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SubjectRe: [PATCH] mm: Use rcu_dereference in in_vfork
On Sun 21-02-21 19:42:06, Matthew Wilcox wrote:
> Fix a sparse warning by using rcu_dereference(). Technically this is a
> bug and a sufficiently aggressive compiler could reload the `real_parent'
> pointer outside the protection of the rcu lock (and access freed memory),
> but I think it's pretty unlikely to happen.
>
> Fixes: b18dc5f291c0 ("mm, oom: skip vforked tasks from being selected")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

I must have missed the RCU part.
Thanks!

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> include/linux/sched/mm.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 1ae08b8462a4..90b2a0bce11c 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -140,7 +140,8 @@ static inline bool in_vfork(struct task_struct *tsk)
> * another oom-unkillable task does this it should blame itself.
> */
> rcu_read_lock();
> - ret = tsk->vfork_done && tsk->real_parent->mm == tsk->mm;
> + ret = tsk->vfork_done &&
> + rcu_dereference(tsk->real_parent)->mm == tsk->mm;
> rcu_read_unlock();
>
> return ret;
> --
> 2.29.2
>

--
Michal Hocko
SUSE Labs

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