linux-kernel - [PATCH 7/9] mm/page_alloc: Explicitly acquire the zone lock in __free_pages

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Date:   Wed, 12 May 2021 10:54:56 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Chuck Lever <chuck.lever@...cle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-RT-Users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 7/9] mm/page_alloc: Explicitly acquire the zone lock in __free_pages_ok

__free_pages_ok() disables IRQs before calling a common helper
free_one_page() that acquires the zone lock. This is not safe according
to Documentation/locking/locktypes.rst and in this context, IRQ disabling
is not protecting a per_cpu_pages structure either or a local_lock would
be used.

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 <mgorman@...hsingularity.net>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5879b595b74b..7da70b404f4e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1579,21 +1579,21 @@ 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, fpi_flags))
 		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);
+	if (unlikely(has_isolate_pageblock(zone) ||
+		is_migrate_isolate(migratetype))) {
+		migratetype = get_pfnblock_migratetype(page, pfn);
+	}
+	__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