[PATCH] mm: cleanup balance_dirty_pages() that leave variables uninitialized

[PATCH] mm: cleanup balance_dirty_pages() that leave variables uninitialized

[Liao Tonglang]

Variables m_thresh and m_dirty in function balance_dirty_pages() may use
uninitialized. GCC throws a warning on it. Fixed by assigned to 0 as
initial value.

Signed-off-by: Liao Tonglang <liaotonglang@gmail.com>
---
 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 0a931cd..288db45 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1534,7 +1534,7 @@ 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;
 
 		/*
 		 * Unstable writes are a feature of certain networked
-- 
1.8.3.1

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Re: [PATCH] mm: cleanup balance_dirty_pages() that leave variables uninitialized

[Jan Kara]

On Mon 12-10-15 20:24:58, Liao Tonglang wrote:
> Variables m_thresh and m_dirty in function balance_dirty_pages() may use
> uninitialized. GCC throws a warning on it. Fixed by assigned to 0 as
> initial value.

The code is correct - m_dirty & m_thresh gets set & used only if mdtc is
set. So the warning is false positive (and e.g. my gcc doesn't warn). What
gcc version are you using?

								Honza

> 
> Signed-off-by: Liao Tonglang <liaotonglang@gmail.com>
> ---
>  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 0a931cd..288db45 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1534,7 +1534,7 @@ 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;
>  
>  		/*
>  		 * Unstable writes are a feature of certain networked
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH] mm: cleanup balance_dirty_pages() that leave variables uninitialized

[Liao Tonglang]

On 2015/10/12 20:58, Jan Kara wrote:
> What
> gcc version are you using?
It is the last line of my gcc -v command.
     gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC)
And it warn like this:
mm/page-writeback.c: In function ?balance_dirty_pages.isra.26?:
mm/page-writeback.c:1537:26: warning: ?m_thresh? may be used 
uninitialized in this function [-Wmaybe-uninitialized]
    unsigned long m_dirty, m_thresh, m_bg_thresh;
                           ^
mm/page-writeback.c:1537:17: warning: ?m_dirty? may be used 
uninitialized in this function [-Wmaybe-uninitialized]
    unsigned long m_dirty, m_thresh, m_bg_thresh;
                  ^

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