From: Christoph Lameter <clameter@engr.sgi.com>

Make release_pages(), __pagevec_lru_add() and __pagevec_lru_active()
preserve irq status

The swap migration code calls drain_lru_pages() to be able to push pages
off the LRU in order to cleanly remove a page from the LRU.  It uses
smp_call_function() for this purpose which uses IPIs to notify other
processors.  On IA64 IPIs are processes with enabled interrupts.  However,
other architectures like x86_64, i386 and powerpc keep the interrupts
disabled during IPI processing.  One solution would be to verify that these
platforms also allow the enabling of interrupts during IPIs but there is
f.e.  a plethora of methods to send IPIs under i386 that may make that
endeavor difficult.

This patch makes the functions called in mm/swap.c preserve the interrupt
state so that it is safe to call drain_lru_pages() during IPI on all
platforms.

The preservation of the interrupt state may allow the functions to be used
in other contexts in the future.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 mm/swap.c |   28 ++++++++++++++++------------
 1 files changed, 16 insertions(+), 12 deletions(-)

diff -puN mm/swap.c~preserve-irq-status-in-release_pages-__pagevec_lru_add mm/swap.c
--- devel/mm/swap.c~preserve-irq-status-in-release_pages-__pagevec_lru_add	2005-11-16 18:37:12.000000000 -0800
+++ devel-akpm/mm/swap.c	2005-11-16 18:37:12.000000000 -0800
@@ -102,15 +102,16 @@ int rotate_reclaimable_page(struct page 
 void fastcall activate_page(struct page *page)
 {
 	struct zone *zone = page_zone(page);
+	unsigned long flags;
 
-	spin_lock_irq(&zone->lru_lock);
+	spin_lock_irqsave(&zone->lru_lock, flags);
 	if (PageLRU(page) && !PageActive(page)) {
 		del_page_from_inactive_list(zone, page);
 		SetPageActive(page);
 		add_page_to_active_list(zone, page);
 		inc_page_state(pgactivate);
 	}
-	spin_unlock_irq(&zone->lru_lock);
+	spin_unlock_irqrestore(&zone->lru_lock, flags);
 }
 
 /*
@@ -209,6 +210,7 @@ void release_pages(struct page **pages, 
 	int i;
 	struct pagevec pages_to_free;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	pagevec_init(&pages_to_free, cold);
 	for (i = 0; i < nr; i++) {
@@ -221,15 +223,15 @@ void release_pages(struct page **pages, 
 		pagezone = page_zone(page);
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestClearPageLRU(page))
 			del_page_from_lru(zone, page);
 		if (page_count(page) == 0) {
 			if (!pagevec_add(&pages_to_free, page)) {
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 				__pagevec_free(&pages_to_free);
 				pagevec_reinit(&pages_to_free);
 				zone = NULL;	/* No lock is held */
@@ -237,7 +239,7 @@ void release_pages(struct page **pages, 
 		}
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 
 	pagevec_free(&pages_to_free);
 }
@@ -291,6 +293,7 @@ void __pagevec_lru_add(struct pagevec *p
 {
 	int i;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
@@ -298,16 +301,16 @@ void __pagevec_lru_add(struct pagevec *p
 
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
 		add_page_to_inactive_list(zone, page);
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }
@@ -318,6 +321,7 @@ void __pagevec_lru_add_active(struct pag
 {
 	int i;
 	struct zone *zone = NULL;
+	unsigned long flags = 0;	/* GCC warning */
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
@@ -325,9 +329,9 @@ void __pagevec_lru_add_active(struct pag
 
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irq(&zone->lru_lock);
+				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
-			spin_lock_irq(&zone->lru_lock);
+			spin_lock_irqsave(&zone->lru_lock, flags);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
@@ -336,7 +340,7 @@ void __pagevec_lru_add_active(struct pag
 		add_page_to_active_list(zone, page);
 	}
 	if (zone)
-		spin_unlock_irq(&zone->lru_lock);
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }
_