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Date:   Fri, 24 May 2019 13:38:22 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Andrea Parri <andrea.parri@amarulasolutions.com>,
        linux-kernel@vger.kernel.org, will.deacon@arm.com,
        aou@eecs.berkeley.edu, arnd@arndb.de, bp@alien8.de,
        catalin.marinas@arm.com, davem@davemloft.net, fenghua.yu@intel.com,
        heiko.carstens@de.ibm.com, herbert@gondor.apana.org.au,
        ink@jurassic.park.msu.ru, jhogan@kernel.org, linux@armlinux.org.uk,
        mattst88@gmail.com, mingo@kernel.org, mpe@ellerman.id.au,
        palmer@sifive.com, paul.burton@mips.com, paulus@samba.org,
        ralf@linux-mips.org, rth@twiddle.net, stable@vger.kernel.org,
        tglx@linutronix.de, tony.luck@intel.com, vgupta@synopsys.com,
        jhansen@vmware.com, vdasa@vmware.com, aditr@vmware.com,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup
Message-ID: <20190524113822.GA32272@kroah.com>
References: <20190522132250.26499-1-mark.rutland@arm.com>
 <20190523083013.GA4616@andrea>
 <20190523101926.GA3370@lakrids.cambridge.arm.com>
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 <20190524111807.GS2650@hirez.programming.kicks-ass.net>
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On Fri, May 24, 2019 at 01:18:07PM +0200, Peter Zijlstra wrote:
> On Fri, May 24, 2019 at 12:37:31PM +0200, Peter Zijlstra wrote:
> > On Thu, May 23, 2019 at 11:19:26AM +0100, Mark Rutland wrote:
> > 
> > > [mark@lakrids:~/src/linux]% git grep '\(return\|=\)\s\+atomic\(64\)\?_set'
> > > include/linux/vmw_vmci_defs.h:  return atomic_set((atomic_t *)var, (u32)new_val);
> > > include/linux/vmw_vmci_defs.h:  return atomic64_set(var, new_val);
> > > 
> > 
> > Oh boy, what a load of crap you just did find.
> > 
> > How about something like the below? I've not read how that buffer is
> > used, but the below preserves all broken without using atomic*_t.
> 
> Clarified by something along these lines?
> 
> ---
>  Documentation/atomic_t.txt | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> index dca3fb0554db..125c95ddbbc0 100644
> --- a/Documentation/atomic_t.txt
> +++ b/Documentation/atomic_t.txt
> @@ -83,6 +83,9 @@ The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
>  implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
>  smp_store_release() respectively.
>  
> +Therefore, if you find yourself only using the Non-RMW operations of atomic_t,
> +you do not in fact need atomic_t at all and are doing it wrong.
> +
>  The one detail to this is that atomic_set{}() should be observable to the RMW
>  ops. That is:
>  

I like it!

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>