Re: XFS crashes on VMs

[Eric Sandeen <sandeen@sandeen.net>]

On 6/19/15 1:34 PM, Shrinand Javadekar wrote:
> I hit this problem again and captured the output of all the steps
> while repairing the filesystem. Here's the crash:
> http://pastie.org/private/prift1xjcc38s0jcvehvew

that starts with:

Jun 18 18:40:19 foods-12 kernel: [3639696.006884] ffff8801740f8000: 00 00 00 00 00 00 00 00 fb ee 00 00 00 00 00 00  ................
Jun 18 18:40:19 foods-12 kernel: [3639696.007056] ffff8801740f8010: 10 00 00 00 00 20 0f e0 00 00 00 00 00 00 00 00  ..... ..........
Jun 18 18:40:19 foods-12 kernel: [3639696.007140] ffff8801740f8020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
Jun 18 18:40:19 foods-12 kernel: [3639696.007230] ffff8801740f8030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................

I think there should have been other interesting bits prior to that line, can you check, and provide it please?  Full dmesg in a pastebin would be just fine.

xfs_attr3_leaf_write_verify at line 216 of file /build/buildd/linux-lts-trusty-3.13.0/fs/xfs/xfs_attr_leaf.c.  Caller 0xffffffffa00a193a

which is ... interesting; something went wrong on the way _to_ disk?

Ok, what is wrong, then.  here's the first 64 bytes of the buffer,
it contains:

typedef struct xfs_attr_leafblock {
        xfs_attr_leaf_hdr_t     hdr;    /* constant-structure header block */

where

typedef struct xfs_attr_leaf_hdr {      /* constant-structure header block */
        xfs_da_blkinfo_t info;          /* block type, links, etc. */
        __be16  count;                  /* count of active leaf_entry's */
        __be16  usedbytes;              /* num bytes of names/values stored */
        __be16  firstused;              /* first used byte in name area */
        __u8    holes;                  /* != 0 if blk needs compaction */
        __u8    pad1;
        xfs_attr_leaf_map_t freemap[XFS_ATTR_LEAF_MAPSIZE];
                                        /* N largest free regions */
} xfs_attr_leaf_hdr_t;

and

typedef struct xfs_da_blkinfo {
        __be32          forw;                   /* previous block in list */
        __be32          back;                   /* following block in list */
        __be16          magic;                  /* validity check on block */
        __be16          pad;                    /* unused */
} xfs_da_blkinfo_t;

so:

00 00 00 00 00 00 00 00 fb ee 00 00 00 00 00 00
|   forw   |    back   |magic| pad |count|used|
10 00 00 00 00 20 0f e0 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

and the only thing the verifier checks on non-crc is
magic (which is good), and count (which is what tripped here)

        if (xfs_sb_version_hascrc(&mp->m_sb)) {
		<snip>
        } else {
                if (ichdr.magic != XFS_ATTR_LEAF_MAGIC)
                        return false;
        }
        if (ichdr.count == 0)
                return false;

so this failed to verify because count was 0.

> And the output of the xfs_repair steps (also attached if needed):
> http://pastie.org/private/gvq3aiisudfhy69ezagw

Ok, no on-disk corruption, that's good.

Can you please provide as much info as possible about your system
and setup?

http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F

-Eric

> Hope this can provide some insights.
> 
> -Shri

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