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Message-ID: <71576a9ff7398bfa4b8c0a1a1a2523383b056168.camel@gekmihesg.de>
Subject: Re: bcache: kernel NULL pointer dereference since 6.1.39
From:   Markus Weippert <markus@gekmihesg.de>
To:     Thorsten Leemhuis <regressions@leemhuis.info>,
        Zheng Wang <zyytlz.wz@163.com>, Coly Li <colyli@suse.de>
Cc:     linux-kernel@vger.kernel.org,
        Stefan =?ISO-8859-1?Q?F=F6rster?= <cite@incertum.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Linux kernel regressions list <regressions@lists.linux.dev>,
        linux-bcache@vger.kernel.org
Date:   Fri, 24 Nov 2023 14:29:14 +0100
In-Reply-To: <be371028-efeb-44af-90ea-5c307f27d4c6@leemhuis.info>
References: <ZV9ZSyDLNDlzutgQ@pharmakeia.incertum.net>
         <be371028-efeb-44af-90ea-5c307f27d4c6@leemhuis.info>
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> On 23.11.23 14:53, Stefan F=C3=B6rster wrote:
> >=20
> > starting with kernel 6.1.39, we see the following error message
> > with
> > heavy I/O loads. We needed to revert
>=20
> Thx for the report. I assume that problem still occurs with the
> latest
> 6.1.y kernel?
>=20
> > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit=
/?h=3Dv6.1.39&id=3D68118c339c6e1e16ae017bef160dbe28a27ae9c8
>=20
> FWIW, that is mainline commit 028ddcac477b69 ("bcache: Remove
> unnecessary NULL point check in node allocations") [v6.5-rc1].
>=20
> Did a quick check and noticed a fix for that change was recently
> mainlined as f72f4312d43883 ("bcache: replace a mistaken IS_ERR() by
> IS_ERR_OR_NULL() in btree_gc_coalesce()") [v6.7-rc2-post]:
> https://lore.kernel.org/all/20231118163852.9692-1-colyli@suse.de/
>=20
> It is expected to soon be interegrated into a 6.1.y kernel.
>=20
> But maybe it's something else. I CCed the involved people, they might
> know.

We applied f72f4312d43883 to the current Debian kernel (based on
6.1.55) but it didn't help, same stack trace.
Looking at the description, __bch_btree_node_alloc() should never be
able to return NULL anyway after
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=
=3Dv6.1.39&id=3D7ecea5ce3dc17339c280c75b58ac93d8c8620d9f
But I didn't verify all callers, so this might still be correct, if
it's not always initialized with the return value of
__bch_btree_node_alloc().

Anyway, I think we fixed it by applying this:

diff -Naurp a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
--- a/drivers/md/bcache/btree.c	2023-09-23 11:11:13.000000000 +0200
+++ b/drivers/md/bcache/btree.c	2023-11-24 13:13:09.840013759 +0100
@@ -1489,7 +1489,7 @@ out_nocoalesce:
 	bch_keylist_free(&keylist);
=20
 	for (i =3D 0; i < nodes; i++)
-		if (!IS_ERR(new_nodes[i])) {
+		if (!IS_ERR_OR_NULL(new_nodes[i])) {
 			btree_node_free(new_nodes[i]);
 			rw_unlock(true, new_nodes[i]);
 		}

--

That seems to run stable now. I suppose the culprit is here:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drive=
rs/md/bcache/btree.c?h=3Dv6.1.55#n1448

	new_nodes[0] =3D NULL;

	for (i =3D 0; i < nodes; i++) {
		if (__bch_keylist_realloc(&keylist, bkey_u64s(&r[i].b-
>key)))
			goto out_nocoalesce;


So if __bch_keylist_realloc() succeeds, then btree_node_free() will be
called with new_nodes[0] which is NULL.

This is still the same in mainline:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/dri=
vers/md/bcache/btree.c?id=3D31f5b956a197d4ec25c8a07cb3a2ab69d0c0b82f#n1481


>=20
> Ciao, Thorsten
>=20
> > to make sure the systems don't suddenly get stuck.
> >=20
> > 1. Kernel 6.6.2-arch1-1 on Dell Latitude:
> >=20
> > [16816.214942] BUG: kernel NULL pointer dereference, address:
> > 0000000000000080
> > [16816.214948] #PF: supervisor read access in kernel mode
> > [16816.214951] #PF: error_code(0x0000) - not-present page
> > [16816.214953] PGD 0 P4D 0 [16816.214956] Oops: 0000 [#1] PREEMPT
> > SMP NOPTI
> > [16816.214960] CPU: 7 PID: 83416 Comm: bcache_gc Tainted:
> > P=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> > OE=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 6.6.2-arch1-1 #1 11215f9ba7ddfb5164467=
4a5b2ced71612c62fe9
> > [16816.214964] Hardware name: Dell Inc. Latitude 5431/06F77M, BIOS
> > 1.17.0 09/21/2023
> > [16816.214965] RIP: 0010:btree_node_free+0xf/0x160 [bcache]
> > [16816.214999] Code: 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90
> > 90 90
> > 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 55 53 48 89 fb 0f 1f
> > 44 00
> > 00 <48> 8b 83 80 00 00 00 48 8d ab 90 00 00 00 48 39 98 60 c3 00 00
> > 75
> > [16816.215001] RSP: 0018:ffffc90021777af8 EFLAGS: 00010207
> > [16816.215004] RAX: 0000000000000001 RBX: 0000000000000000 RCX:
> > ffff888515ce0670
> > [16816.215006] RDX: 0000000000000000 RSI: ffff888515ce0680 RDI:
> > 0000000000000000
> > [16816.215007] RBP: ffffc90021777bf0 R08: ffff88819476d9e0 R09:
> > 00000000013ffde8
> > [16816.215009] R10: 0000000000000000 R11: ffffc9000061b000 R12:
> > ffffc90021777e40
> > [16816.215010] R13: ffffc90021777bf0 R14: ffffc90021777bd8 R15:
> > ffff88819476c000
> > [16816.215011] FS:=C2=A0 0000000000000000(0000)
> > GS:ffff88886fdc0000(0000)
> > knlGS:0000000000000000
> > [16816.215013] CS:=C2=A0 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [16816.215015] CR2: 0000000000000080 CR3: 0000000294a20000 CR4:
> > 0000000000f50ee0
> > [16816.215017] PKRU: 55555554
> > [16816.215018] Call Trace:
> > [16816.215021]=C2=A0 <TASK>
> > [16816.215024]=C2=A0 ? __die+0x23/0x70
> > [16816.215030]=C2=A0 ? page_fault_oops+0x171/0x4e0
> > [16816.215035]=C2=A0 ? __pfx_bch_ptr_bad+0x10/0x10 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215059]=C2=A0 ? exc_page_fault+0x7f/0x180
> > [16816.215065]=C2=A0 ? asm_exc_page_fault+0x26/0x30
> > [16816.215070]=C2=A0 ? btree_node_free+0xf/0x160 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215095]=C2=A0 ? btree_node_free+0xa3/0x160 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215118]=C2=A0 btree_gc_coalesce+0x2a7/0x890 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215144]=C2=A0 ? bch_extent_bad+0x81/0x190 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215172]=C2=A0 btree_gc_recurse+0x130/0x390 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215197]=C2=A0 ? btree_gc_mark_node+0x72/0x240 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215221]=C2=A0 bch_btree_gc+0x4b6/0x620 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215246]=C2=A0 ? __pfx_autoremove_wake_function+0x10/0x10
> > [16816.215250]=C2=A0 ? __pfx_bch_gc_thread+0x10/0x10 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215272]=C2=A0 bch_gc_thread+0x139/0x190 [bcache
> > 33eebe64448bb81d5f2a10179a48eb0a5bdb25a6]
> > [16816.215295]=C2=A0 ? __pfx_autoremove_wake_function+0x10/0x10
> > [16816.215298]=C2=A0 kthread+0xe5/0x120
> > [16816.215302]=C2=A0 ? __pfx_kthread+0x10/0x10
> > [16816.215306]=C2=A0 ret_from_fork+0x31/0x50
> > [16816.215309]=C2=A0 ? __pfx_kthread+0x10/0x10
> > [16816.215312]=C2=A0 ret_from_fork_asm+0x1b/0x30
> > [16816.215318]=C2=A0 </TASK>
> > [16816.215319] Modules linked in: bcache tun ccm rfcomm
> > snd_seq_dummy
> > snd_hrtimer snd_seq nvidia(POE) typec_displayport cmac algif_hash
> > algif_skcipher af_alg bnep hid_sensor_custom hid_sensor_hub
> > intel_ishtp_hid snd_hda_codec_hdmi snd_sof_pci_intel_tgl
> > snd_sof_intel_hda_common soundwire_intel snd_sof_intel_hda_mlink
> > soundwire_cadence snd_sof_intel_hda snd_sof_pci snd_sof_xtensa_dsp
> > snd_sof snd_sof_utils intel_uncore_frequency
> > intel_uncore_frequency_common snd_ctl_led snd_soc_hdac_hda
> > r8153_ecm
> > snd_hda_ext_core iwlmvm cdc_ether snd_soc_acpi_intel_match usbnet
> > snd_soc_acpi soundwire_generic_allocation soundwire_bus
> > snd_soc_core
> > x86_pkg_temp_thermal snd_compress snd_hda_codec_realtek
> > intel_powerclamp
> > ac97_bus snd_hda_codec_generic dell_rbtn coretemp btusb
> > snd_pcm_dmaengine snd_usb_audio mac80211 btrtl snd_hda_intel
> > kvm_intel
> > btintel snd_intel_dspcfg snd_intel_sdw_acpi snd_usbmidi_lib btbcm
> > dell_laptop snd_ump btmtk libarc4 snd_hda_codec uvcvideo kvm
> > snd_rawmidi
> > bluetooth snd_hda_core videobuf2_vmalloc hid_multitouch iwlwifi
> > [16816.215367]=C2=A0 dell_wmi snd_hwdep iTCO_wdt snd_seq_device uvc
> > nls_iso8859_1 videobuf2_memops dell_smbios intel_pmc_bxt mei_hdcp
> > mei_pxp spi_nor snd_pcm processor_thermal_device_pci r8152
> > videobuf2_v4l2 dell_wmi_sysman irqbypass intel_rapl_msr dcdbas vfat
> > iTCO_vendor_support fat rapl intel_cstate intel_uncore psmouse
> > pcspkr
> > dell_wmi_ddv firmware_attributes_class ledtrig_audio
> > videobuf2_common
> > ucsi_acpi dell_wmi_descriptor processor_thermal_device mousedev
> > ecdh_generic snd_timer mii joydev mtd wmi_bmof e1000e cfg80211
> > processor_thermal_rfim mei_me intel_lpss_pci i2c_i801 snd
> > processor_thermal_mbox typec_ucsi intel_ish_ipc intel_lpss mei
> > soundcore
> > i2c_smbus processor_thermal_rapl rfkill thunderbolt typec idma64
> > intel_ishtp roles intel_rapl_common igen6_edac i2c_hid_acpi
> > int3403_thermal i2c_hid int340x_thermal_zone intel_hid
> > int3400_thermal
> > acpi_thermal_rel sparse_keymap acpi_tad acpi_pad mac_hid
> > vboxnetflt(OE)
> > vboxnetadp(OE) vboxdrv(OE) v4l2loopback(OE) videodev mc i2c_dev
> > crypto_user fuse loop ip_tables x_tables ext4
> > [16816.215420]=C2=A0 crc32c_generic crc16 mbcache jbd2 dm_crypt cbc
> > encrypted_keys trusted asn1_encoder tee usbhid i915 dm_mod
> > crct10dif_pclmul crc32_pclmul crc32c_intel polyval_clmulni
> > i2c_algo_bit
> > polyval_generic serio_raw rtsx_pci_sdmmc drm_buddy gf128mul atkbd
> > ghash_clmulni_intel ttm mmc_core sha512_ssse3 libps2 vivaldi_fmap
> > intel_gtt aesni_intel nvme crypto_simd drm_display_helper video
> > nvme_core cryptd spi_intel_pci rtsx_pci spi_intel i8042 xhci_pci
> > cec
> > nvme_common xhci_pci_renesas serio wmi
> > [16816.215451] CR2: 0000000000000080
> > [16816.215453] ---[ end trace 0000000000000000 ]---
> > [16816.215455] RIP: 0010:btree_node_free+0xf/0x160 [bcache]
> > [16816.215478] Code: 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90
> > 90 90
> > 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 55 53 48 89 fb 0f 1f
> > 44 00
> > 00 <48> 8b 83 80 00 00 00 48 8d ab 90 00 00 00 48 39 98 60 c3 00 00
> > 75
> > [16816.215480] RSP: 0018:ffffc90021777af8 EFLAGS: 00010207
> > [16816.215481] RAX: 0000000000000001 RBX: 0000000000000000 RCX:
> > ffff888515ce0670
> > [16816.215483] RDX: 0000000000000000 RSI: ffff888515ce0680 RDI:
> > 0000000000000000
> > [16816.215484] RBP: ffffc90021777bf0 R08: ffff88819476d9e0 R09:
> > 00000000013ffde8
> > [16816.215486] R10: 0000000000000000 R11: ffffc9000061b000 R12:
> > ffffc90021777e40
> > [16816.215487] R13: ffffc90021777bf0 R14: ffffc90021777bd8 R15:
> > ffff88819476c000
> > [16816.215488] FS:=C2=A0 0000000000000000(0000)
> > GS:ffff88886fdc0000(0000)
> > knlGS:0000000000000000
> > [16816.215490] CS:=C2=A0 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [16816.215492] CR2: 0000000000000080 CR3: 0000000294a20000 CR4:
> > 0000000000f50ee0
> > [16816.215493] PKRU: 55555554
> > [16816.215494] note: bcache_gc[83416] exited with irqs disabled
> >=20
> > 2. Kernel 6.1.55 (Debian 6.1.0-13) on HPE Gen11:
> >=20
> > [60654.670443] BUG: kernel NULL pointer dereference, address:
> > 0000000000000080
> > [60654.677474] #PF: supervisor read access in kernel mode
> > [60654.682651] #PF: error_code(0x0000) - not-present page
> > [60654.687825] PGD 0 [60654.689852] Oops: 0000 [#1] PREEMPT SMP
> > NOPTI
> > [60654.694240] CPU: 16 PID: 146330 Comm: bcache_gc Tainted:
> > G=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> > W=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 6.1.0-13-amd64 =
#1=C2=A0 Debian 6.1.55-1
> > [60654.704399] Hardware name: HPE ProLiant DL380 Gen11/ProLiant
> > DL380
> > Gen11, BIOS 1.48 10/19/2023
> > [60654.713071] RIP: 0010:btree_node_free+0xf/0x160 [bcache]
> > [60654.718437] Code: ff 48 89 d8 5b 5d 41 5c 41 5d c3 cc cc cc cc
> > 66 66
> > 2e 0f 1f 84 00 00 00 00 00 90 0f 1f 44 00 00 55 53 48 89 fb 0f 1f
> > 44 00
> > 00 <48> 8b 83 80 00 00 00 48 39 98 70 c3 00 00 0f 84 34 01 00 00 48
> > 8d
> > [60654.737342] RSP: 0018:ff77daed34cc3b18 EFLAGS: 00010207
> > [60654.742604] RAX: 0000000080000000 RBX: 0000000000000000 RCX:
> > 0000000000000000
> > [60654.749790] RDX: 0000000000000001 RSI: ff2971b8de800690 RDI:
> > 0000000000000000
> > [60654.756975] RBP: ff77daed34cc3c10 R08: ff2971d852dc65e0 R09:
> > ff2971b8de800000
> > [60654.764536] R10: 0000000000000000 R11: ff77daed34a4d000 R12:
> > ff77daed34cc3e60
> > [60654.771987] R13: ff77daed34cc3c10 R14: ff77daed34cc3c00 R15:
> > ff2971d851096400
> > [60654.779410] FS:=C2=A0 0000000000000000(0000)
> > GS:ff2971f7bf400000(0000)
> > knlGS:0000000000000000
> > [60654.787784] CS:=C2=A0 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [60654.793794] CR2: 0000000000000080 CR3: 0000000150610002 CR4:
> > 0000000000771ee0
> > [60654.801203] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> > 0000000000000000
> > [60654.808609] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7:
> > 0000000000000400
> > [60654.816009] PKRU: 55555554
> > [60654.818949] Call Trace:
> > [60654.821623]=C2=A0 <TASK>
> > [60654.823950]=C2=A0 ? __die_body.cold+0x1a/0x1f
> > [60654.828110]=C2=A0 ? page_fault_oops+0xd2/0x2b0
> > [60654.832352]=C2=A0 ? exc_page_fault+0x70/0x170
> > [60654.836505]=C2=A0 ? asm_exc_page_fault+0x22/0x30
> > [60654.840922]=C2=A0 ? btree_node_free+0xf/0x160 [bcache]
> > [60654.845863]=C2=A0 ? up_write+0x32/0x60
> > [60654.849396]=C2=A0 btree_gc_coalesce+0x2aa/0x890 [bcache]
> > [60654.854512]=C2=A0 ? bch_extent_bad+0x70/0x170 [bcache]
> > [60654.859452]=C2=A0 btree_gc_recurse+0x130/0x390 [bcache]
> > [60654.864475]=C2=A0 ? btree_gc_mark_node+0x72/0x230 [bcache]
> > [60654.869758]=C2=A0 bch_btree_gc+0x5da/0x600 [bcache]
> > [60654.874428]=C2=A0 ? cpuusage_read+0x10/0x10
> > [60654.878390]=C2=A0 ? bch_btree_gc+0x600/0x600 [bcache]
> > [60654.883232]=C2=A0 bch_gc_thread+0x135/0x180 [bcache]
> > [60654.887986]=C2=A0 ? cpuusage_read+0x10/0x10
> > [60654.891944]=C2=A0 kthread+0xe6/0x110
> > [60654.895290]=C2=A0 ? kthread_complete_and_exit+0x20/0x20
> > [60654.900296]=C2=A0 ret_from_fork+0x1f/0x30
> > [60654.904079]=C2=A0 </TASK>
> > [60654.906455] Modules linked in: bonding tls cfg80211 rfkill
> > intel_rapl_msr intel_rapl_common intel_uncore_frequency
> > intel_uncore_frequency_common i10nm_edac nfit binfmt_misc libnvdimm
> > x86_pkg_temp_thermal intel_powerclamp ipt_REJECT nf_reject_ipv4
> > coretemp
> > xt_comment nft_compat nf_tables nfnetlink nls_ascii nls_cp437
> > kvm_intel
> > vfat ipmi_ssif fat kvm irqbypass ghash_clmulni_intel sha512_ssse3
> > sha512_generic aesni_intel crypto_simd cryptd mgag200
> > drm_shmem_helper
> > pmt_telemetry pmt_crashlog rapl intel_cstate acpi_ipmi evdev
> > intel_sdsi
> > pmt_class idxd hpwdt mei_me isst_if_mbox_pci isst_if_mmio
> > drm_kms_helper
> > intel_uncore pcspkr isst_if_common mei watchdog hpilo i2c_algo_bit
> > ipmi_si idxd_bus acpi_tad intel_vsec sg acpi_power_meter button
> > ipmi_devintf ipmi_msghandler loop fuse efi_pstore drm configfs
> > efivarfs
> > ip_tables x_tables autofs4 ext4 crc16 mbcache jbd2 btrfs
> > blake2b_generic
> > xor raid6_pq zstd_compress libcrc32c crc32c_generic ses enclosure
> > bcache
> > sd_mod scsi_transport_sas dm_mod nvme
> > [60654.906508]=C2=A0 nvme_core xhci_pci t10_pi megaraid_sas ehci_pci
> > xhci_hcd
> > ehci_hcd crc64_rocksoft crc64 tg3 crc_t10dif scsi_mod usbcore
> > crct10dif_generic crc32_pclmul crc32c_intel crct10dif_pclmul libphy
> > scsi_common usb_common crct10dif_common wmi
> > [60655.017712] CR2: 0000000000000080
> > [60655.021262] ---[ end trace 0000000000000000 ]---
> > [60655.173744] RIP: 0010:btree_node_free+0xf/0x160 [bcache]
> > [60655.179337] Code: ff 48 89 d8 5b 5d 41 5c 41 5d c3 cc cc cc cc
> > 66 66
> > 2e 0f 1f 84 00 00 00 00 00 90 0f 1f 44 00 00 55 53 48 89 fb 0f 1f
> > 44 00
> > 00 <48> 8b 83 80 00 00 00 48 39 98 70 c3 00 00 0f 84 34 01 00 00 48
> > 8d
> > [60655.198649] RSP: 0018:ff77daed34cc3b18 EFLAGS: 00010207
> > [60655.204121] RAX: 0000000080000000 RBX: 0000000000000000 RCX:
> > 0000000000000000
> > [60655.211515] RDX: 0000000000000001 RSI: ff2971b8de800690 RDI:
> > 0000000000000000
> > [60655.218908] RBP: ff77daed34cc3c10 R08: ff2971d852dc65e0 R09:
> > ff2971b8de800000
> > [60655.226302] R10: 0000000000000000 R11: ff77daed34a4d000 R12:
> > ff77daed34cc3e60
> > [60655.233696] R13: ff77daed34cc3c10 R14: ff77daed34cc3c00 R15:
> > ff2971d851096400
> > [60655.241086] FS:=C2=A0 0000000000000000(0000)
> > GS:ff2971f7bf400000(0000)
> > knlGS:0000000000000000
> > [60655.249438] CS:=C2=A0 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [60655.255432] CR2: 0000000000000080 CR3: 0000000150610002 CR4:
> > 0000000000771ee0
> > [60655.262825] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> > 0000000000000000
> > [60655.270218] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7:
> > 0000000000000400
> > [60655.277607] PKRU: 55555554
> > [60655.280543] note: bcache_gc[146330] exited with irqs disabled
> >=20
> > Reproducer for us:
> >=20
> > dd if=3D/dev/zero of=3Dloop0 bs=3D1M count=3D1024
> > dd if=3D/dev/zero of=3Dloop1 bs=3D1M count=3D10240
> > losetup loop0 loop0
> > losetup loop1 loop1
> > make-bcache -C /dev/loop0 -B /dev/loop1 --writeback
> > mkfs.ext4 /dev/bcache0
> > mount /dev/bcache0 /mnt
> >=20
> > Then run fio with:
> >=20
> > [global]
> > bs=3D4k
> > ioengine=3Dlibaio
> > iodepth=3D4
> > size=3D8g
> > direct=3D1
> > runtime=3D60
> > directory=3D/mnt
> > filename=3Dssd.test.file
> >=20
> > [seq-write]
> > rw=3Dwrite
> > stonewall
> >=20
> > [rand-write]
> > rw=3Drandwrite
> > stonewall
> >=20
> > [seq-read]
> > rw=3Dread
> > stonewall
> >=20
> > [rand-read]
> > rw=3Drandread
> > stonewall
> >=20
> >=20
> > Cheers,
> > Stefan