nvme-fabrics: crash at nvme connect-all

[Steve Wise]

> > I applied your patch and it does avoid the crash.  So the connect to the target
> > device via cxgb4 that I setup to fail in ib_alloc_mr(), correctly fails w/o
> > crashing.   After this connect failure, I tried to connect the same target
> > device but via another rdma path (mlx4 instead of cxgb4 which was setup to fail)
> > and got a different failure.  Not sure if this is a regression from your fix or
> > just another error path problem:
> >
> > BUG: unable to handle kernel paging request at ffff881027d00e00
> > IP: [<ffffffffa04c5a49>] nvmf_parse_options+0x369/0x4a0 [nvme_fabrics]
> 
> Could you find out which line of code this is?

>From objdump -S -l nvme-fabrics.ok, nvmf_parse_options starts at 6e0:

---
00000000000006e0 <nvmf_parse_options>:
nvmf_parse_options():
/usr/local/src/linux-2.6/drivers/nvme/host/fabrics.c:515
        { NVMF_OPT_ERR,                 NULL                    }
};

static int nvmf_parse_options(struct nvmf_ctrl_options *opts,
                const char *buf)
{
     6e0:       55                      push   %rbp
----

So 0x6e0+0x369 = 0xa49 which is in an inline atomic_add_return(), I think:

---
atomic_add_return():
/usr/local/src/linux-2.6/./arch/x86/include/asm/atomic.h:156
 *
 * Atomically adds @i to @v and returns @i + @v
 */
static __always_inline int atomic_add_return(int i, atomic_t *v)
{
        return i + xadd(&v->counter, i);
     a3d:       48 8b 15 00 00 00 00    mov    0x0(%rip),%rdx        # a44 <nvmf_parse_options+0x364>
     a44:       b8 01 00 00 00          mov    $0x1,%eax
     a49:       f0 0f c1 02             lock xadd %eax,(%rdx)
     a4d:       83 c0 01                add    $0x1,%eax
kref_get():
/usr/local/src/linux-2.6/include/linux/kref.h:46
{
        /* If refcount was 0 before incrementing then we have a race
         * condition when this kref is freeing by some other thread right now.
         * In this case one should use kref_get_unless_zero()
         */
        WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
     a50:       83 f8 01                cmp    $0x1,%eax
     a53:       7e 1e                   jle    a73 <nvmf_parse_options+0x393>
nvmf_parse_options():
/usr/local/src/linux-2.6/drivers/nvme/host/fabrics.c:689
---