From: Greg Kroah-Hartman gregkh@linuxfoundation.org
From: Matthew Wilcox (Oracle) willy@infradead.org
[ Upstream commit 149fc787353f65b7e72e05e7b75d34863266c3e2 ]
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.
Link: https://lkml.kernel.org/r/20210221194207.1351703-1-willy@infradead.org Fixes: b18dc5f291c0 ("mm, oom: skip vforked tasks from being selected") Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Reviewed-by: Miaohe Lin linmiaohe@huawei.com Acked-by: Michal Hocko mhocko@suse.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 a132d875d351..3a1d899019af 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -167,7 +167,8 @@ 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;