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From:   Mel Gorman <mgorman@techsingularity.net>
To:     Linux-MM <linux-mm@kvack.org>,
        Linux-RT-Users <linux-rt-users@vger.kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 09/11] mm/page_alloc: Explicitly acquire the zone lock in __free_pages_ok
Date:   Wed,  7 Apr 2021 21:24:21 +0100
Message-Id: <20210407202423.16022-10-mgorman@techsingularity.net>
In-Reply-To: <20210407202423.16022-1-mgorman@techsingularity.net>
References: <20210407202423.16022-1-mgorman@techsingularity.net>
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__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 <mgorman@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