Re: system hung up when offlining CPUs

From: Hannes Reinecke
Date: Wed Sep 13 2017 - 07:14:20 EST

On 09/12/2017 08:15 PM, YASUAKI ISHIMATSU wrote:
> + linux-scsi and maintainers of megasas
>
> When offlining CPU, I/O stops. Do you have any ideas?
>
> On 09/07/2017 04:23 PM, YASUAKI ISHIMATSU wrote:
>> Hi Mark and Christoph,
>>
>> Sorry for the late reply. I appreciated that you fixed the issue on kvm environment.
>> But the issue still occurs on physical server.
>>
>> Here ares irq information that I summarized megasas irqs from /proc/interrupts
>> and /proc/irq/*/smp_affinity_list on my server:
>>
>> ---
>> IRQ affinity_list IRQ_TYPE
>> 42 0-5 IR-PCI-MSI 1048576-edge megasas
>> 43 0-5 IR-PCI-MSI 1048577-edge megasas
>> 44 0-5 IR-PCI-MSI 1048578-edge megasas
>> 45 0-5 IR-PCI-MSI 1048579-edge megasas
>> 46 0-5 IR-PCI-MSI 1048580-edge megasas
>> 47 0-5 IR-PCI-MSI 1048581-edge megasas
>> 48 0-5 IR-PCI-MSI 1048582-edge megasas
>> 49 0-5 IR-PCI-MSI 1048583-edge megasas
>> 50 0-5 IR-PCI-MSI 1048584-edge megasas
>> 51 0-5 IR-PCI-MSI 1048585-edge megasas
>> 52 0-5 IR-PCI-MSI 1048586-edge megasas
>> 53 0-5 IR-PCI-MSI 1048587-edge megasas
>> 54 0-5 IR-PCI-MSI 1048588-edge megasas
>> 55 0-5 IR-PCI-MSI 1048589-edge megasas
>> 56 0-5 IR-PCI-MSI 1048590-edge megasas
>> 57 0-5 IR-PCI-MSI 1048591-edge megasas
>> 58 0-5 IR-PCI-MSI 1048592-edge megasas
>> 59 0-5 IR-PCI-MSI 1048593-edge megasas
>> 60 0-5 IR-PCI-MSI 1048594-edge megasas
>> 61 0-5 IR-PCI-MSI 1048595-edge megasas
>> 62 0-5 IR-PCI-MSI 1048596-edge megasas
>> 63 0-5 IR-PCI-MSI 1048597-edge megasas
>> 64 0-5 IR-PCI-MSI 1048598-edge megasas
>> 65 0-5 IR-PCI-MSI 1048599-edge megasas
>> 66 24-29 IR-PCI-MSI 1048600-edge megasas
>> 67 24-29 IR-PCI-MSI 1048601-edge megasas
>> 68 24-29 IR-PCI-MSI 1048602-edge megasas
>> 69 24-29 IR-PCI-MSI 1048603-edge megasas
>> 70 24-29 IR-PCI-MSI 1048604-edge megasas
>> 71 24-29 IR-PCI-MSI 1048605-edge megasas
>> 72 24-29 IR-PCI-MSI 1048606-edge megasas
>> 73 24-29 IR-PCI-MSI 1048607-edge megasas
>> 74 24-29 IR-PCI-MSI 1048608-edge megasas
>> 75 24-29 IR-PCI-MSI 1048609-edge megasas
>> 76 24-29 IR-PCI-MSI 1048610-edge megasas
>> 77 24-29 IR-PCI-MSI 1048611-edge megasas
>> 78 24-29 IR-PCI-MSI 1048612-edge megasas
>> 79 24-29 IR-PCI-MSI 1048613-edge megasas
>> 80 24-29 IR-PCI-MSI 1048614-edge megasas
>> 81 24-29 IR-PCI-MSI 1048615-edge megasas
>> 82 24-29 IR-PCI-MSI 1048616-edge megasas
>> 83 24-29 IR-PCI-MSI 1048617-edge megasas
>> 84 24-29 IR-PCI-MSI 1048618-edge megasas
>> 85 24-29 IR-PCI-MSI 1048619-edge megasas
>> 86 24-29 IR-PCI-MSI 1048620-edge megasas
>> 87 24-29 IR-PCI-MSI 1048621-edge megasas
>> 88 24-29 IR-PCI-MSI 1048622-edge megasas
>> 89 24-29 IR-PCI-MSI 1048623-edge megasas
>> ---
>>
>> In my server, IRQ#66-89 are sent to CPU#24-29. And if I offline CPU#24-29,
>> I/O does not work, showing the following messages.
>>
>> ---
>> [...] sd 0:2:0:0: [sda] tag#1 task abort called for scmd(ffff8820574d7560)
>> [...] sd 0:2:0:0: [sda] tag#1 CDB: Read(10) 28 00 0d e8 cf 78 00 00 08 00
>> [...] sd 0:2:0:0: task abort: FAILED scmd(ffff8820574d7560)
>> [...] sd 0:2:0:0: [sda] tag#0 task abort called for scmd(ffff882057426560)
>> [...] sd 0:2:0:0: [sda] tag#0 CDB: Write(10) 2a 00 0d 58 37 00 00 00 08 00
>> [...] sd 0:2:0:0: task abort: FAILED scmd(ffff882057426560)
>> [...] sd 0:2:0:0: target reset called for scmd(ffff8820574d7560)
>> [...] sd 0:2:0:0: [sda] tag#1 megasas: target reset FAILED!!
>> [...] sd 0:2:0:0: [sda] tag#0 Controller reset is requested due to IO timeout
>> [...] SCSI command pointer: (ffff882057426560) SCSI host state: 5 SCSI
>> [...] IO request frame:
>> [...]
>> <snip>
>> [...]
>> [...] megaraid_sas 0000:02:00.0: [ 0]waiting for 2 commands to complete for scsi0
>> [...] INFO: task auditd:1200 blocked for more than 120 seconds.
>> [...] Not tainted 4.13.0+ #15
>> [...] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [...] auditd D 0 1200 1 0x00000000
>> [...] Call Trace:
>> [...] __schedule+0x28d/0x890
>> [...] schedule+0x36/0x80
>> [...] io_schedule+0x16/0x40
>> [...] wait_on_page_bit_common+0x109/0x1c0
>> [...] ? page_cache_tree_insert+0xf0/0xf0
>> [...] __filemap_fdatawait_range+0x127/0x190
>> [...] ? __filemap_fdatawrite_range+0xd1/0x100
>> [...] file_write_and_wait_range+0x60/0xb0
>> [...] xfs_file_fsync+0x67/0x1d0 [xfs]
>> [...] vfs_fsync_range+0x3d/0xb0
>> [...] do_fsync+0x3d/0x70
>> [...] SyS_fsync+0x10/0x20
>> [...] entry_SYSCALL_64_fastpath+0x1a/0xa5
>> [...] RIP: 0033:0x7f0bd9633d2d
>> [...] RSP: 002b:00007f0bd751ed30 EFLAGS: 00000293 ORIG_RAX: 000000000000004a
>> [...] RAX: ffffffffffffffda RBX: 00005590566d0080 RCX: 00007f0bd9633d2d
>> [...] RDX: 00005590566d1260 RSI: 0000000000000000 RDI: 0000000000000005
>> [...] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000017
>> [...] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
>> [...] R13: 00007f0bd751f9c0 R14: 00007f0bd751f700 R15: 0000000000000000
>> ---
>>
>> Thanks,
>> Yasuaki Ishimatsu
>>

This indeed looks like a problem.
We're going to great lengths to submit and complete I/O on the same CPU,
so if the CPU is offlined while I/O is in flight we won't be getting a
completion for this particular I/O.
However, the megasas driver should be able to cope with this situation;
after all, the firmware maintains completions queues, so it would be
dead easy to look at _other_ completions queues, too, if a timeout occurs.
Also the IRQ affinity looks bogus (we should spread IRQs to _all_ CPUs,
not just a subset), and the driver should make sure to receive
completions even if the respective CPUs are offlined.
Alternatively it should not try to submit a command abort via an
offlined CPUs; that's guaranteed to run into the same problems.

So it looks more like a driver issue to me...

Cheers,

Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
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