From: Peter Zijlstra <peterz@infradead.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: mingo@redhat.com, tj@kernel.org, longman@redhat.com,
johannes.berg@intel.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys
Date: Fri, 11 Jan 2019 17:55:29 +0100 [thread overview]
Message-ID: <20190111165529.GA14054@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <1547222103.83374.72.camel@acm.org>
On Fri, Jan 11, 2019 at 07:55:03AM -0800, Bart Van Assche wrote:
> On Fri, 2019-01-11 at 13:48 +0100, Peter Zijlstra wrote:
> > I spotted this new v6 in my inbox and have rebased to it.
>
> Thanks!
>
> > On Wed, Jan 09, 2019 at 01:01:48PM -0800, Bart Van Assche wrote:
> >
> > > The changes compared to v5 are:
> > > - Modified zap_class() such that it doesn't try to free a list entry that
> > > is already being freed.
> >
> > I however have a question on this; this seems wrong. Once a list entry
> > is enqueued it should not be reachable anymore. If we can reach an entry
> > after call_rcu() happened, we've got a problem.
>
> Apparently I confused you - sorry that I was not more clear. What I meant is
> that I changed a single if test into a loop. The graph lock is held while that
> loop is being executed so the code below is serialized against the code called
> from inside the RCU callback:
>
> @@ -4574,8 +4563,9 @@ static void zap_class(struct pending_free *pf, struct lock
> _class *class)
> entry = list_entries + i;
> if (entry->class != class && entry->links_to != class)
> continue;
> - if (__test_and_set_bit(i, pf->list_entries_being_freed))
> + if (list_entry_being_freed(i))
> continue;
Yes, it is the above change that caught my eye.. That checks _both_ your
lists. One is your current open one (@pf), but the other could already
be pending the call_rcu().
So my question is why do we have to check both ?! How come the old code,
that only checked @pf, is wrong?
> + set_bit(i, pf->list_entries_being_freed);
> nr_list_entries--;
> list_del_rcu(&entry->entry);
> }
>
> Please let me know if you need more information.
>
> Bart.
>
next prev parent reply other threads:[~2019-01-11 16:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 21:01 [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 01/16] locking/lockdep: Fix reported required memory size Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 02/16] locking/lockdep: Avoid that add_chain_cache() adds an invalid chain to the cache Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 03/16] locking/lockdep: Make zap_class() remove all matching lock order entries Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 04/16] locking/lockdep: Reorder struct lock_class members Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 05/16] locking/lockdep: Initialize the locks_before and locks_after lists earlier Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 06/16] locking/lockdep: Split lockdep_free_key_range() and lockdep_reset_lock() Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 07/16] locking/lockdep: Make it easy to detect whether or not inside a selftest Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 08/16] locking/lockdep: Free lock classes that are no longer in use Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 09/16] locking/lockdep: Reuse list entries " Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 10/16] locking/lockdep: Introduce lockdep_next_lockchain() and lock_chain_count() Bart Van Assche
2019-01-09 21:01 ` [PATCH v6 11/16] locking/lockdep: Reuse lock chains that have been freed Bart Van Assche
2019-01-09 21:02 ` [PATCH v6 12/16] locking/lockdep: Check data structure consistency Bart Van Assche
2019-01-09 21:02 ` [PATCH v6 13/16] locking/lockdep: Verify whether lock objects are small enough to be used as class keys Bart Van Assche
2019-01-09 21:02 ` [PATCH v6 14/16] locking/lockdep: Add support for dynamic keys Bart Van Assche
2019-01-09 21:02 ` [PATCH v6 15/16] kernel/workqueue: Use dynamic lockdep keys for workqueues Bart Van Assche
2019-01-09 21:02 ` [PATCH v6 16/16] lockdep tests: Test dynamic key registration Bart Van Assche
2019-01-11 12:48 ` [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys Peter Zijlstra
2019-01-11 15:55 ` Bart Van Assche
2019-01-11 16:55 ` Peter Zijlstra [this message]
2019-01-11 17:01 ` Bart Van Assche
2019-01-14 12:52 ` Peter Zijlstra
2019-01-14 16:52 ` Bart Van Assche
2019-01-18 9:48 ` Peter Zijlstra
2019-01-19 2:34 ` Bart Van Assche
2019-02-01 12:15 ` Peter Zijlstra
2019-02-03 17:36 ` Bart Van Assche
2019-02-08 11:43 ` Will Deacon
2019-02-08 16:31 ` Bart Van Assche
2019-02-13 22:32 ` Bart Van Assche
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