On 2018/06/27 8:50, Paul E. McKenney wrote: > On Wed, Jun 27, 2018 at 05:10:48AM +0900, Tetsuo Handa wrote: >> As far as I can see, >> >> - atomic_set(&oom_callback_count, 1); >> + atomic_inc(&oom_callback_count); >> >> should be sufficient. > > I don't see how that helps. For example, suppose that two tasks > invoked rcu_oom_notify() at about the same time. Then they could > both see oom_callback_count equal to zero, both atomically increment > oom_callback_count, then both do the IPI invoking rcu_oom_notify_cpu() > on each online CPU. > > So far, so good. But rcu_oom_notify_cpu() enqueues a per-CPU RCU > callback, and enqueuing the same callback twice in quick succession > would fatally tangle RCU's callback lists. > > What am I missing here? > > Thanx, Paul
You are pointing out that "number of rsp->call() is called" > "number of rcu_oom_callback() is called" can happen if concurrently called, aren't you? Then, you are not missing anything. You will need to use something equivalent to oom_lock even if you can convert rcu_oom_notify() to use shrinkers.
