5.5.0-0.rc1 hang, could be zstd compression related

5.5.0-0.rc1 hang, could be zstd compression related

[Chris Murphy]

Could continue to chat in one application, the desktop environment was
responsive, but no shells worked and I couldn't get to a tty and I
couldn't ssh into remotely. Looks like the journal has everything up
until I pressed and held down the power button.


/dev/nvme0n1p7 on / type btrfs
(rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=274,subvol=/root)

dmesg pretty
https://pastebin.com/pvG3ERnd

dmesg (likely MUA stomped)
[10224.184137] flap.local kernel: perf: interrupt took too long (2522
> 2500), lowering kernel.perf_event_max_sample_rate to 79000
[14712.698184] flap.local kernel: perf: interrupt took too long (3153
> 3152), lowering kernel.perf_event_max_sample_rate to 63000
[17903.211976] flap.local kernel: Lockdown: systemd-logind:
hibernation is restricted; see man kernel_lockdown.7
[22877.667177] flap.local kernel: BUG: kernel NULL pointer
dereference, address: 00000000000006c8
[22877.667182] flap.local kernel: #PF: supervisor read access in kernel mode
[22877.667184] flap.local kernel: #PF: error_code(0x0000) - not-present page
[22877.667187] flap.local kernel: PGD 0 P4D 0
[22877.667191] flap.local kernel: Oops: 0000 [#1] SMP PTI
[22877.667194] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
Not tainted 5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
[22877.667196] flap.local kernel: Hardware name: HP HP Spectre
Notebook/81A0, BIOS F.43 04/16/2019
[22877.667226] flap.local kernel: Workqueue: btrfs-delalloc
btrfs_work_helper [btrfs]
[22877.667233] flap.local kernel: RIP:
0010:bio_associate_blkg_from_css+0x1c/0x3b0
[22877.667235] flap.local kernel: Code: 66 89 6b 14 c7 43 1c 01 00 00
00 5b 5d c3 0f 1f 44 00 00 41 55 41 54 49 89 f4 55 48 89 fd 53 48 8b
47 08 65 ff 05 ac 6f ab 7d <4c> 8b a8 c8 06 00 00 68 85 3e 56 82 31 f6
45 31 c9 45 31 c0 b9 02
[22877.667238] flap.local kernel: RSP: 0018:ffff971181fcfca8 EFLAGS: 00010282
[22877.667240] flap.local kernel: RAX: 0000000000000000 RBX:
ffff8b76697cd3c0 RCX: 0000000000000000
[22877.667243] flap.local kernel: RDX: 000000000000c000 RSI:
ffff8b73eeabc800 RDI: ffff8b76385055b0
[22877.667245] flap.local kernel: RBP: ffff8b76385055b0 R08:
ffff8b76385055b0 R09: ffff8b7634800900
[22877.667247] flap.local kernel: R10: 00000000001f5c60 R11:
0000000000000000 R12: ffff8b73eeabc800
[22877.667249] flap.local kernel: R13: ffff8b75fbbc2808 R14:
ffff8b766b000000 R15: ffff8b76385055b0
[22877.667251] flap.local kernel: FS:  0000000000000000(0000)
GS:ffff8b7676a00000(0000) knlGS:0000000000000000
[22877.667254] flap.local kernel: CS:  0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[22877.667256] flap.local kernel: CR2: 00000000000006c8 CR3:
0000000009612001 CR4: 00000000003606e0
[22877.667257] flap.local kernel: Call Trace:
[22877.667287] flap.local kernel:
btrfs_submit_compressed_write+0x117/0x360 [btrfs]
[22877.667310] flap.local kernel:  submit_compressed_extents+0x315/0x460 [btrfs]
[22877.667317] flap.local kernel:  ? find_held_lock+0x32/0x90
[22877.667321] flap.local kernel:  ? mark_held_locks+0x2d/0x80
[22877.667345] flap.local kernel:  btrfs_work_helper+0x148/0x5b0 [btrfs]
[22877.667352] flap.local kernel:  process_one_work+0x272/0x5a0
[22877.667359] flap.local kernel:  worker_thread+0x50/0x3b0
[22877.667365] flap.local kernel:  kthread+0x106/0x140
[22877.667368] flap.local kernel:  ? process_one_work+0x5a0/0x5a0
[22877.667371] flap.local kernel:  ? kthread_park+0x90/0x90
[22877.667376] flap.local kernel:  ret_from_fork+0x3a/0x50
[22877.667384] flap.local kernel: Modules linked in: hidp thunderbolt
uinput rfcomm ccm xt_CHECKSUM xt_MASQUERADE nf_nat_tftp
nf_conntrack_tftp tun bridge stp llc nf_conntrack_netbios_ns
nf_conntrack_broadcast xt_CT ip6t_REJECT nf_reject_ipv6 ip6t_rpfilter
ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute
ip6table_nat ip6table_mangle ip6table_raw ip6table_security
iptable_nat nf_nat iptable_mangle iptable_raw iptable_security
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink
ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter cmac
bnep x86_pkg_temp_thermal intel_powerclamp coretemp sunrpc kvm
snd_soc_skl iwlmvm snd_soc_hdac_hda mac80211 snd_hda_ext_core
snd_soc_sst_ipc snd_soc_sst_dsp snd_soc_acpi_intel_match snd_soc_acpi
libarc4 iTCO_wdt iTCO_vendor_support mei_hdcp intel_rapl_msr iwlwifi
uvcvideo snd_hda_codec_hdmi irqbypass snd_soc_core
snd_hda_codec_conexant vfat snd_compress snd_hda_codec_generic
ac97_bus crct10dif_pclmul ledtrig_audio fat videobuf2_vmalloc
[22877.667461] flap.local kernel: CR2: 00000000000006c8
[22877.667464] flap.local kernel: ---[ end trace 833e6c4636dfc480 ]---
[22877.667468] flap.local kernel: RIP:
0010:bio_associate_blkg_from_css+0x1c/0x3b0
[22877.667471] flap.local kernel: Code: 66 89 6b 14 c7 43 1c 01 00 00
00 5b 5d c3 0f 1f 44 00 00 41 55 41 54 49 89 f4 55 48 89 fd 53 48 8b
47 08 65 ff 05 ac 6f ab 7d <4c> 8b a8 c8 06 00 00 68 85 3e 56 82 31 f6
45 31 c9 45 31 c0 b9 02
[22877.667473] flap.local kernel: RSP: 0018:ffff971181fcfca8 EFLAGS: 00010282
[22877.667475] flap.local kernel: RAX: 0000000000000000 RBX:
ffff8b76697cd3c0 RCX: 0000000000000000
[22877.667477] flap.local kernel: RDX: 000000000000c000 RSI:
ffff8b73eeabc800 RDI: ffff8b76385055b0
[22877.667479] flap.local kernel: RBP: ffff8b76385055b0 R08:
ffff8b76385055b0 R09: ffff8b7634800900
[22877.667481] flap.local kernel: R10: 00000000001f5c60 R11:
0000000000000000 R12: ffff8b73eeabc800
[22877.667483] flap.local kernel: R13: ffff8b75fbbc2808 R14:
ffff8b766b000000 R15: ffff8b76385055b0
[22877.667485] flap.local kernel: FS:  0000000000000000(0000)
GS:ffff8b7676a00000(0000) knlGS:0000000000000000
[22877.667487] flap.local kernel: CS:  0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[22877.667490] flap.local kernel: CR2: 00000000000006c8 CR3:
0000000009612001 CR4: 00000000003606e0
[22877.667493] flap.local kernel: BUG: sleeping function called from
invalid context at include/linux/percpu-rwsem.h:38
[22877.667496] flap.local kernel: in_atomic(): 1, irqs_disabled(): 1,
non_block: 0, pid: 14747, name: kworker/u8:7
[22877.667498] flap.local kernel: INFO: lockdep is turned off.
[22877.667500] flap.local kernel: irq event stamp: 136012
[22877.667504] flap.local kernel: hardirqs last  enabled at (136011):
[<ffffffff822b8e66>] __test_set_page_writeback+0x2c6/0x4e0
[22877.667509] flap.local kernel: hardirqs last disabled at (136012):
[<ffffffff820038d7>] trace_hardirqs_off_thunk+0x1a/0x1c
[22877.667532] flap.local kernel: softirqs last  enabled at (135852):
[<ffffffffc098c2a2>] zstd_put_workspace+0x82/0x160 [btrfs]
[22877.667553] flap.local kernel: softirqs last disabled at (135850):
[<ffffffffc098c23a>] zstd_put_workspace+0x1a/0x160 [btrfs]
[22877.667557] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
Tainted: G      D           5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
[22877.667559] flap.local kernel: Hardware name: HP HP Spectre
Notebook/81A0, BIOS F.43 04/16/2019
[22877.667580] flap.local kernel: Workqueue: btrfs-delalloc
btrfs_work_helper [btrfs]
[22877.667582] flap.local kernel: Call Trace:
[22877.667587] flap.local kernel:  dump_stack+0x8f/0xd0
[22877.667592] flap.local kernel:  ___might_sleep.cold+0xb3/0xc3
[22877.667596] flap.local kernel:  exit_signals+0x30/0x2d0
[22877.667600] flap.local kernel:  do_exit+0xc1/0xcd0
[22877.667605] flap.local kernel:  ? kthread+0x106/0x140
[22877.667610] flap.local kernel:  rewind_stack_do_exit+0x17/0x20
[22877.667618] flap.local kernel: note: kworker/u8:7[14747] exited
with preempt_count 1
[23112.137098] flap.local kernel: psmouse serio1: TouchPad at
isa0060/serio1/input0 lost sync at byte 1
[23112.138141] flap.local kernel: psmouse serio1: TouchPad at
isa0060/serio1/input0 lost sync at byte 1
[23112.139241] flap.local kernel: psmouse serio1: TouchPad at
isa0060/serio1/input0 lost sync at byte 1
[23112.140272] flap.local kernel: psmouse serio1: TouchPad at
isa0060/serio1/input0 lost sync at byte 1
[23112.151582] flap.local kernel: psmouse serio1: TouchPad at
isa0060/serio1/input0 - driver resynced.
[24074.296721] flap.local kernel: perf: interrupt took too long (3944
> 3941), lowering kernel.perf_event_max_sample_rate to 50000
[25580.723981] flap.local kernel: Lockdown: systemd-logind:
hibernation is restricted; see man kernel_lockdown.7
[25589.124775] flap.local kernel: hp_wmi: Unknown event_id - 131073 - 0x0
[chris@flap ~]$


dmesg full
https://drive.google.com/open?id=1mZlSn0N6rVwLpr42EtQbF1qrggQ0ygfF




-- 
Chris Murphy

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[Chris Murphy]

OK this is interesting. It took 7 hours to hit it the first time. And
the consistent reproducer I've now run into twice, is 'dnf install'
any little rpm, which is what I was doing the first time I hit it. I'm
not sure what about dnf or rpm is triggering this,  I've got other
things doing a bunch of small file writes including Firefox - yet
those don't trigger it.

Next, I tried a couple more times with compression disabled, and the
problem doesn't happen. So it does seem zstd related. Maybe.


Chris Murphy

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[Josef Bacik]

On 12/10/19 11:00 PM, Chris Murphy wrote:
> Could continue to chat in one application, the desktop environment was
> responsive, but no shells worked and I couldn't get to a tty and I
> couldn't ssh into remotely. Looks like the journal has everything up
> until I pressed and held down the power button.
> 
> 
> /dev/nvme0n1p7 on / type btrfs
> (rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=274,subvol=/root)
> 
> dmesg pretty
> https://pastebin.com/pvG3ERnd
> 
> dmesg (likely MUA stomped)
> [10224.184137] flap.local kernel: perf: interrupt took too long (2522
>> 2500), lowering kernel.perf_event_max_sample_rate to 79000
> [14712.698184] flap.local kernel: perf: interrupt took too long (3153
>> 3152), lowering kernel.perf_event_max_sample_rate to 63000
> [17903.211976] flap.local kernel: Lockdown: systemd-logind:
> hibernation is restricted; see man kernel_lockdown.7
> [22877.667177] flap.local kernel: BUG: kernel NULL pointer
> dereference, address: 00000000000006c8
> [22877.667182] flap.local kernel: #PF: supervisor read access in kernel mode
> [22877.667184] flap.local kernel: #PF: error_code(0x0000) - not-present page
> [22877.667187] flap.local kernel: PGD 0 P4D 0
> [22877.667191] flap.local kernel: Oops: 0000 [#1] SMP PTI
> [22877.667194] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
> Not tainted 5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
> [22877.667196] flap.local kernel: Hardware name: HP HP Spectre
> Notebook/81A0, BIOS F.43 04/16/2019
> [22877.667226] flap.local kernel: Workqueue: btrfs-delalloc
> btrfs_work_helper [btrfs]
> [22877.667233] flap.local kernel: RIP:
> 0010:bio_associate_blkg_from_css+0x1c/0x3b0

This looks like the extent_map bdev cleanup thing that was supposed to be fixed, 
did you send the patch without the fix for it Dave?  Thanks,

Josef

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[David Sterba]

On Wed, Dec 11, 2019 at 09:58:45AM -0500, Josef Bacik wrote:
> On 12/10/19 11:00 PM, Chris Murphy wrote:
> > Could continue to chat in one application, the desktop environment was
> > responsive, but no shells worked and I couldn't get to a tty and I
> > couldn't ssh into remotely. Looks like the journal has everything up
> > until I pressed and held down the power button.
> > 
> > 
> > /dev/nvme0n1p7 on / type btrfs
> > (rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=274,subvol=/root)
> > 
> > dmesg pretty
> > https://pastebin.com/pvG3ERnd
> > 
> > dmesg (likely MUA stomped)
> > [10224.184137] flap.local kernel: perf: interrupt took too long (2522
> >> 2500), lowering kernel.perf_event_max_sample_rate to 79000
> > [14712.698184] flap.local kernel: perf: interrupt took too long (3153
> >> 3152), lowering kernel.perf_event_max_sample_rate to 63000
> > [17903.211976] flap.local kernel: Lockdown: systemd-logind:
> > hibernation is restricted; see man kernel_lockdown.7
> > [22877.667177] flap.local kernel: BUG: kernel NULL pointer
> > dereference, address: 00000000000006c8
> > [22877.667182] flap.local kernel: #PF: supervisor read access in kernel mode
> > [22877.667184] flap.local kernel: #PF: error_code(0x0000) - not-present page
> > [22877.667187] flap.local kernel: PGD 0 P4D 0
> > [22877.667191] flap.local kernel: Oops: 0000 [#1] SMP PTI
> > [22877.667194] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
> > Not tainted 5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
> > [22877.667196] flap.local kernel: Hardware name: HP HP Spectre
> > Notebook/81A0, BIOS F.43 04/16/2019
> > [22877.667226] flap.local kernel: Workqueue: btrfs-delalloc
> > btrfs_work_helper [btrfs]
> > [22877.667233] flap.local kernel: RIP:
> > 0010:bio_associate_blkg_from_css+0x1c/0x3b0
> 
> This looks like the extent_map bdev cleanup thing that was supposed to be fixed, 
> did you send the patch without the fix for it Dave?  Thanks,

The fix for NULL bdev was added in 429aebc0a9a063667dba21 (and tested
with cgroups v2) and it's in a different function than the one that
appears on the stacktrace.

This seems to be another instance where the bdev is needed right after
the bio is created but way earlier than it's actually known for real,
yet still needed for the blkcg thing.

 443         bio = btrfs_bio_alloc(first_byte);
 444         bio->bi_opf = REQ_OP_WRITE | write_flags;
 445         bio->bi_private = cb;
 446         bio->bi_end_io = end_compressed_bio_write;
 447
 448         if (blkcg_css) {
 449                 bio->bi_opf |= REQ_CGROUP_PUNT;
 450                 bio_associate_blkg_from_css(bio, blkcg_css);
 451         }

Strange that it takes so long to reproduce, meaning the 'if' branch is
not taken often.

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[David Sterba]

On Wed, Dec 11, 2019 at 04:55:53PM +0100, David Sterba wrote:
> On Wed, Dec 11, 2019 at 09:58:45AM -0500, Josef Bacik wrote:
> > On 12/10/19 11:00 PM, Chris Murphy wrote:
> > > Could continue to chat in one application, the desktop environment was
> > > responsive, but no shells worked and I couldn't get to a tty and I
> > > couldn't ssh into remotely. Looks like the journal has everything up
> > > until I pressed and held down the power button.
> > > 
> > > 
> > > /dev/nvme0n1p7 on / type btrfs
> > > (rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=274,subvol=/root)
> > > 
> > > dmesg pretty
> > > https://pastebin.com/pvG3ERnd
> > > 
> > > dmesg (likely MUA stomped)
> > > [10224.184137] flap.local kernel: perf: interrupt took too long (2522
> > >> 2500), lowering kernel.perf_event_max_sample_rate to 79000
> > > [14712.698184] flap.local kernel: perf: interrupt took too long (3153
> > >> 3152), lowering kernel.perf_event_max_sample_rate to 63000
> > > [17903.211976] flap.local kernel: Lockdown: systemd-logind:
> > > hibernation is restricted; see man kernel_lockdown.7
> > > [22877.667177] flap.local kernel: BUG: kernel NULL pointer
> > > dereference, address: 00000000000006c8
> > > [22877.667182] flap.local kernel: #PF: supervisor read access in kernel mode
> > > [22877.667184] flap.local kernel: #PF: error_code(0x0000) - not-present page
> > > [22877.667187] flap.local kernel: PGD 0 P4D 0
> > > [22877.667191] flap.local kernel: Oops: 0000 [#1] SMP PTI
> > > [22877.667194] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
> > > Not tainted 5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
> > > [22877.667196] flap.local kernel: Hardware name: HP HP Spectre
> > > Notebook/81A0, BIOS F.43 04/16/2019
> > > [22877.667226] flap.local kernel: Workqueue: btrfs-delalloc
> > > btrfs_work_helper [btrfs]
> > > [22877.667233] flap.local kernel: RIP:
> > > 0010:bio_associate_blkg_from_css+0x1c/0x3b0
> > 
> > This looks like the extent_map bdev cleanup thing that was supposed to be fixed, 
> > did you send the patch without the fix for it Dave?  Thanks,
> 
> The fix for NULL bdev was added in 429aebc0a9a063667dba21 (and tested
> with cgroups v2) and it's in a different function than the one that
> appears on the stacktrace.
> 
> This seems to be another instance where the bdev is needed right after
> the bio is created but way earlier than it's actually known for real,
> yet still needed for the blkcg thing.
> 
>  443         bio = btrfs_bio_alloc(first_byte);
>  444         bio->bi_opf = REQ_OP_WRITE | write_flags;
>  445         bio->bi_private = cb;
>  446         bio->bi_end_io = end_compressed_bio_write;
>  447
>  448         if (blkcg_css) {
>  449                 bio->bi_opf |= REQ_CGROUP_PUNT;
>  450                 bio_associate_blkg_from_css(bio, blkcg_css);
>  451         }
> 
> Strange that it takes so long to reproduce, meaning the 'if' branch is
> not taken often.

Compile tested only:

--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -446,6 +446,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
        bio->bi_end_io = end_compressed_bio_write;
 
        if (blkcg_css) {
+               bio_set_bev(bio, fs_info->fs_devices->latest_bdev);
                bio->bi_opf |= REQ_CGROUP_PUNT;
                bio_associate_blkg_from_css(bio, blkcg_css);
        }

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[Chris Murphy]

Applied that single line on top of 5.5.0-rc3

fs/btrfs/compression.c:449:17: error: implicit declaration of function
‘bio_set_bev’; did you mean ‘bio_set_dev’?
[-Werror=implicit-function-declaration]

If I use bio_set_dev

...
  CC [M]  fs/btrfs/compression.o
fs/btrfs/compression.o: warning: objtool:
end_compressed_bio_read.cold()+0x11: unreachable instruction
  LD [M]  fs/btrfs/btrfs.o
  GEN     .version
...

Despite that, it seems to work, and no crash with the reproducer.

On Wed, Dec 11, 2019 at 8:59 AM David Sterba <dsterba@suse.cz> wrote:
>
> On Wed, Dec 11, 2019 at 04:55:53PM +0100, David Sterba wrote:
> > On Wed, Dec 11, 2019 at 09:58:45AM -0500, Josef Bacik wrote:
> > > On 12/10/19 11:00 PM, Chris Murphy wrote:
> > > > Could continue to chat in one application, the desktop environment was
> > > > responsive, but no shells worked and I couldn't get to a tty and I
> > > > couldn't ssh into remotely. Looks like the journal has everything up
> > > > until I pressed and held down the power button.
> > > >
> > > >
> > > > /dev/nvme0n1p7 on / type btrfs
> > > > (rw,noatime,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=274,subvol=/root)
> > > >
> > > > dmesg pretty
> > > > https://pastebin.com/pvG3ERnd
> > > >
> > > > dmesg (likely MUA stomped)
> > > > [10224.184137] flap.local kernel: perf: interrupt took too long (2522
> > > >> 2500), lowering kernel.perf_event_max_sample_rate to 79000
> > > > [14712.698184] flap.local kernel: perf: interrupt took too long (3153
> > > >> 3152), lowering kernel.perf_event_max_sample_rate to 63000
> > > > [17903.211976] flap.local kernel: Lockdown: systemd-logind:
> > > > hibernation is restricted; see man kernel_lockdown.7
> > > > [22877.667177] flap.local kernel: BUG: kernel NULL pointer
> > > > dereference, address: 00000000000006c8
> > > > [22877.667182] flap.local kernel: #PF: supervisor read access in kernel mode
> > > > [22877.667184] flap.local kernel: #PF: error_code(0x0000) - not-present page
> > > > [22877.667187] flap.local kernel: PGD 0 P4D 0
> > > > [22877.667191] flap.local kernel: Oops: 0000 [#1] SMP PTI
> > > > [22877.667194] flap.local kernel: CPU: 2 PID: 14747 Comm: kworker/u8:7
> > > > Not tainted 5.5.0-0.rc1.git0.1.fc32.x86_64+debug #1
> > > > [22877.667196] flap.local kernel: Hardware name: HP HP Spectre
> > > > Notebook/81A0, BIOS F.43 04/16/2019
> > > > [22877.667226] flap.local kernel: Workqueue: btrfs-delalloc
> > > > btrfs_work_helper [btrfs]
> > > > [22877.667233] flap.local kernel: RIP:
> > > > 0010:bio_associate_blkg_from_css+0x1c/0x3b0
> > >
> > > This looks like the extent_map bdev cleanup thing that was supposed to be fixed,
> > > did you send the patch without the fix for it Dave?  Thanks,
> >
> > The fix for NULL bdev was added in 429aebc0a9a063667dba21 (and tested
> > with cgroups v2) and it's in a different function than the one that
> > appears on the stacktrace.
> >
> > This seems to be another instance where the bdev is needed right after
> > the bio is created but way earlier than it's actually known for real,
> > yet still needed for the blkcg thing.
> >
> >  443         bio = btrfs_bio_alloc(first_byte);
> >  444         bio->bi_opf = REQ_OP_WRITE | write_flags;
> >  445         bio->bi_private = cb;
> >  446         bio->bi_end_io = end_compressed_bio_write;
> >  447
> >  448         if (blkcg_css) {
> >  449                 bio->bi_opf |= REQ_CGROUP_PUNT;
> >  450                 bio_associate_blkg_from_css(bio, blkcg_css);
> >  451         }
> >
> > Strange that it takes so long to reproduce, meaning the 'if' branch is
> > not taken often.
>
> Compile tested only:
>
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -446,6 +446,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>         bio->bi_end_io = end_compressed_bio_write;
>
>         if (blkcg_css) {
> +               bio_set_bev(bio, fs_info->fs_devices->latest_bdev);
>                 bio->bi_opf |= REQ_CGROUP_PUNT;
>                 bio_associate_blkg_from_css(bio, blkcg_css);
>         }
>


-- 
Chris Murphy

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[Chris Murphy]

BTW, I hit this with lzo too, so it's not zstd specific.

--
Chris Murphy

Re: 5.5.0-0.rc1 hang, could be zstd compression related

[David Sterba]

On Fri, Jan 03, 2020 at 01:26:08AM -0700, Chris Murphy wrote:
> BTW, I hit this with lzo too, so it's not zstd specific.

That's correct and the fix is going to appear in the next -rc.