On Fri, Feb 16, 2018 at 07:51:38PM +0000, Dmitriy Gorokh wrote:
> On detaching of a disk which is a part of a RAID6 filesystem, the following 
> kernel OOPS may happen:
> 
> [63122.680461] BTRFS error (device sdo): bdev /dev/sdo errs: wr 0, rd 0, 
> flush 1, corrupt 0, gen 0 
> [63122.719584] BTRFS warning (device sdo): lost page write due to IO error on 
> /dev/sdo 
> [63122.719587] BTRFS error (device sdo): bdev /dev/sdo errs: wr 1, rd 0, 
> flush 1, corrupt 0, gen 0 
> [63122.803516] BTRFS warning (device sdo): lost page write due to IO error on 
> /dev/sdo 
> [63122.803519] BTRFS error (device sdo): bdev /dev/sdo errs: wr 2, rd 0, 
> flush 1, corrupt 0, gen 0 
> [63122.863902] BTRFS critical (device sdo): fatal error on device /dev/sdo 
> [63122.935338] BUG: unable to handle kernel NULL pointer dereference at 
> 0000000000000080 
> [63122.946554] IP: fail_bio_stripe+0x58/0xa0 [btrfs] 
> [63122.958185] PGD 9ecda067 P4D 9ecda067 PUD b2b37067 PMD 0 
> [63122.971202] Oops: 0000 [#1] SMP 
> [63122.990786] Modules linked in: libcrc32c dlm configfs cpufreq_userspace 
> cpufreq_powersave cpufreq_conservative softdog nfsd auth_rpcgss nfs_acl nfs 
> lockd grace fscache sunrpc bonding ipmi_devintf ipmi_msghandler joydev 
> snd_intel8x0 snd_ac97_codec snd_pcm snd_timer snd psmouse evdev parport_pc 
> soundcore serio_raw battery pcspkr video ac97_bus ac parport ohci_pci 
> ohci_hcd i2c_piix4 button crc32c_generic crc32c_intel btrfs xor 
> zstd_decompress zstd_compress xxhash raid6_pq dm_mod dax raid1 md_mod 
> hid_generic usbhid hid xhci_pci xhci_hcd ehci_pci ehci_hcd usbcore sg sd_mod 
> sr_mod cdrom ata_generic ahci libahci ata_piix libata e1000 scsi_mod [last 
> unloaded: scst] 
> [63123.006760] CPU: 0 PID: 3979 Comm: kworker/u8:9 Tainted: G W 
> 4.14.2-16-scst34x+ #8 
> [63123.007091] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS 
> VirtualBox 12/01/2006 
> [63123.007402] Workqueue: btrfs-worker btrfs_worker_helper [btrfs] 
> [63123.007595] task: ffff880036ea4040 task.stack: ffffc90006384000 
> [63123.007796] RIP: 0010:fail_bio_stripe+0x58/0xa0 [btrfs] 
> [63123.007968] RSP: 0018:ffffc90006387ad8 EFLAGS: 00010287 
> [63123.008140] RAX: 0000000000000002 RBX: ffff88004beaa0b8 RCX: 
> ffff8800b2bd5690 
> [63123.008359] RDX: 0000000000000000 RSI: ffff88007bb43500 RDI: 
> ffff88004beaa000 
> [63123.008621] RBP: ffffc90006387ae8 R08: 0000000099100000 R09: 
> ffff8800b2bd5600 
> [63123.008840] R10: 0000000000000004 R11: 0000000000010000 R12: 
> ffff88007bb43500 
> [63123.009059] R13: 00000000fffffffb R14: ffff880036fc5180 R15: 
> 0000000000000004 
> [63123.009278] FS: 0000000000000000(0000) GS:ffff8800b7000000(0000) 
> knlGS:0000000000000000 
> [63123.009564] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
> [63123.009748] CR2: 0000000000000080 CR3: 00000000b0866000 CR4: 
> 00000000000406f0 
> [63123.009969] Call Trace: 
> [63123.010085] raid_write_end_io+0x7e/0x80 [btrfs] 
> [63123.010251] bio_endio+0xa1/0x120 
> [63123.010378] generic_make_request+0x218/0x270 
> [63123.010921] submit_bio+0x66/0x130 
> [63123.011073] finish_rmw+0x3fc/0x5b0 [btrfs] 
> [63123.011245] full_stripe_write+0x96/0xc0 [btrfs] 
> [63123.011428] raid56_parity_write+0x117/0x170 [btrfs] 
> [63123.011604] btrfs_map_bio+0x2ec/0x320 [btrfs] 
> [63123.011759] ? ___cache_free+0x1c5/0x300 
> [63123.011909] __btrfs_submit_bio_done+0x26/0x50 [btrfs] 
> [63123.012087] run_one_async_done+0x9c/0xc0 [btrfs] 
> [63123.012257] normal_work_helper+0x19e/0x300 [btrfs] 
> [63123.012429] btrfs_worker_helper+0x12/0x20 [btrfs] 
> [63123.012656] process_one_work+0x14d/0x350 
> [63123.012888] worker_thread+0x4d/0x3a0 
> [63123.013026] ? _raw_spin_unlock_irqrestore+0x15/0x20 
> [63123.013192] kthread+0x109/0x140 
> [63123.013315] ? process_scheduled_works+0x40/0x40 
> [63123.013472] ? kthread_stop+0x110/0x110 
> [63123.013610] ret_from_fork+0x25/0x30 
> [63123.013741] Code: 7e 43 31 c0 48 63 d0 48 8d 14 52 49 8d 4c d1 60 48 8b 51 
> 08 49 39 d0 72 1f 4c 63 1b 4c 01 da 49 39 d0 73 14 48 8b 11 48 8b 52 68 <48> 
> 8b 8a 80 00 00 00 48 39 4e 08 74 14 83 c0 01 44 39 d0 75 c4 
> [63123.014469] RIP: fail_bio_stripe+0x58/0xa0 [btrfs] RSP: ffffc90006387ad8 
> [63123.014678] CR2: 0000000000000080 
> [63123.016590] ---[ end trace a295ea7259c17880 ]— 
> 
> This is reproducible in a cycle, where a series of writes is followed by SCSI 
> device delete command. The test may take up to few minutes.
> 
> Fixes: commit 74d46992e0d9dee7f1f376de0d56d31614c8a17a ("block: replace 
> bi_bdev with a gendisk pointer and partitions index")

Right, the commit introduced dereference of stripe->dev->bdev so we have
to check it first.

Please update the Fixes: tag, the word 'commit' should not be there and
the sha1 length can be shortened to 12 digits.

Also please add your Signed-off-by. Thanks.
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