On Wednesday 10 September 2014 11:50:41 David Rientjes wrote:
> On Wed, 10 Sep 2014, Xiubo Li wrote:
>
> > C mm/compaction.o
> > mm/compaction.c: In function isolate_freepages_block:
> > mm/compaction.c:364:37: warning: flags may be used uninitialized in
> > this function [-Wmaybe-uninitialized]
> > && compact_unlock_should_abort(&cc->zone->lock, flags,
> > ^
> > In file included from include/linux/irqflags.h:15:0,
> > from ./arch/arm/include/asm/bitops.h:27,
> > from include/linux/bitops.h:33,
> > from include/linux/kernel.h:10,
> > from include/linux/list.h:8,
> > from include/linux/preempt.h:10,
> > from include/linux/spinlock.h:50,
> > from include/linux/swap.h:4,
> > from mm/compaction.c:10:
> > mm/compaction.c: In function isolate_migratepages_block:
> > ./arch/arm/include/asm/irqflags.h:152:2: warning: flags may be used
> > uninitialized in this function [-Wmaybe-uninitialized]
> > asm volatile(
> > ^
> > mm/compaction.c:576:16: note: flags as declared here
> > unsigned long flags;
> > ^
> >
> > Signed-off-by: Xiubo Li <Li.Xiubo@xxxxxxxxxxxxx>
>
> Arnd Bergmann already sent a patch for this to use uninitialized_var()
> privately but it didn't get cc'd to any mailing list, sorry.
Oops, I hadn't noticed that I missed the mailing lists, sorry about that.
For reference, see my patch below.
Arnd
8<------
>From a89cbd7a79d3ee0d35209416ea9bf35d4d2a8e69 Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@xxxxxxxx>
Date: Mon, 8 Sep 2014 12:25:14 +0200
Subject: [PATCH] mm: compaction: fix compile warning
The recently changed code in isolate_freepages_block seems to confuse
gcc-4.9 to the point where it can't know whether the 'flags' variable
is used or not. This happens for me with e.g. ARM realview_defconfig,
but not other configurations:
mm/compaction.c: In function 'isolate_freepages_block':
mm/compaction.c:364:10: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
&& compact_unlock_should_abort(&cc->zone->lock, flags,
^
In file included from include/linux/irqflags.h:15:0,
from arch/arm/include/asm/bitops.h:27,
from include/linux/bitops.h:33,
from include/linux/kernel.h:10,
from include/linux/list.h:8,
from include/linux/preempt.h:10,
from include/linux/spinlock.h:50,
from include/linux/swap.h:4,
from mm/compaction.c:10:
mm/compaction.c: In function 'isolate_migratepages_block':
arch/arm/include/asm/irqflags.h:152:2: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
asm volatile(
^
mm/compaction.c:576:16: note: 'flags' was declared here
unsigned long flags;
Using the uninitialized_var() macro is probably not the best solution,
but it shuts up the warning.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: 142d94959e41 ("mm, compaction: periodically drop lock and restore IRQs in scanners")
diff --git a/mm/compaction.c b/mm/compaction.c
index 7d9d92e63297..1e22b46a9690 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -344,7 +344,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
{
int nr_scanned = 0, total_isolated = 0;
struct page *cursor, *valid_page = NULL;
- unsigned long flags;
+ unsigned long uninitialized_var(flags);
bool locked = false;
unsigned long blockpfn = *start_pfn;
@@ -573,7 +573,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
unsigned long nr_scanned = 0, nr_isolated = 0;
struct list_head *migratelist = &cc->migratepages;
struct lruvec *lruvec;
- unsigned long flags;
+ unsigned long uninitialized_var(flags);
bool locked = false;
struct page *page = NULL, *valid_page = NULL;
--
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