Messages in this thread | | | From | Linus Torvalds <> | Date | Wed, 4 Sep 2019 11:20:03 -0700 | Subject | Re: [PATCH 1/3] task: Add a count of task rcu users |
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On Wed, Sep 4, 2019 at 9:33 AM Frederic Weisbecker <frederic@kernel.org> wrote: > > I thought the point of these rcu_users was to be able to do: > > rcu_read_lock() > p = rcu_dereference(task) > if (!refcount_inc_not_zero(p->rcu_users)) {
No. Because of the shared state, you can't do that from RCU context.
But you *could* increase rcu_users from within the process context itself (as long as you do it before the exit path, ie during normal system call execution), or possibly while holding the tasklist_lock and verifying that the task hasn't died yet.
I'm not sure there is any sensible case for doing that, though. It would have to have a similar pattern to the runqueue use, where you add a new RCU lookup point for the task. I'm sure something like that _could_ exist, I just can't think of any right now.
Linus
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