linux-kernel - Re: linux-next: build warning after merge of the akpm-current tree

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Date:	Fri, 27 May 2016 12:53:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...e.com>
Subject: Re: linux-next: build warning after merge of the akpm-current tree

On Fri, 27 May 2016 13:07:10 +1000 Stephen Rothwell <sfr@...b.auug.org.au> wrote:

> Hi Andrew,
> 
> After merging the akpm-current tree, today's linux-next build (arm
> multi_v7_defconfig) produced this warning:
> 
> mm/oom_kill.c: In function '__oom_reap_task':
> mm/oom_kill.c:537:2: warning: 'mm' may be used uninitialized in this function [-Wmaybe-uninitialized]
>   mmput_async(mm);
>   ^
> 
> Introduced by commit
> 
>   df1e2f56632d ("oom_reaper: close race with exiting task")
> 
> This is real - the first "goto unlock_oom" is before "mm" has been
> assigned.

Yup, thanks.

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: oom_reaper-close-race-with-exiting-task-fix

fix use of unused `mm', Per Stephen

Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/oom_kill.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff -puN mm/oom_kill.c~oom_reaper-close-race-with-exiting-task-fix mm/oom_kill.c
--- a/mm/oom_kill.c~oom_reaper-close-race-with-exiting-task-fix
+++ a/mm/oom_kill.c
@@ -443,7 +443,7 @@ static bool __oom_reap_task(struct task_
 {
 	struct mmu_gather tlb;
 	struct vm_area_struct *vma;
-	struct mm_struct *mm;
+	struct mm_struct *mm = NULL;
 	struct task_struct *p;
 	struct zap_details details = {.check_swap_entries = true,
 				      .ignore_dirty = true};
@@ -534,7 +534,8 @@ unlock_oom:
 	 * different context because we shouldn't risk we get stuck there and
 	 * put the oom_reaper out of the way.
 	 */
-	mmput_async(mm);
+	if (mm)
+		mmput_async(mm);
 	return ret;
 }
 
_