misc/sgi-xp: Replace in_interrupt() usage

The usage of in_interrupt() in xpc_partition_disengaged() is clearly
intended to avoid canceling the timeout timer when the function is invoked
from the timer callback.

While in_interrupt() is deprecated and ill defined as it does not provide
what the name suggests it catches the intended case.

Add an argument to xpc_partition_disengaged() which is true if called
from timer and otherwise false.
Use del_timer_sync() instead of del_singleshot_timer_sync() which is the
same thing.

Note: This does not prevent reentrancy into the function as the function
has no concurrency control and timer callback and regular task context
callers can happen concurrently on different CPUs or the timer can
interrupt the task context before it is able to cancel it.

While the only driver which is providing the arch_xpc_ops callbacks
(xpc_uv) seems not to have a reentrancy problem and the only negative
effect would be a double dev_info() entry in dmesg, the whole mechanism is
conceptually broken.

But that's not subject of this cleanup endeavour and left as an exercise to
the folks who might have interest to make that code fully correct.

[bigeasy: Add the argument, use del_timer_sync().]

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Cliff Whickman <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Robin Holt <[e-mail]>
Cc: Steve Wahl <[e-mail]>
Cc: Dimitri Sivanich <[e-mail]>
Cc: Russ Anderson <[e-mail]>
Reviewed-by: Steve Wahl <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/sgi-xp/xpc.h

···
 extern void xpc_teardown_rsvd_page(void);
 extern int xpc_identify_activate_IRQ_sender(void);
 extern int xpc_partition_disengaged(struct xpc_partition *);
+extern int xpc_partition_disengaged_from_timer(struct xpc_partition *part);
 extern enum xp_retval xpc_mark_partition_active(struct xpc_partition *);
 extern void xpc_mark_partition_inactive(struct xpc_partition *);
 extern void xpc_discovery(void);

drivers/misc/sgi-xp/xpc_main.c

···
 
 	DBUG_ON(time_is_after_jiffies(part->disengage_timeout));
 
-	(void)xpc_partition_disengaged(part);
+	xpc_partition_disengaged_from_timer(part);
 
 	DBUG_ON(part->disengage_timeout != 0);
 	DBUG_ON(xpc_arch_ops.partition_engaged(XPC_PARTID(part)));

drivers/misc/sgi-xp/xpc_partition.c

···
  * from us. Though we requested the remote partition to deactivate with regard
  * to us, we really only need to wait for the other side to disengage from us.
  */
-int
-xpc_partition_disengaged(struct xpc_partition *part)
+static int __xpc_partition_disengaged(struct xpc_partition *part,
+				      bool from_timer)
 {
 	short partid = XPC_PARTID(part);
 	int disengaged;
···
 		}
 		part->disengage_timeout = 0;
 
-		/* cancel the timer function, provided it's not us */
-		if (!in_interrupt())
-			del_singleshot_timer_sync(&part->disengage_timer);
+		/* Cancel the timer function if not called from it */
+		if (!from_timer)
+			del_timer_sync(&part->disengage_timer);
 
 		DBUG_ON(part->act_state != XPC_P_AS_DEACTIVATING &&
 			part->act_state != XPC_P_AS_INACTIVE);
···
 		xpc_arch_ops.cancel_partition_deactivation_request(part);
 	}
 	return disengaged;
+}
+
+int xpc_partition_disengaged(struct xpc_partition *part)
+{
+	return __xpc_partition_disengaged(part, false);
+}
+
+int xpc_partition_disengaged_from_timer(struct xpc_partition *part)
+{
+	return __xpc_partition_disengaged(part, true);
 }
 
 /*