linux-kernel - Re: [PATCH v2 2/7] proc/kcore: replace kclist

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Message-ID: <20180718032405.GB29351@vader>
Date:   Tue, 17 Jul 2018 20:24:05 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        James Morse <james.morse@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>, kernel-team@...com
Subject: Re: [PATCH v2 2/7] proc/kcore: replace kclist_lock rwlock with rwsem

On Tue, Jul 17, 2018 at 07:38:41PM -0700, Andrew Morton wrote:
> On Thu, 12 Jul 2018 17:09:34 -0700 Omar Sandoval <osandov@...ndov.com> wrote:
> 
> > From: Omar Sandoval <osandov@...com>
> > 
> > Now we only need kclist_lock from user context and at fs init time, and
> > the following changes need to sleep while holding the kclist_lock.
> > 
> > ...
> >
> > --- 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(). That could use a mention in
the commit message.

> Maybe it's for a later patch.
> 
>