linux-kernel - Re: [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys

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Date:   Fri, 1 Feb 2019 13:15:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     mingo@...hat.com, tj@...nel.org, longman@...hat.com,
        johannes.berg@...el.com, linux-kernel@...r.kernel.org,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys

On Fri, Jan 18, 2019 at 06:34:20PM -0800, Bart Van Assche wrote:

> I agree with what you wrote. The only code I know of that accesses list
> entries using RCU is the __bfs() function. In that function I found the
> following loop:
> 
> 	list_for_each_entry_rcu(entry, head, entry) { [ ... ] }

Thing is; I can't seem to find any __bfs() usage outside of graph_lock.

  count_{fwd,bwd}_deps() - takes graph lock

  check_{noncircular,redudant}() - called from check_prev_add() <-
  check_prevs_add() <- validate_chain() which takes graph lock

  find_usage{,_fwd,_bwd}
    <- check_usage() <- check_irq_usage() <- check_prev_add_irq() <-
    check_prev_add <- check_prevs_add() <- validate_chain() which takes
    graph lock

    <- check_usage_{fwd,bdw}() <- mark_lock_irq() <- mark_lock() which
    takes graph lock

Or did I miss something? If there are no __bfs() users outside of graph
lock, then we can simply remove that _rcu from the iteration, and
simplify all that.

> Since zap_class() calls list_del_rcu(&entry->entry), since a grace period
> occurs between the call_rcu() invocation and the RCU callback function,
> since at least an RCU reader lock must be held around RCU loops and since
> sleeping is not allowed while holding an RCU read lock I think there is
> no risk that __bfs() will examine a list entry after it has been freed.

So you agree that list_entry_being_freed() should only check the current
pf?



Also; yes, I seem to have completely misplaced your #14, I've not idea
how I totally lost one patch, that was certainly not intentional, sorry
about that.