Target de-configuration panics at high CPU load because TPGT and WWPN can
be removed on separate threads.

TPGT removal requests a reset HBA on a separate thread and waits for reset
complete (phase1). Due to high CPU load that HBA reset can be delayed for
some time.

WWPN removal does qlt_stop_phase2(). There it is believed that phase1 has
already completed and thus tgt.tgt_ops is subsequently cleared. However,
tgt.tgt_ops is needed to process incoming traffic and therefore this will
cause one of the following panics:

NIP qlt_reset+0x7c/0x220 [qla2xxx]
LR  qlt_reset+0x68/0x220 [qla2xxx]
Call Trace:
0xc000003ffff63a78 (unreliable)
qlt_handle_imm_notify+0x800/0x10c0 [qla2xxx]
qlt_24xx_atio_pkt+0x208/0x590 [qla2xxx]
qlt_24xx_process_atio_queue+0x33c/0x7a0 [qla2xxx]
qla83xx_msix_atio_q+0x54/0x90 [qla2xxx]

or

NIP qlt_24xx_handle_abts+0xd0/0x2a0 [qla2xxx]
LR  qlt_24xx_handle_abts+0xb4/0x2a0 [qla2xxx]
Call Trace:
qlt_24xx_handle_abts+0x90/0x2a0 [qla2xxx] (unreliable)
qlt_24xx_process_atio_queue+0x500/0x7a0 [qla2xxx]
qla83xx_msix_atio_q+0x54/0x90 [qla2xxx]

or

NIP qlt_create_sess+0x90/0x4e0 [qla2xxx]
LR  qla24xx_do_nack_work+0xa8/0x180 [qla2xxx]
Call Trace:
0xc0000000348fba30 (unreliable)
qla24xx_do_nack_work+0xa8/0x180 [qla2xxx]
qla2x00_do_work+0x674/0xbf0 [qla2xxx]
qla2x00_iocb_work_fn

The patch fixes the issue by serializing qlt_stop_phase1() and
qlt_stop_phase2() functions to make WWPN removal wait for phase1
completion.

Link: https://lore.kernel.org/r/20210415203554.27890-1-d.bogdanov@yadro.com


Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>