The index r_tid_ack is used to indicate the next TID RDMA WRITE request to
acknowledge in the ring s_ack_queue[] on the responder side and should be
set to a valid index other than its initial value before r_tid_tail is
advanced to the next TID RDMA WRITE request and particularly before a TID
RDMA ACK is built. Otherwise, a NULL pointer dereference may result:

  BUG: unable to handle kernel paging request at ffff9a32d27abff8
  IP: [<ffffffffc0d87ea6>] hfi1_make_tid_rdma_pkt+0x476/0xcb0 [hfi1]
  PGD 2749032067 PUD 0
  Oops: 0000 1 SMP
  Modules linked in: osp(OE) ofd(OE) lfsck(OE) ost(OE) mgc(OE) osd_zfs(OE) lquota(OE) lustre(OE) lmv(OE) mdc(OE) lov(OE) fid(OE) fld(OE) ko2iblnd(OE) ptlrpc(OE) obdclass(OE) lnet(OE) libcfs(OE) ib_ipoib(OE) hfi1(OE) rdmavt(OE) nfsv3 nfs_acl rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache ib_isert iscsi_target_mod target_core_mod ib_ucm dm_mirror dm_region_hash dm_log mlx5_ib dm_mod zfs(POE) rpcrdma sunrpc rdma_ucm ib_uverbs opa_vnic ib_iser zunicode(POE) ib_umad zavl(POE) icp(POE) sb_edac intel_powerclamp coretemp rdma_cm intel_rapl iosf_mbi iw_cm libiscsi scsi_transport_iscsi kvm ib_cm iTCO_wdt mxm_wmi iTCO_vendor_support irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd zcommon(POE) znvpair(POE) pcspkr spl(OE) mei_me
  sg mei ioatdma lpc_ich joydev i2c_i801 shpchp ipmi_si ipmi_devintf ipmi_msghandler wmi acpi_power_meter ip_tables xfs libcrc32c sd_mod crc_t10dif crct10dif_generic mgag200 mlx5_core drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ixgbe ahci ttm mlxfw ib_core libahci devlink mdio crct10dif_pclmul crct10dif_common drm ptp libata megaraid_sas crc32c_intel i2c_algo_bit pps_core i2c_core dca [last unloaded: rdmavt]
  CPU: 15 PID: 68691 Comm: kworker/15:2H Kdump: loaded Tainted: P W OE ------------ 3.10.0-862.2.3.el7_lustre.x86_64 #1
  Hardware name: Intel Corporation S2600WTT/S2600WTT, BIOS SE5C610.86B.01.01.0016.033120161139 03/31/2016
  Workqueue: hfi0_0 _hfi1_do_tid_send [hfi1]
  task: ffff9a01f47faf70 ti: ffff9a11776a8000 task.ti: ffff9a11776a8000
  RIP: 0010:[<ffffffffc0d87ea6>] [<ffffffffc0d87ea6>] hfi1_make_tid_rdma_pkt+0x476/0xcb0 [hfi1]
  RSP: 0018:ffff9a11776abd08 EFLAGS: 00010002
  RAX: ffff9a32d27abfc0 RBX: ffff99f2d27aa000 RCX: 00000000ffffffff
  RDX: 0000000000000000 RSI: 0000000000000220 RDI: ffff99f2ffc05300
  RBP: ffff9a11776abd88 R08: 000000000001c310 R09: ffffffffc0d87ad4
  R10: 0000000000000000 R11: 0000000000000000 R12: ffff9a117a423c00
  R13: ffff9a117a423c00 R14: ffff9a03500c0000 R15: ffff9a117a423cb8
  FS: 0000000000000000(0000) GS:ffff9a117e9c0000(0000) knlGS:0000000000000000
  CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: ffff9a32d27abff8 CR3: 0000002748a0e000 CR4: 00000000001607e0
  Call Trace:
  [<ffffffffc0d88874>] _hfi1_do_tid_send+0x194/0x320 [hfi1]
  [<ffffffffaf0b2dff>] process_one_work+0x17f/0x440
  [<ffffffffaf0b3ac6>] worker_thread+0x126/0x3c0
  [<ffffffffaf0b39a0>] ? manage_workers.isra.24+0x2a0/0x2a0
  [<ffffffffaf0bae31>] kthread+0xd1/0xe0
  [<ffffffffaf0bad60>] ? insert_kthread_work+0x40/0x40
  [<ffffffffaf71f5f7>] ret_from_fork_nospec_begin+0x21/0x21
  [<ffffffffaf0bad60>] ? insert_kthread_work+0x40/0x40
  hfi1 0000:05:00.0: hfi1_0: reserved_op: opcode 0xf2, slot 2, rsv_used 1, rsv_ops 1
  Code: 00 00 41 8b 8d d8 02 00 00 89 c8 48 89 45 b0 48 c1 65 b0 06 48 8b 83 a0 01 00 00 48 01 45 b0 48 8b 45 b0 41 80 bd 10 03 00 00 00 <48> 8b 50 38 4c 8d 7a 50 74 45 8b b2 d0 00 00 00 85 f6 0f 85 72
  RIP [<ffffffffc0d87ea6>] hfi1_make_tid_rdma_pkt+0x476/0xcb0 [hfi1]
  RSP <ffff9a11776abd08>
  CR2: ffff9a32d27abff8

This problem can happen if a RESYNC request is received before r_tid_ack
is modified.

This patch fixes the issue by making sure that r_tid_ack is set to a valid
value before a TID RDMA ACK is built. Functions are defined to simplify
the code.

Fixes: 07b92370 ("IB/hfi1: Add functions to receive TID RDMA WRITE request")
Fixes: 7cf0ad67 ("IB/hfi1: Add a function to receive TID RDMA RESYNC packet")
Link: https://lore.kernel.org/r/20191025195830.106825.44022.stgit@awfm-01.aw.intel.com
Cc: <stable@vger.kernel.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>