From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: include/linux/sched/mm.h: use rcu_dereference in in_vfork() 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@xxxxxxxxxxxxx Fixes: b18dc5f291c0 ("mm, oom: skip vforked tasks from being selected") Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/sched/mm.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/include/linux/sched/mm.h~mm-use-rcu_dereference-in-in_vfork +++ a/include/linux/sched/mm.h @@ -140,7 +140,8 @@ static inline bool in_vfork(struct task_ * 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; _
