linux-kernel - [PATCH 2/3] percpu: acquire pcpu_lock when updating pcpu_nr_empty_pop

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Message-Id: <20170225210019.23610-1-tahsin@google.com>
Date:   Sat, 25 Feb 2017 13:00:19 -0800
From:   Tahsin Erdogan <tahsin@...gle.com>
To:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Roman Pen <r.peniaev@...il.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>, zijun_hu <zijun_hu@....com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Tahsin Erdogan <tahsin@...gle.com>
Subject: [PATCH 2/3] percpu: acquire pcpu_lock when updating pcpu_nr_empty_pop_pages

Update to pcpu_nr_empty_pop_pages in pcpu_alloc() is currently done
without holding pcpu_lock. This can lead to bad updates to the variable.
Add missing lock calls.

Fixes: b539b87fed37 ("percpu: implmeent pcpu_nr_empty_pop_pages and chunk->nr_populated")
Signed-off-by: Tahsin Erdogan <tahsin@...gle.com>
---
 mm/percpu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 0686f566d347..232356a2d914 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1011,8 +1011,11 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 		mutex_unlock(&pcpu_alloc_mutex);
 	}
 
-	if (chunk != pcpu_reserved_chunk)
+	if (chunk != pcpu_reserved_chunk) {
+		spin_lock_irqsave(&pcpu_lock, flags);
 		pcpu_nr_empty_pop_pages -= occ_pages;
+		spin_unlock_irqrestore(&pcpu_lock, flags);
+	}
 
 	if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
 		pcpu_schedule_balance_work();
-- 
2.11.0.483.g087da7b7c-goog