If the number of packets in a user sdma request does not match
the actual iovectors being sent, sdma_cleanup can be called on
an uninitialized request structure, resulting in a crash similar
to this:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffffc0ae8bb7>] __sdma_txclean+0x57/0x1e0 [hfi1]
PGD 8000001044f61067 PUD 1052706067 PMD 0
Oops: 0000 [#1] SMP
CPU: 30 PID: 69912 Comm: upsm Kdump: loaded Tainted: G           OE
------------   3.10.0-862.el7.x86_64 #1
Hardware name: Intel Corporation S2600KPR/S2600KPR, BIOS
SE5C610.86B.01.01.0019.101220160604 10/12/2016
task: ffff8b331c890000 ti: ffff8b2ed1f98000 task.ti: ffff8b2ed1f98000
RIP: 0010:[<ffffffffc0ae8bb7>]  [<ffffffffc0ae8bb7>] __sdma_txclean+0x57/0x1e0
[hfi1]
RSP: 0018:ffff8b2ed1f9bab0  EFLAGS: 00010286
RAX: 0000000000008b2b RBX: ffff8b2adf6e0000 RCX: 0000000000000000
RDX: 00000000000000a0 RSI: ffff8b2e9eedc540 RDI: ffff8b2adf6e0000
RBP: ffff8b2ed1f9bad8 R08: 0000000000000000 R09: ffffffffc0b04a06
R10: ffff8b331c890190 R11: ffffe6ed00bf1840 R12: ffff8b3315480000
R13: ffff8b33154800f0 R14: 00000000fffffff2 R15: ffff8b2e9eedc540
FS:  00007f035ac47740(0000) GS:ffff8b331e100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 0000000c03fe6000 CR4: 00000000001607e0
Call Trace:
 [<ffffffffc0b0570d>] user_sdma_send_pkts+0xdcd/0x1990 [hfi1]
 [<ffffffff9fe75fb0>] ? gup_pud_range+0x140/0x290
 [<ffffffffc0ad3105>] ? hfi1_mmu_rb_insert+0x155/0x1b0 [hfi1]
 [<ffffffffc0b0777b>] hfi1_user_sdma_process_request+0xc5b/0x11b0 [hfi1]
 [<ffffffffc0ac193a>] hfi1_aio_write+0xba/0x110 [hfi1]
 [<ffffffffa001a2bb>] do_sync_readv_writev+0x7b/0xd0
 [<ffffffffa001bede>] do_readv_writev+0xce/0x260
 [<ffffffffa022b089>] ? tty_ldisc_deref+0x19/0x20
 [<ffffffffa02268c0>] ? n_tty_ioctl+0xe0/0xe0
 [<ffffffffa001c105>] vfs_writev+0x35/0x60
 [<ffffffffa001c2bf>] SyS_writev+0x7f/0x110
 [<ffffffffa051f7d5>] system_call_fastpath+0x1c/0x21
Code: 06 49 c7 47 18 00 00 00 00 0f 87 89 01 00 00 5b 41 5c 41 5d 41 5e 41 5f
5d c3 66 2e 0f 1f 84 00 00 00 00 00 48 8b 4e 10 48 89 fb <48> 8b 51 08 49 89 d4
83 e2 0c 41 81 e4 00 e0 00 00 48 c1 ea 02
RIP  [<ffffffffc0ae8bb7>] __sdma_txclean+0x57/0x1e0 [hfi1]
 RSP <ffff8b2ed1f9bab0>
CR2: 0000000000000008

There are two exit points from user_sdma_send_pkts().  One (free_tx)
merely frees the slab entry and one (free_txreq) cleans the sdma_txreq
prior to freeing the slab entry.   The free_txreq variation can only be
called after one of the sdma_init*() variations has been called.

In the panic case, the slab entry had been allocated but not inited.

Fix the issue by exiting through free_tx thus avoiding sdma_clean().

Cc: <stable@vger.kernel.org> # 4.9.x+
Fixes: 77241056 ("IB/hfi1: add driver files")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Lukasz Odzioba <lukasz.odzioba@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>