target crash / host hang with nvme-all.3 branch of nvme-fabrics

[Steve Wise]

> hrm...
> 
> Forcing more reconnects, I just hit this.  It looks different from the other
> issue:
> 
> general protection fault: 0000 [#1] SMP
> Modules linked in: rdma_ucm iw_cxgb4 cxgb4 nvmet_rdma rdma_cm iw_cm
> nvmet
> null_blk configfs ip6table_filter ip6_tables ebtable_nat ebtables
> nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ipt_REJECT nf_reject_
> ipv4 xt_CHECKSUM iptable_mangle iptable_filter ip_tables bridge autofs4 8021q
> garp stp llc ipmi_devintf cachefiles fscache ib_ipoib ib_cm ib_uverbs ib_umad
> iw_nes libcrc32c iw_cxgb3 cxgb3 mdio ib_qib rdmavt mlx4_en i   b_mthca
> dm_mirror
> dm_region_hash dm_log vhost_net macvtap macvlan vhost tun kvm_intel kvm
> irqbypass uinput iTCO_wdt iTCO_vendor_support mxm_wmi pcspkr mlx4_ib
> ib_core
> ipv6 mlx4_core dm_mod i2c_i801 sg lpc_ich mfd_cor   e nvme nvme_core
> acpi_cpufreq ioatdma igb dca i2c_algo_bit i2c_core ptp pps_core wmi ext4(E)
> mbcache(E) jbd2(E) sd_mod(E) ahci(E) libahci(E) [last unloaded: cxgb4]
> CPU: 3 PID: 19213 Comm: kworker/3:10 Tainted: G            E
> 4.7.0-rc2-nvmf-all.3+rxe+ #84
> Hardware name: Supermicro X9DR3-F/X9DR3-F, BIOS 3.2a 07/09/2015
> Workqueue: events nvmet_rdma_release_queue_work [nvmet_rdma]
> task: ffff88103d68cf00 ti: ffff880fdf7a4000 task.ti: ffff880fdf7a4000
> RIP: 0010:[<ffffffffa01ef5b7>]  [<ffffffffa01ef5b7>]
> nvmet_rdma_free_rsps+0x67/0xb0 [nvmet_rdma]
> RSP: 0018:ffff880fdf7a7bb8  EFLAGS: 00010202
> RAX: dead000000000100 RBX: 000000000000001f RCX: 0000000000000001
> RDX: dead000000000200 RSI: ffff880fdd884290 RDI: dead000000000200
> RBP: ffff880fdf7a7bf8 R08: dead000000000100 R09: ffff88103c768140
> R10: ffff88103c7682c0 R11: ffff88103c768340 R12: 00000000000044c8
> R13: ffff88103db39c00 R14: 0000000000000100 R15: ffff88103e29cec0
> FS:  0000000000000000(0000) GS:ffff88107f2c0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000001016b00 CR3: 000000103bcb7000 CR4: 00000000000406e0
> Stack:
>  ffff880fdd8a23f8 00000000ffac1a05 ffff880fdf7a7bf8 ffff88103db39c00
>  ffff88103c64cc00 ffffe8ffffac1a00 0000000000000000 ffffe8ffffac1a05
>  ffff880fdf7a7c18 ffffffffa01ef652 0000000000000246 ffff88103e29cec0
> Call Trace:
>  [<ffffffffa01ef652>] nvmet_rdma_free_queue+0x52/0xa0 [nvmet_rdma]
>  [<ffffffffa01ef6d3>] nvmet_rdma_release_queue_work+0x33/0x70 [nvmet_rdma]
>  [<ffffffff8107cb5b>] process_one_work+0x17b/0x510
>  [<ffffffff8161495c>] ? __schedule+0x23c/0x630
>  [<ffffffff810c6c4c>] ? del_timer_sync+0x4c/0x60
>  [<ffffffff8107da0b>] ? maybe_create_worker+0x8b/0x110
>  [<ffffffff81614eb0>] ? schedule+0x40/0xb0
>  [<ffffffff8107dbf6>] worker_thread+0x166/0x580
>  [<ffffffff8161495c>] ? __schedule+0x23c/0x630
>  [<ffffffff8108e162>] ? default_wake_function+0x12/0x20
>  [<ffffffff8109fc26>] ? __wake_up_common+0x56/0x90
>  [<ffffffff8107da90>] ? maybe_create_worker+0x110/0x110
>  [<ffffffff81614eb0>] ? schedule+0x40/0xb0
>  [<ffffffff8107da90>] ? maybe_create_worker+0x110/0x110
>  [<ffffffff8108255c>] kthread+0xcc/0xf0
>  [<ffffffff8108cade>] ? schedule_tail+0x1e/0xc0
>  [<ffffffff816186cf>] ret_from_fork+0x1f/0x40
>  [<ffffffff81082490>] ? kthread_freezable_should_stop+0x70/0x70
> Code: b8 00 01 00 00 00 00 ad de 48 bf 00 02 00 00 00 00 ad de 83 c3 01 49 81
c4
> 38 02 00 00 48 8b 86 28 02 00 00 48 8b 96 30 02 00 00 <48> 89 50 08 48 89 45
c0
> 48 89 02 48 89 be 30 02 00 00 4c 89 ff
> RIP  [<ffffffffa01ef5b7>] nvmet_rdma_free_rsps+0x67/0xb0 [nvmet_rdma]
>  RSP <ffff880fdf7a7bb8>
> ---[ end trace a30265f72371b5ce ]---
> 


It crashed in list_del().  I assume rsp was garbage since it was a GPF.

----
static void nvmet_rdma_free_rsps(struct nvmet_rdma_queue *queue)
{
        struct nvmet_rdma_device *ndev = queue->dev;
        int i, nr_rsps = queue->recv_queue_size * 2;

        for (i = 0; i < nr_rsps; i++) {
                struct nvmet_rdma_rsp *rsp = &queue->rsps[i];

                list_del(&rsp->free_list); <----- HERE
                nvmet_rdma_free_rsp(ndev, rsp);
        }
        kfree(queue->rsps);
}
---

Here is the assembler:

static inline void __list_del(struct list_head * prev, struct list_head * next)
{
        next->prev = prev;
    15b7:       48 89 50 08             mov    %rdx,0x8(%rax)

And RAX/RDX are list poison values, I think:

RAX: dead000000000100
RDX: dead000000000200

So rsp was already deleted off its list?  Or has rsp been freed?