mm: compaction: move fatal signal check out of compact_checklock_irqsave

Commit c67fe3752abe ("mm: compaction: Abort async compaction if locks
are contended or taking too long") addressed a lock contention problem
in compaction by introducing compact_checklock_irqsave() that effecively
aborting async compaction in the event of compaction.

To preserve existing behaviour it also moved a fatal_signal_pending()
check into compact_checklock_irqsave() but that is very misleading.  It
"hides" the check within a locking function but has nothing to do with
locking as such.  It just happens to work in a desirable fashion.

This patch moves the fatal_signal_pending() check to
isolate_migratepages_range() where it belongs.  Arguably the same check
should also happen when isolating pages for freeing but it's overkill.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -75,8 +75,6 @@ static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
 		}
 
 		cond_resched();
-		if (fatal_signal_pending(current))
-			return false;
 	}
 
 	if (!locked)
@@ -363,7 +361,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 		/* Check if it is ok to still hold the lock */
 		locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
 								locked, cc);
-		if (!locked)
+		if (!locked || fatal_signal_pending(current))
 			break;
 
 		/*