[PATCH] writeback: initialize m_dirty to avoid compile warning

[Yang Shi]

When building kernel with gcc 5.2, the below warning is raised:

mm/page-writeback.c: In function 'balance_dirty_pages.isra.10':
mm/page-writeback.c:1545:17: warning: 'm_dirty' may be used uninitialized in this function [-Wmaybe-uninitialized]
   unsigned long m_dirty, m_thresh, m_bg_thresh;

The m_dirty{thresh, bg_thresh} are initialized in the block of "if (mdtc)",
so if mdts is null, they won't be initialized before being used.
Initialize m_dirty to zero, also initialize m_thresh and m_bg_thresh to keep
consistency.

They are used later by if condition:
!mdtc || m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh)

If mdtc is null, dirty_freerun_ceiling will not be called at all, so the
initialization will not change any behavior other than just ceasing the compile
warning.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx>
---
 mm/page-writeback.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2c90357..ce726eb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1542,7 +1542,7 @@ static void balance_dirty_pages(struct address_space *mapping,
 	for (;;) {
 		unsigned long now = jiffies;
 		unsigned long dirty, thresh, bg_thresh;
-		unsigned long m_dirty, m_thresh, m_bg_thresh;
+		unsigned long m_dirty = 0, m_thresh = 0, m_bg_thresh = 0;
 
 		/*
 		 * Unstable writes are a feature of certain networked
-- 
2.0.2

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