: Possible race between xen, md, dm and/or xfs
On Tue, Jun 12, 2012 at 05:11:37AM -0700, Jason Stubbs wrote:> On 2012-6-12 13:57 , Dave Chinner wrote: > > Nothing > > wrong with MD, LVM, or XFS. The problem is either that EBS never > > completed the IO, or Xen swallowed it and it never made to it to the > > guest OS. Either way, it does not appear to be a problem in the > > higher levels of the linux storage stack. > > Thanks Dave for looking into this. > > I''ll be sure to give Amazon ample opportunity to diagnose things from > there side should the issue occur again and hopefully there won''t be > any more people reporting extraneous issues.Hi Jason, If you''re able to reproduce this hang, I''m sure that we can get to the root of the problem quite quickly. Short of that, if you can provide a running instance that is exhibiting the problem we can do some live-system debugging. It is much more difficult to determine root cause and verify fixes without reproduction instructions. Given the kernel version you reported in your traces, I can at least rule out one known bug that caused blkfront to wait forever for an IO to complete: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=dffe2e1 The kernel version you''re using using includes the follow-on change to use fasteoi: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=3588fe2 I''m sorry that I can''t be more of more immediate help. If you encounter the problem again, please contact developer support. Matt
Jason Stubbs
2012-Jun-14 00:57 UTC
Re: PROBLEM: Possible race between xen, md, dm and/or xfs
On 2012-6-14 10:18 , Matt Wilson wrote:> On Tue, Jun 12, 2012 at 05:11:37AM -0700, Jason Stubbs wrote: >> I''ll be sure to give Amazon ample opportunity to diagnose things from >> there side should the issue occur again and hopefully there won''t be >> any more people reporting extraneous issues. > > If you''re able to reproduce this hang, I''m sure that we can get to the > root of the problem quite quickly. Short of that, if you can provide a > running instance that is exhibiting the problem we can do some > live-system debugging. It is much more difficult to determine root > cause and verify fixes without reproduction instructions.We''ve got about 50 instances using the same disk layout, but have only been running these new instances for a couple of months. We''ve been using EC2 and EBS for three years now though, which is why I thought it was likely something to do with the disk layout of the new instances. Thinking that, my first concern was to get the instance working again to keep the service running smoothly. Come to think of it though, I think I might have had this issue once before with EBS. Still, that makes two occurrences in somewhere around 70 years combined uptime, so it was either a one off or a very rare corner case. Either way, I think all that can be done is to wait for it to happen again, at which time I''ll take it out of production, leave it running and set up a new instance for production instead.> Given the kernel version you reported in your traces, I can at least > rule out one known bug that caused blkfront to wait forever for an IO > to complete: > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=dffe2e1 > > The kernel version you''re using using includes the follow-on change to > use fasteoi: > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=3588fe2Yep, this is exactly the sort of corner case I though it might be. I''ve confirmed that this change against the sources for the kernel I''m using, though.> I''m sorry that I can''t be more of more immediate help. If you > encounter the problem again, please contact developer support.No problem. We have a support contract and I did go there first, but the response was basically that nothing can be done without the instance running. I supplied the traces, but it wasn''t clear whether they''d actually been investigated or not, hence I chose to report here. In hindsight, I realize I should have kept the instance running, but I don''t tend to think so clearly when it''s the middle of the night. ;) As for not being able to solve the problem, I don''t mind at all. I just wanted to make sure that an adequate attempt had been made to solve the problem. We "architect for failure" as much as possible, so the problem in itself is not such a big deal. Thanks for looking into it! -- Regards, Jason Stubbs