From: peterz@infradead•org (Peter Zijlstra)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 13/18] arm64: cmpxchg: avoid memory barrier on comparison failure
Date: Mon, 13 Jul 2015 17:32:26 +0200 [thread overview]
Message-ID: <20150713153226.GA19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150713145225.GG2632@arm.com>
On Mon, Jul 13, 2015 at 03:52:25PM +0100, Will Deacon wrote:
> That's an interesting case, and I think it's also broken on Alpha and Power
> (which don't use this code). It's fun actually, because a failed cmpxchg
> on those architectures gives you the barrier *before* the cmpxchg, but not
> the one afterwards so it doesn't actually help here.
>
> So there's three options afaict:
>
> (1) Document failed cmpxchg as having ACQUIRE semantics, and change this
> patch (and propose changes for Alpha and Power).
>
> -or-
>
> (2) Change pv_unhash to use fake dependency ordering across the hash.
>
> -or-
>
> (3) Put down an smp_rmb() between the cmpxchg and pv_unhash
>
> The first two sound horrible, so I'd err towards 3, particularly as this
> is x86-only code atm and I don't think it will have an effect there.
Right, I would definitely go for 3, but it does show there is code out
there :/
next prev parent reply other threads:[~2015-07-13 15:32 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-13 9:25 [PATCH 00/18] arm64: support for 8.1 LSE atomic instructions Will Deacon
2015-07-13 9:25 ` [PATCH 01/18] arm64: cpufeature.h: add missing #include of kernel.h Will Deacon
2015-07-13 9:25 ` [PATCH 02/18] arm64: atomics: move ll/sc atomics into separate header file Will Deacon
2015-07-13 9:25 ` [PATCH 03/18] arm64: elf: advertise 8.1 atomic instructions as new hwcap Will Deacon
2015-07-17 13:48 ` Catalin Marinas
2015-07-17 13:57 ` Russell King - ARM Linux
2015-07-13 9:25 ` [PATCH 04/18] arm64: alternatives: add cpu feature for lse atomics Will Deacon
2015-07-13 9:25 ` [PATCH 05/18] arm64: introduce CONFIG_ARM64_LSE_ATOMICS as fallback to ll/sc atomics Will Deacon
2015-07-17 16:32 ` Catalin Marinas
2015-07-17 17:25 ` Will Deacon
2015-07-13 9:25 ` [PATCH 06/18] arm64: atomics: patch in lse instructions when supported by the CPU Will Deacon
2015-07-13 9:25 ` [PATCH 07/18] arm64: locks: " Will Deacon
2015-07-21 16:53 ` Catalin Marinas
2015-07-21 17:29 ` Will Deacon
2015-07-23 13:39 ` Will Deacon
2015-07-23 14:14 ` Catalin Marinas
2015-07-13 9:25 ` [PATCH 08/18] arm64: bitops: " Will Deacon
2015-07-13 9:25 ` [PATCH 09/18] arm64: xchg: " Will Deacon
2015-07-13 9:25 ` [PATCH 10/18] arm64: cmpxchg: " Will Deacon
2015-07-13 9:25 ` [PATCH 11/18] arm64: cmpxchg_dbl: " Will Deacon
2015-07-13 9:25 ` [PATCH 12/18] arm64: cmpxchg: avoid "cc" clobber in ll/sc routines Will Deacon
2015-07-21 17:16 ` Catalin Marinas
2015-07-21 17:32 ` Will Deacon
2015-07-13 9:25 ` [PATCH 13/18] arm64: cmpxchg: avoid memory barrier on comparison failure Will Deacon
2015-07-13 10:28 ` Peter Zijlstra
2015-07-13 11:22 ` Will Deacon
2015-07-13 13:39 ` Peter Zijlstra
2015-07-13 14:52 ` Will Deacon
2015-07-13 15:32 ` Peter Zijlstra [this message]
2015-07-13 15:58 ` Will Deacon
2015-07-13 9:25 ` [PATCH 14/18] arm64: atomics: tidy up common atomic{,64}_* macros Will Deacon
2015-07-13 9:25 ` [PATCH 15/18] arm64: atomics: prefetch the destination word for write prior to stxr Will Deacon
2015-07-13 9:25 ` [PATCH 16/18] arm64: atomics: implement atomic{, 64}_cmpxchg using cmpxchg Will Deacon
2015-07-13 9:25 ` [PATCH 17/18] arm64: atomic64_dec_if_positive: fix incorrect branch condition Will Deacon
2015-07-13 9:25 ` [PATCH 18/18] arm64: kconfig: select HAVE_CMPXCHG_LOCAL Will Deacon
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