[DragonFlyBSD - Bug #2756] (New) Hit kernel panic while running hammer show cmd

[bugtracker-admin at leaf.dragonflybsd.org]

Issue #2756 has been reported by tkusumi.

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Bug #2756: Hit kernel panic while running hammer show cmd
http://bugs.dragonflybsd.org/issues/2756

* Author: tkusumi
* Status: New
* Priority: High
* Assignee: 
* Category: Kernel
* Target version: 4.0.x
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Hit kernel panic while running hammer show cmd. All I did was

# uname -r
4.0-RELEASE
# hammer -f /dev/serno/xxxxxxxx.s1d show > show.out

where /dev/serno/xxxxxxxx.s1d is a volume for / hammerfs with enough space left. It's running as a virtualbox guest on x86_64. It happens whenever the size of show.out gets around 250MB.

# df -h
Filesystem                           Size   Used  Avail Capacity  Mounted on
ROOT                                  74G   8.2G    66G    11%    /
...

x/i says it died at movl at dscheck+0x8b (ffffffff80618025)
ffffffff80618025:       44 8b 7b 0c             mov    0xc(%rbx),%r15d
ffffffff80618029:       44 3b 7d b8             cmp    -0x48(%rbp),%r15d
ffffffff8061802d:       77 28                   ja     ffffffff80618057 <dscheck+0xbd>

dscheck() was called as a sequence of btree lookup by hammer show. hammer_vop_strategy_read() -> hammer_ip_first() -> hammer_btree_lookup() -> btree_search() -> hammer_cursor_down() -> hammer_get_node() -> hammer_load_node() -> hammer_get_buffer() -> hammer_load_buffer() -> hammer_io_read() -> hammer_cluster_read() -> ... (failed to catch any further)

I saw disas of /boot/kernel/kernel and this movl seems to be null pointer dereference of *ssp at
if (slice >= ssp->dss_nslices)
of the following.

> struct bio *
> dscheck(cdev_t dev, struct bio *bio, struct diskslices *ssp)
> {
>         struct buf *bp = bio->bio_buf;
>         struct bio *nbio;
>         disklabel_t lp;
>         disklabel_ops_t ops;
>         long nsec;
>         u_int64_t secno;
>         u_int64_t endsecno;
>         u_int64_t slicerel_secno;
>         struct diskslice *sp;
>         u_int32_t part;
>         u_int32_t slice;
>         int shift;
>         int mask;
> 
>         slice = dkslice(dev);
>         part  = dkpart(dev);
> 
>         if (bio->bio_offset < 0) {
>                 kprintf("dscheck(%s): negative bio_offset %lld\n",
>                         devtoname(dev), (long long)bio->bio_offset);
>                 goto bad;
>         }
>         if (slice >= ssp->dss_nslices) {
>                 kprintf("dscheck(%s): slice too large %d/%d\n",
>                         devtoname(dev), slice, ssp->dss_nslices);
>                 goto bad;
>         }




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