linux-kernel - Re: [PATCH 1/7] atomics/tty: add missing atomic_long

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Date:   Fri, 22 Jun 2018 17:55:59 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Hurley <peter@...leysoftware.com>
Subject: Re: [PATCH 1/7] atomics/tty: add missing atomic_long_t * cast

Hi,

On Wed, Jun 06, 2018 at 04:00:42PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jun 05, 2018 at 04:53:34PM +0200, Peter Zijlstra wrote:
> > On Tue, Jun 05, 2018 at 04:43:04PM +0200, Peter Zijlstra wrote:
> > 
> > > I can make a proper patch, hold on.
> > 
> > ---
> > Subject: atomic/tty: Fix up atomic abuse in ldsem
> > 
> > Mark found ldsem_cmpxchg() needed an (atomic_long_t *) cast to keep
> > working after making the atomic_long interface type safe.
> > 
> > Needing casts is bad form, which made me look at the code. There are no
> > ld_semaphore::count users outside of these functions so there is no
> > reason why it can not be an atomic_long_t in the first place, obviating
> > the need for this cast.
> > 
> > That also ensures the loads use atomic_long_read(), which implies (at
> > least) READ_ONCE() in order to guarantee single-copy-atomic loads.
> > 
> > When using atomic_long_try_cmpxchg() the ldsem_cmpxchg() wrapper gets
> > very thin (the only difference is not changing *old on success, which
> > most callers don't seem to care about).
> > 
> > So rework the whole thing to use atomic_long_t and its accessors
> > directly.
> > 
> > While there, fixup all the horrible comment styles.
> > 
> > Cc: Peter Hurley <peter@...leysoftware.com>
> > Reported-by: Mark Rutland <mark.rutland@....com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> Looks good, I'll queue this up after 4.18-rc1 is out, thanks.

Now that v4.18-rc1 is out, I thought I'd ping so that this doesn't get
forgotten.

Have a good weekend!

Mark.