On Fri 27-05-16 12:55:34, Andrew Morton wrote:
> 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..
looks good to me as well.
Thanks!
> --- 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;
> }
>
> _
--
Michal Hocko
SUSE Labs
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