When executing btrfs/126 test on kdave/for-next branch on a ppc64 guest, I
noticed the following call trace.
[ 77.335887] ------------[ cut here ]------------
[ 77.336115] WARNING: CPU: 0 PID: 8325 at /root/repos/linux/fs/btrfs/qgroup.c:2443 .btrfs_qgroup_free_refroot+0x188/0x220
[ 77.336303] Modules linked in:
[ 77.336393] CPU: 0 PID: 8325 Comm: umount Not tainted 4.9.0-rc5-00062-g6b74e43 #22
[ 77.336526] task: c00000062b8d4880 task.stack: c00000062b9a4000
[ 77.336638] NIP: c0000000005cf018 LR: c0000000005ceff8 CTR: c0000000005390c0
[ 77.336771] REGS: c00000062b9a7450 TRAP: 0700 Not tainted (4.9.0-rc5-00062-g6b74e43)
[ 77.336908] MSR: 800000000282b032
[ 77.336960] <
[ 77.337027] SF
[ 77.337053] ,VEC
[ 77.337087] ,VSX
[ 77.337114] ,EE
[ 77.337146] ,FP
[ 77.337173] ,ME
[ 77.337207] ,IR
[ 77.337233] ,DR
[ 77.337267] ,RI
[ 77.337294] >
[ 77.337330] CR: 88000842 XER: 00000000
[ 77.337392] CFAR: c0000000005c9b5c
[ 77.337443] SOFTE: 1
[ 77.337477]
GPR00:
[ 77.337517] c0000000005cefcc
[ 77.337575] c00000062b9a76d0
[ 77.337626] c000000001103a00
[ 77.337714] c00000063e058d40
[ 77.337765]
GPR04:
[ 77.337817] c00000062b9a7740
[ 77.337868] 0000000000000008
[ 77.337927] 000000000005f000
[ 77.337978] 000000063eed0000
[ 77.338037]
GPR08:
[ 77.338080] c00000062f9629c8
[ 77.338138] 0000000000000001
[ 77.338191] fffffffffffff000
[ 77.338248] c00000063e058e80
[ 77.338300]
GPR12:
[ 77.338384] 0000000000000000
[ 77.338435] c00000000fe00000
[ 77.338498] 0000000020000000
[ 77.338548] 0000000000000000
[ 77.338605]
GPR16:
[ 77.338645] 0000000000000008
[ 77.338703] 000000004d5906fc
[ 77.338754] 000000004d5a6c08
[ 77.338811] 000000004d54b3d0
[ 77.338866]
GPR20:
[ 77.338921] 000001000bcf8440
[ 77.338972] 0000000000000000
[ 77.339030] 0000000000000000
[ 77.339080] c00000062523b078
[ 77.339138]
GPR24:
[ 77.339178] c00000062523b080
[ 77.339240] c000000000da2b58
[ 77.339290] 0000000000000000
[ 77.339347] c00000062e539600
[ 77.339398]
GPR28:
[ 77.339485] 0000000000060000
[ 77.339536] c00000062523b000
[ 77.339594] c00000062e539600
[ 77.339644] c00000062e539688
[ 77.339740] NIP [c0000000005cf018] .btrfs_qgroup_free_refroot+0x188/0x220
[ 77.339852] LR [c0000000005ceff8] .btrfs_qgroup_free_refroot+0x168/0x220
[ 77.339959] Call Trace:
[ 77.339998] [c00000062b9a76d0] [c0000000005cefcc] .btrfs_qgroup_free_refroot+0x13c/0x220
[ 77.340123] (unreliable)
[ 77.340193] [c00000062b9a7790] [c00000000054210c] .commit_fs_roots+0x19c/0x240
[ 77.340355] [c00000062b9a78a0] [c0000000005451a0] .btrfs_commit_transaction.part.5+0x480/0xbe0
[ 77.340554] [c00000062b9a7970] [c000000000503bd4] .btrfs_sync_fs+0x74/0x1c0
[ 77.340725] [c00000062b9a7a10] [c0000000002d6ce0] .sync_filesystem+0xd0/0x100
[ 77.340891] [c00000062b9a7a90] [c000000000294f88] .generic_shutdown_super+0x38/0x1a0
[ 77.341052] [c00000062b9a7b10] [c000000000295508] .kill_anon_super+0x18/0x30
[ 77.342243] [c00000062b9a7b90] [c000000000503db8] .btrfs_kill_super+0x18/0xd0
[ 77.342411] [c00000062b9a7c10] [c0000000002958c8] .deactivate_locked_super+0x98/0xe0
[ 77.342573] [c00000062b9a7c90] [c0000000002be114] .cleanup_mnt+0x54/0xa0
[ 77.342723] [c00000062b9a7d10] [c0000000000d7e74] .task_work_run+0x124/0x180
[ 77.342862] [c00000062b9a7db0] [c00000000001c354] .do_notify_resume+0xa4/0xb0
[ 77.343030] [c00000062b9a7e30] [c00000000000c344] .ret_from_except_lite+0x70/0x74
[ 77.343187] Instruction dump:
[ 77.343276] 3b400000 e87d0c78 38810070 4bffab1d 60000000 2c230000 4182ff40 e8dfffc8
[ 77.343522] eb630008 7d5c3010 7d294910 7d2900d0 <0b090000> 7fbc3040 41dd0070 f95fffc8
[ 77.343771] ---[ end trace 8130fb71377d4ff8 ]---
[ 77.343857] BTRFS warning (device loop1): qgroup 5 reserved space underflow, have: 389120, to free: 393216
[ 77.735193] BTRFS info (device loop1): disabling disk space caching
[ 77.736629] BTRFS info (device loop1): has skinny extents
The above call trace happens because of the following:
|--------------------------------+-----------------------------------|
| Task A | Task B |
|--------------------------------+-----------------------------------|
| Write 4k bytes to a file | |
| at offset range [0, 4095] | |
| - __btrfs_buffered_write | |
| -- btrfs_check_data_free_space | |
| --- Set EXTENT_QGROUP_RESERVED | |
| bit for range [0, 64k-1] | |
| -- Copy 4k data from userspace | |
| to page cache | |
| | Write 4k bytes to the file |
| | at offset range [4096, 8191] |
| | - __btrfs_buffered_write |
| | -- btrfs_check_data_free_space |
| | --- Since EXTENT_QGROUP_RESERVED |
| | is already set we don't |
| | reserve qgroup space |
| | -- Assume the call to |
| | btrfs_delalloc_reserve_metadata() |
| | fails |
| | -- btrfs_free_reserved_data_space |
| | --- Clear EXTENT_QGROUP_RESERVED |
| | file range [4096, 8191] |
|--------------------------------+-----------------------------------|
On x86_64, It has been almost impossible to get the call to
btrfs_delalloc_reserve_metadata() in __btrfs_buffered_write() to fail. Hence I
have the following change in __btrfs_buffered_write() ...
if (pos != 2048)
ret = btrfs_delalloc_reserve_metadata(inode, reserve_bytes);
else
ret = 1;
if (ret) {
if (!only_release_metadata)
btrfs_free_reserved_data_space(inode, pos,
write_bytes);
else
btrfs_end_write_no_snapshoting(root);
break;
}
With the above change and by using max_inline=0 mount option, the following
command line will reproduce the call trace on an x86_64 machine,
$ xfs_io -f -c 'pwrite -b 2048 0 8192' -c sync /mnt/file-0.bin
--
chandan
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