On Fri, 27 May 2016 10:10:59 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Fri 27-05-16 10:00:48, Arnd Bergmann wrote:
> > The change to the oom_reaper to hold a mutex inside __oom_reap_task()
> > accidentally started calling mmput_async() on the local
> > mm before that variable got initialized, as reported by gcc
> > in linux-next:
> >
> > mm/oom_kill.c: In function '__oom_reap_task':
> > mm/oom_kill.c:537:2: error: 'mm' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >
> > This rearranges the code slightly back to the state before patch
> > but leaves the lock in place. The error handling in the function
> > still looks a bit confusing and could probably be improved
> > but I could not come up with a solution that made me happy
> > for now.
> >
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > Fixes: mmotm ("oom_reaper: close race with exiting task")
>
> Thanks for catching that Arnd?
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
I think I preferred my version - all those unwinding return statements
can cause problems..
--- 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;
}
_
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