[PATCH] xfs: do not unconditionally enable hasalign feature on V5 filesystems

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

On a ppc64 system, executing generic/256 test with 32k block size gives
the following call trace,

XFS: Assertion failed: args->maxlen > 0, file: /root/repos/linux/fs/xfs/libxfs/xfs_alloc.c, line: 2026

kernel BUG at /root/repos/linux/fs/xfs/xfs_message.c:113!
Oops: Exception in kernel mode, sig: 5 [#1]
SMP NR_CPUS=2048
DEBUG_PAGEALLOC
NUMA
pSeries
Modules linked in:
CPU: 2 PID: 19361 Comm: mkdir Not tainted 4.10.0-rc5 #58
task: c000000102606d80 task.stack: c0000001026b8000
NIP: c0000000004ef798 LR: c0000000004ef798 CTR: c00000000082b290
REGS: c0000001026bb090 TRAP: 0700   Not tainted  (4.10.0-rc5)
MSR: 8000000000029032 <SF,EE,ME,IR,DR,RI>
CR: 28004428  XER: 00000000
CFAR: c0000000004ef180 SOFTE: 1
GPR00: c0000000004ef798 c0000001026bb310 c000000001157300 ffffffffffffffea
GPR04: 000000000000000a c0000001026bb130 0000000000000000 ffffffffffffffc0
GPR08: 00000000000000d1 0000000000000021 00000000ffffffd1 c000000000dd4990
GPR12: 0000000022004444 c00000000fe00800 0000000020000000 0000000000000000
GPR16: 0000000000000000 0000000043a606fc 0000000043a76c08 0000000043a1b3d0
GPR20: 000001002a35cd60 c0000001026bbb80 0000000000000000 0000000000000001
GPR24: 0000000000000240 0000000000000004 c00000062dc55000 0000000000000000
GPR28: 0000000000000004 c00000062ecd9200 0000000000000000 c0000001026bb6c0
NIP [c0000000004ef798] .assfail+0x28/0x30
LR [c0000000004ef798] .assfail+0x28/0x30
Call Trace:
[c0000001026bb310] [c0000000004ef798] .assfail+0x28/0x30 (unreliable)
[c0000001026bb380] [c000000000455d74] .xfs_alloc_space_available+0x194/0x1b0
[c0000001026bb410] [c00000000045b914] .xfs_alloc_fix_freelist+0x144/0x480
[c0000001026bb580] [c00000000045c368] .xfs_alloc_vextent+0x698/0xa90
[c0000001026bb650] [c0000000004a6200] .xfs_ialloc_ag_alloc+0x170/0x820
[c0000001026bb7c0] [c0000000004a9098] .xfs_dialloc+0x158/0x320
[c0000001026bb8a0] [c0000000004e628c] .xfs_ialloc+0x7c/0x610
[c0000001026bb990] [c0000000004e8138] .xfs_dir_ialloc+0xa8/0x2f0
[c0000001026bbaa0] [c0000000004e8814] .xfs_create+0x494/0x790
[c0000001026bbbf0] [c0000000004e5ebc] .xfs_generic_create+0x2bc/0x410
[c0000001026bbce0] [c0000000002b4a34] .vfs_mkdir+0x154/0x230
[c0000001026bbd70] [c0000000002bc444] .SyS_mkdirat+0x94/0x120
[c0000001026bbe30] [c00000000000b760] system_call+0x38/0xfc
Instruction dump:
4e800020 60000000 7c0802a6 7c862378 3c82ffca 7ca72b78 38841c18 7c651b78
38600000 f8010010 f821ff91 4bfff94d <0fe00000> 60000000 7c0802a6 7c892378

The root cause of the problem is due to the fact that
xfs_sb_version_hasalign() returns true when we are working on a V5
filesystem. Due to this args.minalignslop (in xfs_ialloc_ag_alloc())
gets the unsigned equivalent of -1 assigned to it. This later causes
alloc_len in xfs_alloc_space_available() to have a value of 0. In such a
scenario when args.total is also 0, the assert statement
"ASSERT(args->maxlen > 0);" fails.

This commit fixes the bug by checking for the existance of
XFS_SB_VERSION_ALIGNBIT bit in xfs_sb->sb_versionnum field even on V5
filesystems.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
PS: From what I could understand from other code paths,
xfs_alloc_arg->total must be set to the sum of space required by the
current code path and the space already reserved in the current
transaction. Please let me know if my understanding is
incorrect. Also, In the code path listed in the above call trace we
have xfs_alloc_arg->total set to 0 which probably isn't correct
either.

 fs/xfs/libxfs/xfs_format.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 6b7579e..57a5264 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -346,8 +346,7 @@ static inline void xfs_sb_version_addquota(struct xfs_sb *sbp)
 
 static inline bool xfs_sb_version_hasalign(struct xfs_sb *sbp)
 {
-	return (XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5 ||
-		(sbp->sb_versionnum & XFS_SB_VERSION_ALIGNBIT));
+	return (sbp->sb_versionnum & XFS_SB_VERSION_ALIGNBIT);
 }
 
 static inline bool xfs_sb_version_hasdalign(struct xfs_sb *sbp)
-- 
2.5.5