scsi: zfcp: fix use-after-"free" in FC ingress path after TMF

When SCSI EH invokes zFCP's callbacks for eh_device_reset_handler() and
eh_target_reset_handler(), it expects us to relent the ownership over
the given scsi_cmnd and all other scsi_cmnds within the same scope - LUN
or target - when returning with SUCCESS from the callback ('release'
them).  SCSI EH can then reuse those commands.

We did not follow this rule to release commands upon SUCCESS; and if
later a reply arrived for one of those supposed to be released commands,
we would still make use of the scsi_cmnd in our ingress tasklet. This
will at least result in undefined behavior or a kernel panic because of
a wrong kernel pointer dereference.

To fix this, we NULLify all pointers to scsi_cmnds (struct zfcp_fsf_req
*)->data in the matching scope if a TMF was successful. This is done
under the locks (struct zfcp_adapter *)->abort_lock and (struct
zfcp_reqlist *)->lock to prevent the requests from being removed from
the request-hashtable, and the ingress tasklet from making use of the
scsi_cmnd-pointer in zfcp_fsf_fcp_cmnd_handler().

For cases where a reply arrives during SCSI EH, but before we get a
chance to NULLify the pointer - but before we return from the callback
-, we assume that the code is protected from races via the CAS operation
in blk_complete_request() that is called in scsi_done().

The following stacktrace shows an example for a crash resulting from the
previous behavior:

Unable to handle kernel pointer dereference at virtual kernel address fffffee17a672000
Oops: 0038 [#1] SMP
CPU: 2 PID: 0 Comm: swapper/2 Not tainted
task: 00000003f7ff5be0 ti: 00000003f3d38000 task.ti: 00000003f3d38000
Krnl PSW : 0404d00180000000 00000000001156b0 (smp_vcpu_scheduled+0x18/0x40)
           R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 EA:3
Krnl GPRS: 000000200000007e 0000000000000000 fffffee17a671fd8 0000000300000015
           ffffffff80000000 00000000005dfde8 07000003f7f80e00 000000004fa4e800
           000000036ce8d8f8 000000036ce8d9c0 00000003ece8fe00 ffffffff969c9e93
           00000003fffffffd 000000036ce8da10 00000000003bf134 00000003f3b07918
Krnl Code: 00000000001156a2: a7190000        lghi    %r1,0
           00000000001156a6: a7380015        lhi    %r3,21
          #00000000001156aa: e32050000008    ag    %r2,0(%r5)
          >00000000001156b0: 482022b0        lh    %r2,688(%r2)
           00000000001156b4: ae123000        sigp    %r1,%r2,0(%r3)
           00000000001156b8: b2220020        ipm    %r2
           00000000001156bc: 8820001c        srl    %r2,28
           00000000001156c0: c02700000001    xilf    %r2,1
Call Trace:
([<0000000000000000>] 0x0)
 [<000003ff807bdb8e>] zfcp_fsf_fcp_cmnd_handler+0x3de/0x490 [zfcp]
 [<000003ff807be30a>] zfcp_fsf_req_complete+0x252/0x800 [zfcp]
 [<000003ff807c0a48>] zfcp_fsf_reqid_check+0xe8/0x190 [zfcp]
 [<000003ff807c194e>] zfcp_qdio_int_resp+0x66/0x188 [zfcp]
 [<000003ff80440c64>] qdio_kick_handler+0xdc/0x310 [qdio]
 [<000003ff804463d0>] __tiqdio_inbound_processing+0xf8/0xcd8 [qdio]
 [<0000000000141fd4>] tasklet_action+0x9c/0x170
 [<0000000000141550>] __do_softirq+0xe8/0x258
 [<000000000010ce0a>] do_softirq+0xba/0xc0
 [<000000000014187c>] irq_exit+0xc4/0xe8
 [<000000000046b526>] do_IRQ+0x146/0x1d8
 [<00000000005d6a3c>] io_return+0x0/0x8
 [<00000000005d6422>] vtime_stop_cpu+0x4a/0xa0
([<0000000000000000>] 0x0)
 [<0000000000103d8a>] arch_cpu_idle+0xa2/0xb0
 [<0000000000197f94>] cpu_startup_entry+0x13c/0x1f8
 [<0000000000114782>] smp_start_secondary+0xda/0xe8
 [<00000000005d6efe>] restart_int_handler+0x56/0x6c
 [<0000000000000000>] 0x0
Last Breaking-Event-Address:
 [<00000000003bf12e>] arch_spin_lock_wait+0x56/0xb0

Suggested-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Fixes: ea127f9754 ("[PATCH] s390 (7/7): zfcp host adapter.") (tglx/history.git)
Cc: <stable@vger.kernel.org> #2.6.32+
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>