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

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Date:   Wed, 6 Jun 2018 16:00:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>, 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

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.

greg k-h