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Date: Tue, 17 Jul 2018 20:36:34 -0700
From: Omar Sandoval <osandov@osandov.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Eric Biederman <ebiederm@xmission.com>,
        James Morse <james.morse@arm.com>,
        Bhupesh Sharma <bhsharma@redhat.com>, kernel-team@fb.com
Subject: Re: [PATCH v2 2/7] proc/kcore: replace kclist_lock rwlock with rwsem
Message-ID: <20180718033634.GD29351@vader>
References: <cover.1531440458.git.osandov@fb.com>
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 <20180717193841.271d1c57b6f88d75c83892be@linux-foundation.org>
 <20180718032405.GB29351@vader>
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On Tue, Jul 17, 2018 at 08:27:53PM -0700, Andrew Morton wrote:
> On Tue, 17 Jul 2018 20:24:05 -0700 Omar Sandoval <osandov@osandov.com> wrote:
> 
> > > > --- a/fs/proc/kcore.c
> > > > +++ b/fs/proc/kcore.c
> > > > @@ -59,8 +59,8 @@ struct memelfnote
> > > >  };
> > > >  
> > > >  static LIST_HEAD(kclist_head);
> > > > -static DEFINE_RWLOCK(kclist_lock);
> > > > -static int kcore_need_update = 1;
> > > > +static DECLARE_RWSEM(kclist_lock);
> > > > +static atomic_t kcore_need_update = ATOMIC_INIT(1);
> > > 
> > > It's unclear why kcore_need_update was changed to atomic_t - it's still
> > > updated under kclist_lock?
> > 
> > Not in the hotplug notifier (kcore_callback()) anymore, so I need the
> > atomic_cmpxchg() in __kcore_update_ram().
> 
> Well that's just
> 
> 	kcore_need_update = 1;
> 
> and turning that into an atomic_set doesn't change anything(?).
> 
> It's not a harmful change of course, but a bit ... odd.

The change from read, ..., write to cmpxchg in __kcore_update_ram() is
the important part, not the change from = to atomic_set(). I needed to
change that because now kcore_need_update could potentially be set again
by the hotplug notifier while we're in __kcore_update_ram(). But I'll
just put all of this in the commit message in v3 :)

> > That could use a mention in the commit message.
> 
> That never hurts ;)