scsi: qla2xxx: Fix null pointer access during disconnect from subsystem

scsi: qla2xxx: Fix null pointer access during disconnect from subsystem

[ Upstream commit 83949613fac61e8e37eadf8275bf072342302f4e ]

NVMEAsync command is being submitted to QLA while the same NVMe controller
is in the middle of reset. The reset path has deleted the association and
freed aen_op->fcp_req.private. Add a check for this private pointer before
issuing the command.

...
 6 [ffffb656ca11fce0] page_fault at ffffffff8c00114e
    [exception RIP: qla_nvme_post_cmd+394]
    RIP: ffffffffc0d012ba  RSP: ffffb656ca11fd98  RFLAGS: 00010206
    RAX: ffff8fb039eda228  RBX: ffff8fb039eda200  RCX: 00000000000da161
    RDX: ffffffffc0d4d0f0  RSI: ffffffffc0d26c9b  RDI: ffff8fb039eda220
    RBP: 0000000000000013   R8: ffff8fb47ff6aa80   R9: 0000000000000002
    R10: 0000000000000000  R11: ffffb656ca11fdc8  R12: ffff8fb27d04a3b0
    R13: ffff8fc46dd98a58  R14: 0000000000000000  R15: ffff8fc4540f0000
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 7 [ffffb656ca11fe08] nvme_fc_start_fcp_op at ffffffffc0241568 [nvme_fc]
 8 [ffffb656ca11fe50] nvme_fc_submit_async_event at ffffffffc0241901 [nvme_fc]
 9 [ffffb656ca11fe68] nvme_async_event_work at ffffffffc014543d [nvme_core]
10 [ffffb656ca11fe98] process_one_work at ffffffff8b6cd437
11 [ffffb656ca11fed8] worker_thread at ffffffff8b6cdcef
12 [ffffb656ca11ff10] kthread at ffffffff8b6d3402
13 [ffffb656ca11ff50] ret_from_fork at ffffffff8c000255

--
PID: 37824  TASK: ffff8fb033063d80  CPU: 20  COMMAND: "kworker/u97:451"
 0 [ffffb656ce1abc28] __schedule at ffffffff8be629e3
 1 [ffffb656ce1abcc8] schedule at ffffffff8be62fe8
 2 [ffffb656ce1abcd0] schedule_timeout at ffffffff8be671ed
 3 [ffffb656ce1abd70] wait_for_completion at ffffffff8be639cf
 4 [ffffb656ce1abdd0] flush_work at ffffffff8b6ce2d5
 5 [ffffb656ce1abe70] nvme_stop_ctrl at ffffffffc0144900 [nvme_core]
 6 [ffffb656ce1abe80] nvme_fc_reset_ctrl_work at ffffffffc0243445 [nvme_fc]
 7 [ffffb656ce1abe98] process_one_work at ffffffff8b6cd437
 8 [ffffb656ce1abed8] worker_thread at ffffffff8b6cdb50
 9 [ffffb656ce1abf10] kthread at ffffffff8b6d3402
10 [ffffb656ce1abf50] ret_from_fork at ffffffff8c000255

Link: https://lore.kernel.org/r/20200806111014.28434-10-njavali@marvell.com
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>