Re: [PATCHSET v6] blk-mq scheduling framework

[Hannes Reinecke <hare@suse.de>]

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

(The 'rqs' line is a debug output from me:

			struct request *rqs_rq =
				hctx->tags->rqs[rq->tag];

			printk(KERN_WARNING "rq (%d/%d) rqs (%d/%d)\n",
			       rq->tag, sched_tag,
			       rqs_rq ? rqs_rq->tag : -1,
			       rqs_rq ? rqs_rq->internal_tag : -1);

telling us that request with 'tag' 487 is _not_ at position
487 in the rqs array; rather that position is empty.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
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