This is a note to let you know that I've just added the patch titled include/linux/sched/mm.h: use rcu_dereference in in_vfork() to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: include-linux-sched-mm.h-use-rcu_dereference-in-in_v.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 16dd190ecf3f2a15f875c7ba42540b7d05e5cee6 Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Date: Fri Mar 12 21:08:03 2021 -0800 include/linux/sched/mm.h: use rcu_dereference in in_vfork() [ 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@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> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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;