iscsi-scst: Measure shutdown grace from the start of the wait

The saved pre-fix Cppcheck log reports:

  iscsi-scst/kernel/nthread.c:326: style:
  Clarify calculation precedence for '+' and '?'. [clarifyCalculation]

close_conn calculates its shutdown deadline with this expression:

  shut_start_waiting + conn->deleting ? CONN_DEL_SHUT_TIMEOUT :
                                      CONN_REG_SHUT_TIMEOUT

Addition binds more tightly than the conditional operator. The expression
therefore tests shut_start_waiting + conn->deleting and selects an
absolute 10- or 125-second jiffies value, rather than adding an interval
to the start timestamp. On a host with sufficient uptime, the transport
can be closed immediately after shutdown starts.

Select the interval first, add it to shut_start_waiting, and retain the
wrap-safe time_after comparison. Move the check into a private helper so
its timing behavior can be covered without a live connection.

Add KUnit coverage for both deletion and normal shutdown, high uptime,
the ticks before/at/after expiry and jiffies wraparound. The tests retain
the original strict-after deadline convention.

iscsi-scst/kernel/kunit/suites/iscsi_close_test.c

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/jiffies.h>
+#ifdef INSIDE_KERNEL_TREE
+#include "../../../kunit/scst_kunit.h"
+#else
+#include "../../../../scst/src/kunit/scst_kunit.h"
+#endif
+#include "../../iscsi_trace_flag.h"
+#include "../../iscsi.h"
+#include "../../nthread_test.h"
+
+static void iscsi_shutdown_grace_period(struct kunit *test)
+{
+	static const unsigned long starts[] = { 10000UL * HZ, ULONG_MAX - 5UL * HZ };
+	unsigned int i, deleting;
+
+	for (i = 0; i < ARRAY_SIZE(starts); i++) {
+		for (deleting = 0; deleting <= 1; deleting++) {
+			unsigned long grace = deleting ? 10UL * HZ : 125UL * HZ;
+			unsigned long started = starts[i];
+			bool expired;
+
+			/* A close starts a relative deadline, independent of uptime. */
+			expired = iscsi_shutdown_timed_out(deleting, started, started);
+			KUNIT_EXPECT_FALSE(test, expired);
+			expired = iscsi_shutdown_timed_out(deleting, started, started + grace - 1);
+			KUNIT_EXPECT_FALSE(test, expired);
+			expired = iscsi_shutdown_timed_out(deleting, started, started + grace);
+			KUNIT_EXPECT_FALSE(test, expired);
+			expired = iscsi_shutdown_timed_out(deleting, started, started + grace + 1);
+			KUNIT_EXPECT_TRUE(test, expired);
+		}
+	}
+}
+
+static struct kunit_case iscsi_close_cases[] = {
+	KUNIT_CASE(iscsi_shutdown_grace_period),
+	{}
+};
+
+scst_kunit_suite(iscsi_close_suite, "ISCSI", "-close",
+		 .test_cases = iscsi_close_cases,
+);

iscsi-scst/kernel/nthread.c

@@ -210,6 +210,18 @@ void iscsi_task_mgmt_affected_cmds_done(struct scst_mgmt_cmd *scst_mcmd)
 	}
 }
 
+#define CONN_PENDING_TIMEOUT	((typeof(jiffies))10 * HZ)
+#define CONN_WAIT_TIMEOUT	((typeof(jiffies))10 * HZ)
+#define CONN_REG_SHUT_TIMEOUT	((typeof(jiffies))125 * HZ)
+#define CONN_DEL_SHUT_TIMEOUT	((typeof(jiffies))10 * HZ)
+
+SCST_KUNIT_VISIBLE
+bool iscsi_shutdown_timed_out(bool deleting, unsigned long started, unsigned long now)
+{
+	return time_after(now, started +
+			  (deleting ? CONN_DEL_SHUT_TIMEOUT : CONN_REG_SHUT_TIMEOUT));
+}
+
 /* No locks */
 static void close_conn(struct iscsi_conn *conn)
 {
@@ -223,11 +235,6 @@ static void close_conn(struct iscsi_conn *conn)
 	int rc;
 	int lun = 0;
 
-#define CONN_PENDING_TIMEOUT	((typeof(jiffies))10 * HZ)
-#define CONN_WAIT_TIMEOUT	((typeof(jiffies))10 * HZ)
-#define CONN_REG_SHUT_TIMEOUT	((typeof(jiffies))125 * HZ)
-#define CONN_DEL_SHUT_TIMEOUT	((typeof(jiffies))10 * HZ)
-
 	TRACE_ENTRY();
 
 	TRACE_MGMT_DBG("Closing connection %p (conn_ref_cnt=%d)",
@@ -322,9 +329,7 @@ static void close_conn(struct iscsi_conn *conn)
 		}
 
 		if (wait_expired && !shut_expired &&
-		    time_after(jiffies, shut_start_waiting +
-				conn->deleting ? CONN_DEL_SHUT_TIMEOUT :
-						 CONN_REG_SHUT_TIMEOUT)) {
+		    iscsi_shutdown_timed_out(conn->deleting, shut_start_waiting, jiffies)) {
 			TRACE_CONN_CLOSE("Wait time after shutdown expired (conn %p)",
 					 conn);
 			conn->transport->iscsit_conn_close(conn, 0);

iscsi-scst/kernel/nthread_test.h

@@ -14,6 +14,7 @@ int write_data(struct iscsi_conn *conn);
 int iscsi_tx_sendmsg(struct socket *sock, struct msghdr *msg,
 		     struct kvec *iov, size_t size);
 void iscsi_tx_complete(struct iscsi_cmnd *cmnd);
+bool iscsi_shutdown_timed_out(bool deleting, unsigned long started, unsigned long now);
 
 #endif /* SCST_KUNIT_ENABLED */
 #endif /* SCST_ISCSI_NTHREAD_TEST_H */

scst/src/kunit/objects.mk

@@ -20,6 +20,7 @@ scst-kunit-scst := \
 	kunit/unmap/suites/scst_kunit_unmap.o
 
 scst-kunit-iscsi-scst := \
+	kunit/suites/iscsi_close_test.o \
 	kunit/suites/iscsi_tx_test.o
 
 scst-kunit-qla2x00tgt := \