scsi: lpfc: fix oops/BUG in lpfc_sli_ringtxcmpl_put()

The BUG_ON() recently introduced in lpfc_sli_ringtxcmpl_put() is hit in
the lpfc_els_abort() > lpfc_sli_issue_abort_iotag() >
lpfc_sli_abort_iotag_issue() function path [similar names], due to
'piocb->vport == NULL':

	BUG_ON(!piocb || !piocb->vport);

This happens because lpfc_sli_abort_iotag_issue() doesn't set the
'abtsiocbp->vport' pointer -- but this is not the problem.

Previously, lpfc_sli_ringtxcmpl_put() accessed 'piocb->vport' only if
'piocb->iocb.ulpCommand' is neither CMD_ABORT_XRI_CN nor
CMD_CLOSE_XRI_CN, which are the only possible values for
lpfc_sli_abort_iotag_issue():

    lpfc_sli_ringtxcmpl_put():

        if ((unlikely(pring->ringno == LPFC_ELS_RING)) &&
           (piocb->iocb.ulpCommand != CMD_ABORT_XRI_CN) &&
           (piocb->iocb.ulpCommand != CMD_CLOSE_XRI_CN) &&
            (!(piocb->vport->load_flag & FC_UNLOADING)))

    lpfc_sli_abort_iotag_issue():

        if (phba->link_state >= LPFC_LINK_UP)
                iabt->ulpCommand = CMD_ABORT_XRI_CN;
        else
                iabt->ulpCommand = CMD_CLOSE_XRI_CN;

So, this function path would not have hit this possible NULL pointer
dereference before.

In order to fix this regression, move the second part of the BUG_ON()
check prior to the pointer dereference that it does check for.

For reference, this is the stack trace observed. The problem happened
because an unsolicited event was received - a PLOGI was received after
our PLOGI was issued but not yet complete, so the discovery state
machine goes on to sw-abort our PLOGI.

    kernel BUG at drivers/scsi/lpfc/lpfc_sli.c:1326!
    Oops: Exception in kernel mode, sig: 5 [#1]
    <...>
    NIP [...] lpfc_sli_ringtxcmpl_put+0x1c/0xf0 [lpfc]
    LR  [...] __lpfc_sli_issue_iocb_s4+0x188/0x200 [lpfc]
    Call Trace:
    [...] [...] __lpfc_sli_issue_iocb_s4+0xb0/0x200 [lpfc] (unreliable)
    [...] [...] lpfc_sli_issue_abort_iotag+0x2b4/0x350 [lpfc]
    [...] [...] lpfc_els_abort+0x1a8/0x4a0 [lpfc]
    [...] [...] lpfc_rcv_plogi+0x6d4/0x700 [lpfc]
    [...] [...] lpfc_rcv_plogi_plogi_issue+0xd8/0x1d0 [lpfc]
    [...] [...] lpfc_disc_state_machine+0xc0/0x2b0 [lpfc]
    [...] [...] lpfc_els_unsol_buffer+0xcc0/0x26c0 [lpfc]
    [...] [...] lpfc_els_unsol_event+0xa8/0x220 [lpfc]
    [...] [...] lpfc_complete_unsol_iocb+0xb8/0x138 [lpfc]
    [...] [...] lpfc_sli4_handle_received_buffer+0x6a0/0xec0 [lpfc]
    [...] [...] lpfc_sli_handle_slow_ring_event_s4+0x1c4/0x240 [lpfc]
    [...] [...] lpfc_sli_handle_slow_ring_event+0x24/0x40 [lpfc]
    [...] [...] lpfc_do_work+0xd88/0x1970 [lpfc]
    [...] [...] kthread+0x108/0x130
    [...] [...] ret_from_kernel_thread+0x5c/0xbc
    <...>

Cc: stable@vger.kernel.org # v4.8
Fixes: 22466da ("lpfc: Fix possible NULL pointer dereference")
Reported-by: Harsha Thyagaraja <hathyaga@in.ibm.com>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Mauricio Faria de Oliveira

drivers/scsi/lpfc/lpfc_sli.c

@@ -1323,18 +1323,20 @@ lpfc_sli_ringtxcmpl_put(struct lpfc_hba *phba, struct lpfc_sli_ring *pring,
 {
 	lockdep_assert_held(&phba->hbalock);
 
-	BUG_ON(!piocb || !piocb->vport);
+	BUG_ON(!piocb);
 
 	list_add_tail(&piocb->list, &pring->txcmplq);
 	piocb->iocb_flag |= LPFC_IO_ON_TXCMPLQ;
 
 	if ((unlikely(pring->ringno == LPFC_ELS_RING)) &&
 	   (piocb->iocb.ulpCommand != CMD_ABORT_XRI_CN) &&
-	   (piocb->iocb.ulpCommand != CMD_CLOSE_XRI_CN) &&
-	    (!(piocb->vport->load_flag & FC_UNLOADING)))
-		mod_timer(&piocb->vport->els_tmofunc,
-			  jiffies +
-			  msecs_to_jiffies(1000 * (phba->fc_ratov << 1)));
+	   (piocb->iocb.ulpCommand != CMD_CLOSE_XRI_CN)) {
+		BUG_ON(!piocb->vport);
+		if (!(piocb->vport->load_flag & FC_UNLOADING))
+			mod_timer(&piocb->vport->els_tmofunc,
+				  jiffies +
+				  msecs_to_jiffies(1000 * (phba->fc_ratov << 1)));
+	}
 
 	return 0;
 }