[PATCH 09/11] mm/page_alloc: Explicitly acquire the zone lock in __free_pages_ok

[Mel Gorman]

__free_pages_ok() disables IRQs before calling a common helper
free_one_page() that acquires the zone lock. While this is safe, it
unnecessarily disables IRQs on PREEMPT_RT kernels.

This patch explicitly acquires the lock with spin_lock_irqsave instead of
relying on a helper. This removes the last instance of local_irq_save()
in page_alloc.c.

Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
 mm/page_alloc.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1bb5b522a0f9..d94ec53367bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1559,21 +1559,18 @@ static void __free_pages_ok(struct page *page, unsigned 
int order,
        unsigned long flags;
        int migratetype;
        unsigned long pfn = page_to_pfn(page);
+       struct zone *zone = page_zone(page);
 
        if (!free_pages_prepare(page, order, true))
                return;
 
        migratetype = get_pfnblock_migratetype(page, pfn);
 
-       /*
-        * TODO FIX: Disable IRQs before acquiring IRQ-safe zone->lock
-        * and protect vmstat updates.
-        */
-       local_irq_save(flags);
+       spin_lock_irqsave(&zone->lock, flags);
        __count_vm_events(PGFREE, 1 << order);
-       free_one_page(page_zone(page), page, pfn, order, migratetype,
-                     fpi_flags);
-       local_irq_restore(flags);
+       migratetype = check_migratetype_isolated(zone, page, pfn, migratetype);
+       __free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
+       spin_unlock_irqrestore(&zone->lock, flags);
 }
 
 void __free_pages_core(struct page *page, unsigned int order)
-- 
2.26.2