crash unloading ntb_transport

crash unloading ntb_transport

[Allen Hubbe]

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Test attempted using jonmason/ntb at dfb7d24c5ad5c986f2417f52784738b67cfedd4d.
 
With latest, it crashes when removing the modules.
 
[ 1494.330594] ntb_hw_intel 0000:80:03.0: qp 0: Send Link Down
[ 1494.358126] ntb_hw_intel 0000:80:03.0: NTB Transport QP 0 freed
[ 1494.364771] ntb_hw_intel 0000:00:03.0: qp 0: Send Link Down
[ 1494.400171] ntb_hw_intel 0000:00:03.0: NTB Transport QP 0 freed
[ 1494.431502] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8
[ 1494.440267] IP: [<ffffffff816c3def>] down_write+0x1f/0x40
[ 1494.446312] PGD ff3231067 [ 1494.449136] PUD ff5600067
PMD 0 [ 1494.452760]
[ 1494.454430] Oops: 0002 [#1] SMP
 
Entering kdb (current=0xffff880ff4ea2c00, pid 1297) on processor 1 Oops: (null)
due to oops @ 0xffffffff816c3def
CPU: 1 PID: 1297 Comm: rmmod Not tainted 4.9.0-ntb #25
Hardware name: EMC 900-565-027/110-325-102B-00, BIOS 23.27 12/10/2014
task: ffff880ff4ea2c00 task.stack: ffffc9000d784000
RIP: 0010:[<ffffffff816c3def>]  [<ffffffff816c3def>] down_write+0x1f/0x40
RSP: 0018:ffffc9000d787d98  EFLAGS: 00010246
RAX: 00000000000000a8 RBX: 00000000000000a8 RCX: 0000000000000001
RDX: ffffffff00000001 RSI: ffff881ff5d49258 RDI: 00000000000000a8
RBP: ffffc9000d787da0 R08: ffffffffa01b2500 R09: 000000018022000f
R10: 00000000f7f6f701 R11: ffff880ff7f6f4b0 R12: ffff880ff3e53d98
R13: ffff880ff3e53de0 R14: ffff880ff3e53d40 R15: ffff880ff3e53d40
FS:  00007f65381b3740(0000) GS:ffff880fffc40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000a8 CR3: 0000000ff69e9000 CR4: 00000000001406e0
Stack:
ffff881ff5d49200 ffffc9000d787de0 ffffffff812ad0ed ffffffffa01390e0
ffff881ff5d49200 ffff881ff467cc00 0000000000000001 0000000000000000
ffff881ff4569800 ffffc9000d787e18 ffffffffa0135171 ffff881ff4569800
Call Trace:
[<ffffffff812ad0ed>] debugfs_remove_recursive+0x4d/0x190
[<ffffffffa0135171>] ntb_transport_free+0x61/0x160 [ntb_transport]
[<ffffffffa0031115>] ntb_remove+0x25/0x40 [ntb]
[<ffffffff8147e81a>] __device_release_driver+0x9a/0x140
[<ffffffff8147e9c8>] driver_detach+0xb8/0xc0
[<ffffffff8147d7f5>] bus_remove_driver+0x55/0xd0
[<ffffffff8147f18c>] driver_unregister+0x2c/0x50
[<ffffffffa003117e>] ntb_unregister_client+0xe/0x10 [ntb]
[<ffffffffa01379ae>] ntb_transport_exit+0x1c/0x66e [ntb_transport]
[<ffffffff8110d3ba>] SyS_delete_module+0x1ba/0x220
[<ffffffff81003a47>] do_syscall_64+0x67/0x180
[<ffffffff816c64ab>] entry_SYSCALL64_slow_path+0x25/0x25
Code: 66 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 53 48 89 fb e8 3e e1 ff ff 48 ba 01 00 00 00 ff ff ff ff 48 89 d8 <f0> 48 0f c1 10 85 d2 74 05 e8 53 2d c9 ff 65 48 8b 04 25 c0 d2

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