Comment 0 for bug 1821913

This test has failed on T-4.4 i386. However I cannot reproduce this manually on 4.4.0-143 and 4.4.0-144

Maybe it can only be triggered with the whole test suite.

Invoking test aa9ddcd4b5557102fa25695c11904f249b4dec49

fix aa9ddcd4b5557102fa25695c11904f249b4dec49

Btrfs: do not use missing devices when showing devname

If you do the following

mkfs.btrfs /dev/sdb /dev/sdc
rmmod btrfs
dd if=/dev/zero of=/dev/sdb bs=1M count=1
mount -o degraded /dev/sdc /mnt/btrfs-test

the box will panic trying to deref the name for the missing dev since it is
the lower numbered devid. So fix show_devname to not use missing devices.

Found kernel issue:

[ 8658.778867] Invoking test aa9ddcd4b5557102fa25695c11904f249b4dec49
[ 8658.971180] BTRFS: device fsid dce6d13f-4906-4e33-a158-c30baef17d2e devid 1 transid 3 /dev/loop0
[ 8658.974670] BTRFS: device fsid dce6d13f-4906-4e33-a158-c30baef17d2e devid 2 transid 3 /dev/loop1
[ 8659.128467] =============================================================================
[ 8659.128488] BUG btrfs_extent_map (Not tainted): Objects remaining in btrfs_extent_map on kmem_cache_close()
[ 8659.128508] -----------------------------------------------------------------------------
[ 8659.128508]
[ 8659.128527] Disabling lock debugging due to kernel taint
[ 8659.128530] INFO: Slab 0xf73f44f8 objects=34 used=1 fp=0xec953618 flags=0x2800080
[ 8659.128547] CPU: 7 PID: 28009 Comm: rmmod Tainted: G B 4.4.0-144-generic #170~14.04.1-Ubuntu
[ 8659.128549] Hardware name: Dell Inc. PowerEdge R310/05XKKK, BIOS 1.8.2 08/17/2011
[ 8659.128551] 00000000 00000000 f4c55df8 c1391c03 f73f44f8 f4c55e18 f4c55e8c c11b53e2
[ 8659.128557] c19be8c0 f73f44f8 00000022 00000001 ec953618 02800080 656a624f 20737463
[ 8659.128562] 616d6572 6e696e69 6e692067 72746220 655f7366 6e657478 616d5f74 6e6f2070
[ 8659.128567] Call Trace:
[ 8659.128574] [] dump_stack+0x57/0x74
[ 8659.128580] [] slab_err+0x82/0xa0
[ 8659.128584] [] ? __kmalloc+0x1ed/0x220
[ 8659.128587] [] ? __free_slab+0x96/0x120
[ 8659.128590] [] ? arch_local_irq_disable+0x10/0x10
[ 8659.128593] [] ? __kmem_cache_shutdown+0xdb/0x220
[ 8659.128595] [] ? __kmem_cache_shutdown+0xdb/0x220
[ 8659.128598] [] __kmem_cache_shutdown+0x100/0x220
[ 8659.128601] [] ? kobj_kset_leave+0x3f/0x50
[ 8659.128604] [] ? sysfs_slab_remove+0x3c/0x40
[ 8659.128609] [] kmem_cache_destroy+0x14a/0x1a0
[ 8659.128613] [] ? _rcu_barrier+0x113/0x130
[ 8659.128643] [] extent_map_exit+0x16/0x20 [btrfs]
[ 8659.128665] [] exit_btrfs_fs+0x26/0xbc5 [btrfs]
[ 8659.128670] [] SyS_delete_module+0x171/0x1f0
[ 8659.128673] [] ? ____fput+0xd/0x10
[ 8659.128678] [] ? task_work_run+0x91/0xb0
[ 8659.128682] [] ? exit_to_usermode_loop+0x88/0x9c
[ 8659.128686] [] do_fast_syscall_32+0xa0/0x140
[ 8659.128691] [] sysenter_past_esp+0x3d/0x61
[ 8659.128696] INFO: Object 0xec953b40 @offset=2880
[ 8659.128708] kmem_cache_destroy btrfs_extent_map: Slab cache still has objects
[ 8659.128724] CPU: 7 PID: 28009 Comm: rmmod Tainted: G B 4.4.0-144-generic #170~14.04.1-Ubuntu
[ 8659.128726] Hardware name: Dell Inc. PowerEdge R310/05XKKK, BIOS 1.8.2 08/17/2011
[ 8659.128728] 00000000 00000000 f4c55ed8 c1391c03 f4d14480 f4c55ef8 f4c55f0c c118814b
[ 8659.128733] c19bceb8 ee4f37a0 c10ce793 00000001 f4c55ef0 f4c55ef0 f4c55ef8 f4c55ef8
[ 8659.128738] f8c40880 fffffff5 f4c54000 f4c55f14 f8bbcc06 f4c55f1c f8c28461 f4c55f78
[ 8659.128743] Call Trace:
[ 8659.128747] [] dump_stack+0x57/0x74
[ 8659.128751] [] kmem_cache_destroy+0x19b/0x1a0
[ 8659.128754] [] ? _rcu_barrier+0x113/0x130
[ 8659.128777] [] extent_map_exit+0x16/0x20 [btrfs]
[ 8659.128798] [] exit_btrfs_fs+0x26/0xbc5 [btrfs]
[ 8659.128801] [] SyS_delete_module+0x171/0x1f0
[ 8659.128804] [] ? ____fput+0xd/0x10
[ 8659.128807] [] ? task_work_run+0x91/0xb0
[ 8659.128810] [] ? exit_to_usermode_loop+0x88/0x9c
[ 8659.128813] [] do_fast_syscall_32+0xa0/0x140
[ 8659.128817] [] sysenter_past_esp+0x3d/0x61
[ 8659.280591] Btrfs loaded
[ 8659.347912] BTRFS: device fsid dce6d13f-4906-4e33-a158-c30baef17d2e devid 2 transid 4 /dev/loop1
[ 8659.372352] BTRFS info (device loop1): allowing degraded mounts
[ 8659.372359] BTRFS info (device loop1): disk space caching is enabled
[ 8659.374761] BTRFS warning (device loop1): devid 1 uuid 61157fd6-f333-4bf7-8938-999393075c2f is missing
[ 8659.374799] BTRFS: failed to read chunk root on loop1
[ 8659.391940] BTRFS: open_ctree failed
[ 8659.475622] Test aa9ddcd4b5557102fa25695c11904f249b4dec49 returned 0

FAIL: aa9ddcd4b5557102fa25695c11904f249b4dec49 (ret=1)