rcu: Use *_ONCE() to protect lockless ->expmask accesses
The rcu_node structure's ->expmask field is accessed locklessly when starting a new expedited grace period and when reporting an expedited RCU CPU stall warning. This commit therefore handles the former by taking a snapshot of ->expmask while the lock is held and the latter by applying READ_ONCE() to lockless reads and WRITE_ONCE() to the corresponding updates. Link: https://lore.kernel.org/lkml/CANpmjNNmSOagbTpffHr4=Yedckx9Rm2NuGqC9UqE+AOz5f1-ZQ@mail.gmail.com Reported-by:<syzbot+134336b86f728d6e55a0@syzkaller.appspotmail.com> Signed-off-by:
Paul E. McKenney <paulmck@kernel.org> Acked-by:
Marco Elver <elver@google.com>
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