Date:   Fri, 13 Jan 2017 16:33:32 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     osandov@...ndov.com, bart.vanassche@...disk.com
Subject: Re: [PATCHSET v6] blk-mq scheduling framework

On 01/13/2017 04:23 PM, Jens Axboe wrote:
> On 01/13/2017 04:04 AM, Hannes Reinecke wrote:
>> On 01/13/2017 09:15 AM, Hannes Reinecke wrote:
>>> On 01/11/2017 10:39 PM, Jens Axboe wrote:
>>>> Another year, another posting of this patchset. The previous posting
>>>> was here:
>>>>
>>>> https://www.spinics.net/lists/kernel/msg2406106.html
>>>>
>>>> (yes, I've skipped v5, it was fixes on top of v4, not the rework).
>>>>
>>>> I've reworked bits of this to get rid of the shadow requests, thanks
>>>> to Bart for the inspiration. The missing piece, for me, was the fact
>>>> that we have the tags->rqs[] indirection array already. I've done this
>>>> somewhat differently, though, by having the internal scheduler tag
>>>> map be allocated/torn down when an IO scheduler is attached or
>>>> detached. This also means that when we run without a scheduler, we
>>>> don't have to do double tag allocations, it'll work like before.
>>>>
>>>> The patchset applies on top of 4.10-rc3, or can be pulled here:
>>>>
>>>> git://git.kernel.dk/linux-block blk-mq-sched.6
>>>>
>>> Well ... something's wrong here on my machine:
>>>
>>> [   39.886886] ------------[ cut here ]------------
>>> [   39.886895] WARNING: CPU: 9 PID: 62 at block/blk-mq.c:342
>>> __blk_mq_finish_request+0x124/0x140
>>> [   39.886895] Modules linked in: sd_mod ahci uhci_hcd ehci_pci
>>> mpt3sas(+) libahci ehci_hcd serio_raw crc32c_intel raid_class drm libata
>>> usbcore hpsa usb_common scsi_transport_sas sg dm_multipath dm_mod
>>> scsi_dh_rdac scsi_dh_emc scsi_dh_alua autofs4
>>> [   39.886910] CPU: 9 PID: 62 Comm: kworker/u130:0 Not tainted
>>> 4.10.0-rc3+ #528
>>> [   39.886911] Hardware name: HP ProLiant ML350p Gen8, BIOS P72 09/08/2013
>>> [   39.886917] Workqueue: events_unbound async_run_entry_fn
>>> [   39.886918] Call Trace:
>>> [   39.886923]  dump_stack+0x85/0xc9
>>> [   39.886927]  __warn+0xd1/0xf0
>>> [   39.886928]  warn_slowpath_null+0x1d/0x20
>>> [   39.886930]  __blk_mq_finish_request+0x124/0x140
>>> [   39.886932]  blk_mq_finish_request+0x55/0x60
>>> [   39.886934]  blk_mq_sched_put_request+0x78/0x80
>>> [   39.886936]  blk_mq_free_request+0xe/0x10
>>> [   39.886938]  blk_put_request+0x25/0x60
>>> [   39.886944]  __scsi_execute.isra.24+0x104/0x160
>>> [   39.886946]  scsi_execute_req_flags+0x94/0x100
>>> [   39.886948]  scsi_report_opcode+0xab/0x100
>>>
>>> checking ...
>>>
>> Ah.
>> Seems like the elevator switch races with device setup:
>>
>>  1188.490326] ------------[ cut here ]------------
>> [ 1188.490334] WARNING: CPU: 9 PID: 30155 at block/blk-mq.c:342
>> __blk_mq_finish_request+0x172/0x180
>> [ 1188.490335] Modules linked in: mpt3sas(+) raid_class rpcsec_gss_krb5
>> auth_rpcgss nfsv4 nfs lockd grace fscache ebtable_filt
>> er ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables
>> af_packet br_netfilter bridge stp llc iscsi_ibft iscs
>> i_boot_sysfs sb_edac edac_core x86_pkg_temp_thermal intel_powerclamp
>> coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_p
>> clmul tg3 ixgbe ghash_clmulni_intel pcbc ptp aesni_intel pps_core
>> aes_x86_64 ipmi_ssif hpilo hpwdt mdio libphy pcc_cpufreq cry
>> pto_simd glue_helper iTCO_wdt iTCO_vendor_support acpi_cpufreq tpm_tis
>> ipmi_si ipmi_devintf cryptd lpc_ich pcspkr ioatdma tpm_
>> tis_core thermal wmi shpchp dca ipmi_msghandler tpm fjes button sunrpc
>> btrfs xor sr_mod raid6_pq cdrom ehci_pci mgag200 i2c_al
>> go_bit drm_kms_helper syscopyarea sysfillrect uhci_hcd
>> [ 1188.490399]  sysimgblt fb_sys_fops sd_mod ahci ehci_hcd ttm libahci
>> crc32c_intel serio_raw drm libata usbcore usb_common hp
>> sa scsi_transport_sas sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc
>> scsi_dh_alua autofs4
>> [ 1188.490411] CPU: 9 PID: 30155 Comm: kworker/u130:6 Not tainted
>> 4.10.0-rc3+ #535
>> [ 1188.490411] Hardware name: HP ProLiant ML350p Gen8, BIOS P72 09/08/2013
>> [ 1188.490425] Workqueue: events_unbound async_run_entry_fn
>> [ 1188.490427] Call Trace:
>> [ 1188.490433]  dump_stack+0x85/0xc9
>> [ 1188.490436]  __warn+0xd1/0xf0
>> [ 1188.490438]  warn_slowpath_null+0x1d/0x20
>> [ 1188.490440]  __blk_mq_finish_request+0x172/0x180
>> [ 1188.490442]  blk_mq_finish_request+0x55/0x60
>> [ 1188.490443]  blk_mq_sched_put_request+0x78/0x80
>> [ 1188.490445]  blk_mq_free_request+0xe/0x10
>> [ 1188.490448]  blk_put_request+0x25/0x60
>> [ 1188.490453]  __scsi_execute.isra.24+0x104/0x160
>> [ 1188.490455]  scsi_execute_req_flags+0x94/0x100
>> [ 1188.490457]  scsi_report_opcode+0xab/0x100
>> [ 1188.490461]  sd_revalidate_disk+0xaef/0x1450 [sd_mod]
>> [ 1188.490464]  sd_probe_async+0xd1/0x1d0 [sd_mod]
>> [ 1188.490466]  async_run_entry_fn+0x37/0x150
>> [ 1188.490470]  process_one_work+0x1d0/0x660
>> [ 1188.490472]  ? process_one_work+0x151/0x660
>> [ 1188.490474]  worker_thread+0x12b/0x4a0
>> [ 1188.490475]  kthread+0x10c/0x140
>> [ 1188.490477]  ? process_one_work+0x660/0x660
>> [ 1188.490478]  ? kthread_create_on_node+0x40/0x40
>> [ 1188.490483]  ret_from_fork+0x2a/0x40
>> [ 1188.490484] ---[ end trace d5e3a32ac269fc2a ]---
>> [ 1188.490485] rq (487/52) rqs (-1/-1)
>> [ 1188.523518] sd 7:0:0:0: [sdb] Attached SCSI disk
>> [ 1188.540954] elevator: switch to deadline failed
> 
> Where did this last line come from? Do you have a udev rule or something
> that attempts to switch to deadline, which will fail with scsi-mq?
> 
> Trying to get closer to reproducing this, no luck just setting the async
> scan option, mine still boots fine.
> 
Ah, indeed.
There is an ominous udev rule here, trying to switch to 'deadline'.

# cat 60-ssd-scheduler.rules
# do not edit this file, it will be overwritten on update

ACTION!="add", GOTO="ssd_scheduler_end"
SUBSYSTEM!="block", GOTO="ssd_scheduler_end"

IMPORT{cmdline}="elevator"
ENV{elevator}=="*?", GOTO="ssd_scheduler_end"

KERNEL=="sd*[!0-9]", ATTR{queue/rotational}=="0",
ATTR{queue/scheduler}="deadline"

LABEL="ssd_scheduler_end"

Still shouldn't crash the kernel, though ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

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