From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH v7 1/7] Restartable sequences system call
Date: Wed, 10 Aug 2016 09:50:44 +0200
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Russell King <linux@arm.linux.org.uk>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, linux-kernel <linux-kernel@vger.kernel.org>, linux-api <linux-api@vger.kernel.org>, Paul Turner <pjt@google.com>, Andrew Hunter <ahh@google.com>, Andy Lutomirski <luto@amacapital.net>, Andi Kleen <andi@firstfloor.org>, Dave Watson <davejwatson@fb.com>, Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>, rostedt <rostedt@goodmis.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Josh Triplett <josh@joshtriplett.org>, Linus Torvalds <torvalds@linux-foundation.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Michael Kerrisk <mtk.manpages@gmail.com>, Boqun Feng <boqun.feng@gmail.com>
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On Tue, Aug 09, 2016 at 10:41:47PM +0000, Mathieu Desnoyers wrote:
> #ifdef __LP64__
> 
> static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
> {
>         union rseq_cpu_event u;
> 
>         u.e.cpu_id = raw_smp_processor_id();
>         u.e.event_counter = ++t->rseq_event_counter;
>         if (__put_user(u.v, &t->rseq->u.v))
>                 return false;
>         trace_rseq_inc(t->rseq_event_counter);
>         return true;
> }
> 
> #else /* #ifdef __LP64__ */
> 
> static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
> {
>         if (__put_user(raw_smp_processor_id(), &t->rseq->u.e.cpu_id))
>                 return false;
>         if (__put_user(++t->rseq_event_counter, &t->rseq->u.e.event_counter))
>                 return false;
>         trace_rseq_inc(t->rseq_event_counter);
>         return true;
> }
> 
> #endif /* #else #ifdef __LP64__ */

I don't think you need to guard it (and CONFIG_64BIT is the 'right'
kernel symbol for that), 32bit should have u64 __put_user() only
implemented as 2 u32 stores.