With IRQF_SHARED flag set and CONFIG_DEBUG_SHIRQ enabled
module removal may result in panic in sdma_interrupt() routine
if associated sdma context was released before pci_free_irq();

[ 9198.939885] BUG: unable to handle kernel NULL pointer dereference at           (null)
[ 9198.940514] IP: sdma_make_progress+0xa5/0x450 [hfi1]
[ 9198.941114] PGD 170bdc0067 P4D 170bdc0067 PUD 172063e067 PMD 0
[ 9198.941783] Oops: 0000 [#1] SMP
.....
[ 9198.958877] CPU: 132 PID: 64173 Comm: rmmod Tainted: G           OE   4.14.0-rc4+ #1
[ 9198.961032] Hardware name: Intel Corporation S7200AP/S7200AP, BIOS S72C610.86B.01.02.0118.080620171935 08/06/2017
[ 9198.963323] task: ffff9681397f0000 task.stack: ffffae1647c40000
[ 9198.965695] RIP: 0010:sdma_make_progress+0xa5/0x450 [hfi1]
[ 9198.968082] RSP: 0018:ffffae1647c43be8 EFLAGS: 00010046
[ 9198.970503] RAX: 0000000000000000 RBX: ffff9680ce8b5ca8 RCX: 0000000000000000
[ 9198.973006] RDX: 0000000000000000 RSI: 0000000001a00d28 RDI: ffff9680ce8b5ca0
[ 9198.975546] RBP: ffffae1647c43c40 R08: ffff96814325ec00 R09: 00000000ffffffff
[ 9198.978142] R10: 000000004325e501 R11: ffff96814325ec00 R12: ffff9680ce8b5c44
[ 9198.980779] R13: ffff9680ce8b5ca0 R14: 0000000000000000 R15: ffff9680ce8b5b00
[ 9198.983462] FS:  00007f31196ba740(0000) GS:ffff96819df00000(0000) knlGS:0000000000000000
[ 9198.986231] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9198.989036] CR2: 0000000000000000 CR3: 000000170833f000 CR4: 00000000001406e0
[ 9198.991911] Call Trace:
[ 9198.994847]  sdma_engine_interrupt+0x82/0x100 [hfi1]
[ 9198.997852]  sdma_interrupt+0x61/0xc0 [hfi1]
[ 9199.000852]  __free_irq+0x1b3/0x2d0
[ 9199.003873]  free_irq+0x35/0x70
[ 9199.006909]  pci_free_irq+0x1c/0x30
[ 9199.009999]  clean_up_interrupts+0x53/0xf0 [hfi1]
[ 9199.013137]  hfi1_start_cleanup+0x117/0x190 [hfi1]
[ 9199.016315]  postinit_cleanup+0x1d/0x270 [hfi1]
[ 9199.019529]  remove_one+0x1f3/0x210 [hfi1]
[ 9199.022738]  pci_device_remove+0x39/0xc0
[ 9199.025974]  device_release_driver_internal+0x141/0x210
[ 9199.029268]  driver_detach+0x3f/0x80
[ 9199.032580]  bus_remove_driver+0x55/0xd0
[ 9199.035931]  driver_unregister+0x2c/0x50
[ 9199.039321]  pci_unregister_driver+0x2a/0xa0
[ 9199.042755]  hfi1_mod_cleanup+0x10/0xb50 [hfi1]
[ 9199.046196]  SyS_delete_module+0x171/0x250
...

Fix by exporting sdma_clean() and removing from sdma_exit().
sdma_exit() now just manipulates the engine state,
leaving the memory free to sdma_clean() which is now called
just before the dd is freed.
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Michael J Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Alex Estrin <alex.estrin@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>