Date:   Sat, 03 Jul 2021 00:07:53 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Jan Kara <jack@...e.cz>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Luca Mariotti <mariottiluca1@...mail.it>,
        Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Pietro Pedroni <pedroni.pietro.96@...il.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Khazhy Kumykov <khazhy@...gle.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH FIXES/IMPROVEMENTS 0/7] block, bfq: preserve control, boost throughput, fix bugs

Hello.

On úterý 22. června 2021 18:29:48 CEST Jan Kara wrote:
> On Tue 22-06-21 09:35:05, Oleksandr Natalenko wrote:
> > On úterý 22. června 2021 9:08:43 CEST Paolo Valente wrote:
> > > CCing also Jan and Khazhy, because in your commit log I see also the
> > > commit on bfq_requests_merged().
> > > 
> > > Is this OOPS reproducible for you?
> > 
> > No, I haven't found a reproducer, at least yet. It took half a day of
> > uptime to hit this, so might not be that easy.
> 
> Hum, if you can acquire a crash dump it would be the easiest I guess. We'd
> need to find out more about the request we crash on - whether it's
> otherwise valid, in what state it is etc...

Still have no reliable reproducer and no vmcore, however I'm running v5.13 
with the following patches applied on top of it:

```
blk: Fix lock inversion between ioc lock and bfqd lock
bfq: Remove merged request already in bfq_requests_merged()
block: Remove unnecessary elevator operation checks
block: Do not pull requests from the scheduler when we cannot dispatch them
block, bfq: reset waker pointer with shared queues
block, bfq: check waker only for queues with no in-flight I/O
block, bfq: avoid delayed merge of async queues
block, bfq: boost throughput by extending queue-merging times
block, bfq: consider also creation time in delayed stable merge
block, bfq: fix delayed stable merge check
block, bfq: let also stably merged queues enjoy weight raising
```

and just got the following crash:

```
[60313.522570] ------------[ cut here ]------------
[60313.522579] WARNING: CPU: 20 PID: 388 at arch/x86/include/asm/kfence.h:44 
kfence_protect_page+0x39/0xc0
[60313.522586] Modules linked in: sctp ip6_udp_tunnel udp_tunnel uinput 
netconsole blocklayoutdriver rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver 
nfs lockd grace sunrpc fscache netfs rfcomm nft_ct nf_conntrack nf_defrag_ipv6 
nf_defrag_ipv4 cmac algif_hash algif_skcipher nf_tables af_alg bnep tun 
nfnetlink nls_iso8859_1 intel_rapl_msr vfat intel_rapl_common iwlmvm fat 
mac80211 edac_mce_amd libarc4 btusb eeepc_wmi btrtl asus_wmi iwlwifi btbcm 
snd_usb_audio sparse_keymap kvm_amd video wmi_bmof mxm_wmi btintel uvcvideo 
snd_hda_codec_realtek videobuf2_vmalloc videobuf2_memops snd_usbmidi_lib kvm 
snd_hda_codec_generic bluetooth videobuf2_v4l2 ledtrig_audio 
snd_hda_codec_hdmi joydev snd_rawmidi ecdh_generic irqbypass ecc snd_hda_intel 
mousedev pl2303 cfg80211 snd_seq_device videobuf2_common crc16 rapl k10temp 
snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec igb r8169 sp5100_tco 
snd_hda_core realtek i2c_piix4 ipmi_devintf dca snd_hwdep mdio_devres rfkill 
snd_pcm libphy ipmi_msghandler wmi
[60313.522630]  pinctrl_amd mac_hid acpi_cpufreq tcp_bbr2 vhost_vsock 
vmw_vsock_virtio_transport_common vhost vhost_iotlb vsock v4l2loopback 
videodev mc snd_hrtimer snd_timer snd soundcore nct6775 hwmon_vid crypto_user 
fuse ip_tables x_tables xfs dm_thin_pool dm_persistent_data dm_bio_prison 
dm_bufio libcrc32c crc32c_generic dm_crypt cbc encrypted_keys trusted 
asn1_encoder tee hid_logitech_hidpp hid_logitech_dj usbhid dm_mod 
crct10dif_pclmul crc32_pclmul crc32c_intel raid10 ghash_clmulni_intel 
aesni_intel md_mod crypto_simd cryptd amdgpu ccp xhci_pci xhci_pci_renesas 
tpm_crb tpm_tis tpm_tis_core tpm rng_core drm_ttm_helper ttm gpu_sched 
i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec 
drm agpgart
[60313.522665] CPU: 20 PID: 388 Comm: kworker/20:1H Tainted: G        W         
5.13.0-pf2 #1
[60313.522668] Hardware name: ASUS System Product Name/Pro WS X570-ACE, BIOS 
3601 05/26/2021
[60313.522671] Workqueue: kblockd blk_mq_run_work_fn
[60313.522675] RIP: 0010:kfence_protect_page+0x39/0xc0
[60313.522679] Code: 04 65 48 8b 04 25 28 00 00 00 48 89 44 24 08 31 c0 c7 44 
24 04 00 00 00 00 e8 83 20 d5 ff 48 85 c0 74 07 83 7c 24 04 01 74 06 <0f> 0b 31 
c0 eb 4c 48 8b 38 48 89 c2 84 db 75 59 48 89 f8 0f 1f 40
[60313.522682] RSP: 0018:ffffb559c0affb28 EFLAGS: 00010046
[60313.522684] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffb559c0affb2c
[60313.522687] RDX: ffffb559c0affb2c RSI: 0000000000000000 RDI: 0000000000000000
[60313.522690] RBP: 0000000000000000 R08: 0000000000000000 R09: 
0000000000000000
[60313.522692] R10: 0000000000000000 R11: 0000000000000000 R12: 
0000000000000002
[60313.522694] R13: ffffb559c0affc28 R14: 00000000c0affc01 R15: 0000000000000000
[60313.522696] FS:  0000000000000000(0000) GS:ffff8cf44ef00000(0000) knlGS:
0000000000000000
[60313.522698] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60313.522700] CR2: 0000000000000120 CR3: 000000013ebce000 CR4: 
0000000000350ee0
[60313.522702] Call Trace:
[60313.522707]  kfence_handle_page_fault+0xa6/0x280
[60313.522710]  page_fault_oops+0x9d/0x2d0
[60313.522714]  exc_page_fault+0x78/0x180
[60313.522718]  asm_exc_page_fault+0x1e/0x30
[60313.522721] RIP: 0010:bfq_dispatch_request+0x4c3/0x1280
[60313.522725] Code: 4c 89 e7 e8 ef da ff ff 4c 89 ff 89 c6 e8 75 64 00 00 4c 39 
bb a0 00 00 00 0f 84 86 04 00 00 49 8b 84 24 90 00 00 00 48 8b 33 <ff> 80 20 01 
00 00 48 89 34 24 48 8b 46 08 4c 8b 58 08 4c 89 5c 24
[60313.522727] RSP: 0018:ffffb559c0affcd0 EFLAGS: 00010046
[60313.522729] RAX: 0000000000000000 RBX: ffff8ced4d6a1000 RCX: 0000000000000000
[60313.522731] RDX: 0000000000000000 RSI: ffff8ced4ad90000 RDI: ffff8ced52fc9f40
[60313.522733] RBP: 0000000000000000 R08: 0000000000000001 R09: 
0000000000000000
[60313.522735] R10: 000000000000003f R11: 0000000000000000 R12: ffff8cf20e5a5400
[60313.522737] R13: ffff8cf0e7e91c70 R14: ffff8ced4d6a1420 R15: ffff8cf0e7e91c70
[60313.522741]  ? mod_delayed_work_on+0x71/0xe0
[60313.522745]  ? __sbitmap_get_word+0x30/0x80
[60313.522748]  __blk_mq_do_dispatch_sched+0x218/0x320
[60313.522752]  __blk_mq_sched_dispatch_requests+0x107/0x150
[60313.522755]  blk_mq_sched_dispatch_requests+0x2f/0x60
[60313.522758]  blk_mq_run_work_fn+0x43/0xc0
[60313.522761]  process_one_work+0x24e/0x430
[60313.522765]  worker_thread+0x54/0x4d0
[60313.522767]  ? process_one_work+0x430/0x430
[60313.522770]  kthread+0x182/0x1b0
[60313.522773]  ? __kthread_init_worker+0x50/0x50
[60313.522776]  ret_from_fork+0x22/0x30
[60313.522781] ---[ end trace 55ef262e614b59af ]---
[60313.522786] ------------[ cut here ]------------
[60313.522787] WARNING: CPU: 20 PID: 388 at mm/kfence/core.c:135 
kfence_handle_page_fault+0xaa/0x280
[60313.522791] Modules linked in: sctp ip6_udp_tunnel udp_tunnel uinput 
netconsole blocklayoutdriver rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver 
nfs lockd grace sunrpc fscache netfs rfcomm nft_ct nf_conntrack nf_defrag_ipv6 
nf_defrag_ipv4 cmac algif_hash algif_skcipher nf_tables af_alg bnep tun 
nfnetlink nls_iso8859_1 intel_rapl_msr vfat intel_rapl_common iwlmvm fat 
mac80211 edac_mce_amd libarc4 btusb eeepc_wmi btrtl asus_wmi iwlwifi btbcm 
snd_usb_audio sparse_keymap kvm_amd video wmi_bmof mxm_wmi btintel uvcvideo 
snd_hda_codec_realtek videobuf2_vmalloc videobuf2_memops snd_usbmidi_lib kvm 
snd_hda_codec_generic bluetooth videobuf2_v4l2 ledtrig_audio 
snd_hda_codec_hdmi joydev snd_rawmidi ecdh_generic irqbypass ecc snd_hda_intel 
mousedev pl2303 cfg80211 snd_seq_device videobuf2_common crc16 rapl k10temp 
snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec igb r8169 sp5100_tco 
snd_hda_core realtek i2c_piix4 ipmi_devintf dca snd_hwdep mdio_devres rfkill 
snd_pcm libphy ipmi_msghandler wmi
[60313.522817]  pinctrl_amd mac_hid acpi_cpufreq tcp_bbr2 vhost_vsock 
vmw_vsock_virtio_transport_common vhost vhost_iotlb vsock v4l2loopback 
videodev mc snd_hrtimer snd_timer snd soundcore nct6775 hwmon_vid crypto_user 
fuse ip_tables x_tables xfs dm_thin_pool dm_persistent_data dm_bio_prison 
dm_bufio libcrc32c crc32c_generic dm_crypt cbc encrypted_keys trusted 
asn1_encoder tee hid_logitech_hidpp hid_logitech_dj usbhid dm_mod 
crct10dif_pclmul crc32_pclmul crc32c_intel raid10 ghash_clmulni_intel 
aesni_intel md_mod crypto_simd cryptd amdgpu ccp xhci_pci xhci_pci_renesas 
tpm_crb tpm_tis tpm_tis_core tpm rng_core drm_ttm_helper ttm gpu_sched 
i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec 
drm agpgart
[60313.522840] CPU: 20 PID: 388 Comm: kworker/20:1H Tainted: G        W         
5.13.0-pf2 #1
[60313.522843] Hardware name: ASUS System Product Name/Pro WS X570-ACE, BIOS 
3601 05/26/2021
[60313.522845] Workqueue: kblockd blk_mq_run_work_fn
[60313.522848] RIP: 0010:kfence_handle_page_fault+0xaa/0x280
[60313.522851] Code: 0f 86 d4 00 00 00 0f b6 f3 41 b8 03 00 00 00 31 c9 4c 89 
ea 48 89 ef e8 e4 05 00 00 31 f6 4c 89 ff e8 6a f5 ff ff 84 c0 75 8d <0f> 0b c6 
05 7d fd 6b 01 00 45 31 f6 e9 7c ff ff ff 48 8b 0d 36 a0
[60313.522853] RSP: 0018:ffffb559c0affb50 EFLAGS: 00010046
[60313.522855] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffb559c0affb2c
[60313.522857] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 
0000000000000000
[60313.522859] RBP: 0000000000000120 R08: 0000000000000000 R09: 
0000000000000000
[60313.522860] R10: 0000000000000000 R11: 0000000000000000 R12: 
0000000000000002
[60313.522862] R13: ffffb559c0affc28 R14: 00000000c0affc01 R15: 0000000000000000
[60313.522864] FS:  0000000000000000(0000) GS:ffff8cf44ef00000(0000) knlGS:
0000000000000000
[60313.522866] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60313.522868] CR2: 0000000000000120 CR3: 000000013ebce000 CR4: 
0000000000350ee0
[60313.522870] Call Trace:
[60313.522872]  page_fault_oops+0x9d/0x2d0
[60313.522875]  exc_page_fault+0x78/0x180
[60313.522878]  asm_exc_page_fault+0x1e/0x30
[60313.522880] RIP: 0010:bfq_dispatch_request+0x4c3/0x1280
[60313.522883] Code: 4c 89 e7 e8 ef da ff ff 4c 89 ff 89 c6 e8 75 64 00 00 4c 39 
bb a0 00 00 00 0f 84 86 04 00 00 49 8b 84 24 90 00 00 00 48 8b 33 <ff> 80 20 01 
00 00 48 89 34 24 48 8b 46 08 4c 8b 58 08 4c 89 5c 24
[60313.522885] RSP: 0018:ffffb559c0affcd0 EFLAGS: 00010046
[60313.522887] RAX: 0000000000000000 RBX: ffff8ced4d6a1000 RCX: 0000000000000000
[60313.522889] RDX: 0000000000000000 RSI: ffff8ced4ad90000 RDI: ffff8ced52fc9f40
[60313.522890] RBP: 0000000000000000 R08: 0000000000000001 R09: 
0000000000000000
[60313.522892] R10: 000000000000003f R11: 0000000000000000 R12: ffff8cf20e5a5400
[60313.523148] R13: ffff8cf0e7e91c70 R14: ffff8ced4d6a1420 R15: ffff8cf0e7e91c70
[60313.523150]  ? mod_delayed_work_on+0x71/0xe0
[60313.523153]  ? __sbitmap_get_word+0x30/0x80
[60313.523157]  __blk_mq_do_dispatch_sched+0x218/0x320
[60313.523161]  __blk_mq_sched_dispatch_requests+0x107/0x150
[60313.523165]  blk_mq_sched_dispatch_requests+0x2f/0x60
[60313.523167]  blk_mq_run_work_fn+0x43/0xc0
[60313.523170]  process_one_work+0x24e/0x430
[60313.523173]  worker_thread+0x54/0x4d0
[60313.523176]  ? process_one_work+0x430/0x430
[60313.523178]  kthread+0x182/0x1b0
[60313.523181]  ? __kthread_init_worker+0x50/0x50
[60313.523183]  ret_from_fork+0x22/0x30
[60313.523187] ---[ end trace 55ef262e614b59b0 ]---
[60313.523189] BUG: kernel NULL pointer dereference, address: 0000000000000120
[60313.523191] #PF: supervisor write access in kernel mode
[60313.523193] #PF: error_code(0x0002) - not-present page
[60313.523195] PGD 0 P4D 0 
[60313.523197] Oops: 0002 [#1] PREEMPT SMP NOPTI
[60313.523200] CPU: 20 PID: 388 Comm: kworker/20:1H Tainted: G        W         
5.13.0-pf2 #1
[60313.523202] Hardware name: ASUS System Product Name/Pro WS X570-ACE, BIOS 
3601 05/26/2021
[60313.523204] Workqueue: kblockd blk_mq_run_work_fn
[60313.523207] RIP: 0010:bfq_dispatch_request+0x4c3/0x1280
[60313.523210] Code: 4c 89 e7 e8 ef da ff ff 4c 89 ff 89 c6 e8 75 64 00 00 4c 39 
bb a0 00 00 00 0f 84 86 04 00 00 49 8b 84 24 90 00 00 00 48 8b 33 <ff> 80 20 01 
00 00 48 89 34 24 48 8b 46 08 4c 8b 58 08 4c 89 5c 24
[60313.523213] RSP: 0018:ffffb559c0affcd0 EFLAGS: 00010046
[60313.523215] RAX: 0000000000000000 RBX: ffff8ced4d6a1000 RCX: 0000000000000000
[60313.523216] RDX: 0000000000000000 RSI: ffff8ced4ad90000 RDI: ffff8ced52fc9f40
[60313.523218] RBP: 0000000000000000 R08: 0000000000000001 R09: 
0000000000000000
[60313.523220] R10: 000000000000003f R11: 0000000000000000 R12: ffff8cf20e5a5400
[60313.523221] R13: ffff8cf0e7e91c70 R14: ffff8ced4d6a1420 R15: ffff8cf0e7e91c70
[60313.523223] FS:  0000000000000000(0000) GS:ffff8cf44ef00000(0000) knlGS:
0000000000000000
[60313.523225] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60313.523227] CR2: 0000000000000120 CR3: 000000013ebce000 CR4: 
0000000000350ee0
[60313.523229] Call Trace:
[60313.523231]  ? mod_delayed_work_on+0x71/0xe0
[60313.523233]  ? __sbitmap_get_word+0x30/0x80
[60313.523237]  __blk_mq_do_dispatch_sched+0x218/0x320
[60313.523240]  __blk_mq_sched_dispatch_requests+0x107/0x150
[60313.523243]  blk_mq_sched_dispatch_requests+0x2f/0x60
[60313.523246]  blk_mq_run_work_fn+0x43/0xc0
[60313.523249]  process_one_work+0x24e/0x430
[60313.523251]  worker_thread+0x54/0x4d0
[60313.523254]  ? process_one_work+0x430/0x430
[60313.523257]  kthread+0x182/0x1b0
[60313.523259]  ? __kthread_init_worker+0x50/0x50
[60313.523261]  ret_from_fork+0x22/0x30
[60313.523265] Modules linked in: sctp ip6_udp_tunnel udp_tunnel uinput 
netconsole blocklayoutdriver rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver 
nfs lockd grace sunrpc fscache netfs rfcomm nft_ct nf_conntrack nf_defrag_ipv6 
nf_defrag_ipv4 cmac algif_hash algif_skcipher nf_tables af_alg bnep tun 
nfnetlink nls_iso8859_1 intel_rapl_msr vfat intel_rapl_common iwlmvm fat 
mac80211 edac_mce_amd libarc4 btusb eeepc_wmi btrtl asus_wmi iwlwifi btbcm 
snd_usb_audio sparse_keymap kvm_amd video wmi_bmof mxm_wmi btintel uvcvideo 
snd_hda_codec_realtek videobuf2_vmalloc videobuf2_memops snd_usbmidi_lib kvm 
snd_hda_codec_generic bluetooth videobuf2_v4l2 ledtrig_audio 
snd_hda_codec_hdmi joydev snd_rawmidi ecdh_generic irqbypass ecc snd_hda_intel 
mousedev pl2303 cfg80211 snd_seq_device videobuf2_common crc16 rapl k10temp 
snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec igb r8169 sp5100_tco 
snd_hda_core realtek i2c_piix4 ipmi_devintf dca snd_hwdep mdio_devres rfkill 
snd_pcm libphy ipmi_msghandler wmi
[60313.523290]  pinctrl_amd mac_hid acpi_cpufreq tcp_bbr2 vhost_vsock 
vmw_vsock_virtio_transport_common vhost vhost_iotlb vsock v4l2loopback 
videodev mc snd_hrtimer snd_timer snd soundcore nct6775 hwmon_vid crypto_user 
fuse ip_tables x_tables xfs dm_thin_pool dm_persistent_data dm_bio_prison 
dm_bufio libcrc32c crc32c_generic dm_crypt cbc encrypted_keys trusted 
asn1_encoder tee hid_logitech_hidpp hid_logitech_dj usbhid dm_mod 
crct10dif_pclmul crc32_pclmul crc32c_intel raid10 ghash_clmulni_intel 
aesni_intel md_mod crypto_simd cryptd amdgpu ccp xhci_pci xhci_pci_renesas 
tpm_crb tpm_tis tpm_tis_core tpm rng_core drm_ttm_helper ttm gpu_sched 
i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec 
drm agpgart
[60313.523314] CR2: 0000000000000120
[60313.523316] ---[ end trace 55ef262e614b59b1 ]---
[60313.523318] RIP: 0010:bfq_dispatch_request+0x4c3/0x1280
[60313.523321] Code: 4c 89 e7 e8 ef da ff ff 4c 89 ff 89 c6 e8 75 64 00 00 4c 39 
bb a0 00 00 00 0f 84 86 04 00 00 49 8b 84 24 90 00 00 00 48 8b 33 <ff> 80 20 01 
00 00 48 89 34 24 48 8b 46 08 4c 8b 58 08 4c 89 5c 24
[60313.523323] RSP: 0018:ffffb559c0affcd0 EFLAGS: 00010046
[60313.523325] RAX: 0000000000000000 RBX: ffff8ced4d6a1000 RCX: 0000000000000000
[60313.523326] RDX: 0000000000000000 RSI: ffff8ced4ad90000 RDI: ffff8ced52fc9f40
[60313.523328] RBP: 0000000000000000 R08: 0000000000000001 R09: 
0000000000000000
[60313.523330] R10: 000000000000003f R11: 0000000000000000 R12: ffff8cf20e5a5400
[60313.523332] R13: ffff8cf0e7e91c70 R14: ffff8ced4d6a1420 R15: ffff8cf0e7e91c70
[60313.523334] FS:  0000000000000000(0000) GS:ffff8cf44ef00000(0000) knlGS:
0000000000000000
[60313.523336] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60313.523338] CR2: 0000000000000120 CR3: 000000013ebce000 CR4: 
0000000000350ee0
[60313.523339] note: kworker/20:1H[388] exited with preempt_count 1
```

-- 
Oleksandr Natalenko (post-factum)

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