[PATCH 14/33] scsi: qla2xxx: Fix soft lockup polling continuation IOCB signature

qla27xx_copy_multiple_pkt() and qla27xx_copy_fpin_pkt() poll
rsp_q->ring_ptr->signature for RESPONSE_PROCESSED (0xDEADDEAD) to decide
whether the next continuation IOCB has arrived, spinning on cpu_relax()
without advancing the ring or decrementing the entry count while it has
not. response_t::signature lives at byte offset 60, but a continuation
IOCB (sts_cont_entry_t / struct sts_cont_entry_ext) carries raw FC frame
payload at that offset (data[56..59]). A received frame whose payload
bytes happen to equal 0xDEADDEAD is therefore misread as "not yet
arrived", and the loop spins forever in interrupt/DPC context, causing a
CPU soft lockup.

The poll is also unnecessary: callers of qla27xx_copy_multiple_pkt()
(PT_LS4_UNSOL and the NVMe purls path) already gate on
qla_chk_cont_iocb_avail(), which guarantees all entry_count IOCBs are
present before copying begins. The sibling helper
__qla_copy_purex_to_buffer() already drops the signature poll and relies
on the entry_type == STATUS_CONT_TYPE guard instead.

Remove the signature busy-wait from both helpers, keeping the entry_type
guard, and gate the FPIN path with qla_chk_cont_iocb_avail() so it defers
and re-processes on the next interrupt once all continuation IOCBs have
arrived, mirroring the ELS_AUTH_ELS and PT_LS4_UNSOL arms. With this the
signature field is never read on a continuation IOCB, eliminating the
payload-aliasing lockup.

Fixes: 9f2475fe7406 ("scsi: qla2xxx: SAN congestion management implementation")
Cc: [email protected]
Reported-by: Sashiko <[email protected]>
Signed-off-by: Nilesh Javali <[email protected]>
---
 drivers/scsi/qla2xxx/qla_isr.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/drivers/scsi/qla2xxx/qla_isr.c b/drivers/scsi/qla2xxx/qla_isr.c
index 6375c18fe392..d9019f2b059c 100644
--- a/drivers/scsi/qla2xxx/qla_isr.c
+++ b/drivers/scsi/qla2xxx/qla_isr.c
@@ -1002,14 +1002,6 @@ qla27xx_copy_multiple_pkt(struct scsi_qla_host *vha, void **pkt,
 
 	do {
 		while ((total_bytes > 0) && (entry_count_remaining > 0)) {
-			if (rsp_q->ring_ptr->signature == RESPONSE_PROCESSED) {
-				ql_dbg(ql_dbg_async, vha, 0x5084,
-				       "Ran out of IOCBs, partial data 0x%x\n",
-				       buffer_copy_offset);
-				cpu_relax();
-				continue;
-			}
-
 			*pkt = rsp_q->ring_ptr;
 			data = ((sts_cont_entry_t *)*pkt)->data;
 			data_sz = qla_sts_cont_data_size(ha);
@@ -1299,14 +1291,6 @@ qla27xx_copy_fpin_pkt(struct scsi_qla_host *vha, void **pkt,
 
 	do {
 		while ((total_bytes > 0) && (entry_count_remaining > 0)) {
-			if (rsp_q->ring_ptr->signature == RESPONSE_PROCESSED) {
-				ql_dbg(ql_dbg_async, vha, 0x5084,
-				       "Ran out of IOCBs, partial data 0x%x\n",
-				       buffer_copy_offset);
-				cpu_relax();
-				continue;
-			}
-
 			*pkt = rsp_q->ring_ptr;
 			data = ((sts_cont_entry_t *)*pkt)->data;
 			data_sz = qla_sts_cont_data_size(ha);
@@ -4272,9 +4256,24 @@ void qla24xx_process_response_queue(struct scsi_qla_host *vha,
 					       "SCM not active for this port\n");
 					break;
 				}
+				if (qla_chk_cont_iocb_avail(vha, rsp,
+				    (response_t *)pkt, rsp_in)) {
+					/*
+					 * ring_ptr and ring_index were
+					 * pre-incremented above. Reset them
+					 * back to current. Wait for next
+					 * interrupt with all IOCBs to arrive
+					 * and re-process.
+					 */
+					qla_rsp_ring_rewind_to(rsp,
+					    (response_t *)pkt, cur_ring_index);
+
+					ql_dbg(ql_dbg_init, vha, 0x5095,
+					    "Defer processing FPIN...\n");
+					return;
+				}
 				pure_item = qla27xx_copy_fpin_pkt(vha,
 							  (void **)&pkt, &rsp);
-				__update_rsp_in(is_shadow_hba, rsp, rsp_in);
 				if (!pure_item)
 					break;
 				qla24xx_queue_purex_item(vha, pure_item,
-- 
2.47.3