linux-kernel - Re: [RFC][PATCH 03/31] locking,arc: Implement atomic_fetch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <C2D7FE5348E1B147BCA15975FBA23075F4E9F138@us01wembx1.internal.synopsys.com>
Date:	Mon, 25 Apr 2016 04:26:54 +0000
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"will.deacon@....com" <will.deacon@....com>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>,
	"waiman.long@....com" <waiman.long@....com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"egtvedt@...fundet.no" <egtvedt@...fundet.no>,
	"realmz6@...il.com" <realmz6@...il.com>,
	"ysato@...rs.sourceforge.jp" <ysato@...rs.sourceforge.jp>,
	"rkuo@...eaurora.org" <rkuo@...eaurora.org>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"geert@...ux-m68k.org" <geert@...ux-m68k.org>,
	"james.hogan@...tec.com" <james.hogan@...tec.com>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"jejb@...isc-linux.org" <jejb@...isc-linux.org>,
	"mpe@...erman.id.au" <mpe@...erman.id.au>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"dalias@...c.org" <dalias@...c.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"cmetcalf@...lanox.com" <cmetcalf@...lanox.com>,
	"jcmvbkbc@...il.com" <jcmvbkbc@...il.com>,
	"arnd@...db.de" <arnd@...db.de>, "dbueso@...e.de" <dbueso@...e.de>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>
Subject: Re: [RFC][PATCH 03/31] locking,arc: Implement
 atomic_fetch_{add,sub,and,andnot,or,xor}()

On Friday 22 April 2016 07:46 PM, Peter Zijlstra wrote:
> On Fri, Apr 22, 2016 at 10:50:41AM +0000, Vineet Gupta wrote:
>
>>> > > +#define ATOMIC_FETCH_OP(op, c_op, asm_op)				\
>>> > > +static inline int atomic_fetch_##op(int i, atomic_t *v)			\
>>> > > +{									\
>>> > > +	unsigned int val, result;			                \
>>> > > +	SCOND_FAIL_RETRY_VAR_DEF                                        \
>>> > > +									\
>>> > > +	/*								\
>>> > > +	 * Explicit full memory barrier needed before/after as		\
>>> > > +	 * LLOCK/SCOND thmeselves don't provide any such semantics	\
>>> > > +	 */								\
>>> > > +	smp_mb();							\
>>> > > +									\
>>> > > +	__asm__ __volatile__(						\
>>> > > +	"1:	llock   %[val], [%[ctr]]		\n"		\
>>> > > +	"	mov %[result], %[val]			\n"		\
>> > 
>> > Calling it result could be a bit confusing, this is meant to be the "orig" value.
>> > So it indeed "result" of the API, but for atomic operation it is pristine value.
>> > 
>> > Also we can optimize away that MOV - given there are plenty of regs, so
>> > 
>>> > > +	"	" #asm_op " %[val], %[val], %[i]	\n"		\
>>> > > +	"	scond   %[val], [%[ctr]]		\n"		\
>> > 
>> > Instead have
>> > 
>> > +	"	" #asm_op " %[result], %[val], %[i]	\n"		\
>> > +	"	scond   %[result], [%[ctr]]		\n"		\
>> > 
>> > 
> Indeed, how about something like so?
>
> ---
> Subject: locking,arc: Implement atomic_fetch_{add,sub,and,andnot,or,xor}()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Apr 18 01:16:09 CEST 2016
>
> Implement FETCH-OP atomic primitives, these are very similar to the
> existing OP-RETURN primitives we already have, except they return the
> value of the atomic variable _before_ modification.
>
> This is especially useful for irreversible operations -- such as
> bitops (because it becomes impossible to reconstruct the state prior
> to modification).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Vineet Gupta <vgupta@...opsys.com>