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include/linux/sched/mm.h: use rcu_dereference in in_vfork()

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[ 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: b18dc5f291 ("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>
This commit is contained in:
Matthew Wilcox (Oracle) 2021-03-12 21:08:03 -08:00 committed by Greg Kroah-Hartman
parent 7da7542c04
commit 3cbe8f9193
1 changed files with 2 additions and 1 deletions
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include/linux/sched/mm.h
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@ -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;