[PATCH 2/3] percpu: acquire pcpu_lock when updating pcpu_nr_empty_pop_pages

[Tahsin Erdogan]

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 <tah...@google.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