From: Peter Zijlstra <peterz@infradead.org>
To: stern@rowland.harvard.edu, akiyks@gmail.com,
andrea.parri@amarulasolutions.com, boqun.feng@gmail.com,
dlustig@nvidia.com, dhowells@redhat.com, j.alglave@ucl.ac.uk,
luc.maranget@inria.fr, npiggin@gmail.com, paulmck@linux.ibm.com,
will.deacon@arm.com
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
Huacai Chen <chenhc@lemote.com>, Huang Pei <huangpei@loongson.cn>,
Paul Burton <paul.burton@mips.com>
Subject: Re: [RFC][PATCH 2/5] mips/atomic: Fix loongson_llsc_mb() wreckage
Date: Wed, 24 Apr 2019 14:59:13 +0200 [thread overview]
Message-ID: <20190424125913.GO12232@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190424124421.636767843@infradead.org>
On Wed, Apr 24, 2019 at 02:36:58PM +0200, Peter Zijlstra wrote:
> The comment describing the loongson_llsc_mb() reorder case doesn't
> make any sense what so ever. Instruction re-ordering is not an SMP
> artifact, but rather a CPU local phenomenon. This means that _every_
> LL/SC loop needs this barrier right in front to avoid the CPU from
> leaking a memop inside it.
>
> For the branch speculation case; if futex_atomic_cmpxchg_inatomic()
> needs one at the bne branch target, then surely the normal
> __cmpxch_asmg() implementation does too. We cannot rely on the
> barriers from cmpxchg() because cmpxchg_local() is implemented with
> the same macro, and branch prediction and speculation are, too, CPU
> local.
Also; just doing them all makes for much simpler rules and less
mistakes.
next prev parent reply other threads:[~2019-04-24 12:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-24 12:36 [RFC][PATCH 0/5] atomic: Fixes to smp_mb__{before,after}_atomic() and mips Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 1/5] mips/atomic: Fix cmpxchg64 barriers Peter Zijlstra
2019-04-24 21:00 ` Paul Burton
2019-04-25 6:59 ` Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 2/5] mips/atomic: Fix loongson_llsc_mb() wreckage Peter Zijlstra
2019-04-24 12:59 ` Peter Zijlstra [this message]
2019-04-24 21:18 ` Paul Burton
2019-04-25 4:58 ` huangpei
2019-04-25 7:33 ` Peter Zijlstra
2019-04-25 9:09 ` Peter Zijlstra
2019-04-25 12:14 ` huangpei
2019-04-25 9:12 ` Peter Zijlstra
2019-05-14 15:58 ` Peter Zijlstra
2019-05-14 16:10 ` Linus Torvalds
2019-05-14 16:56 ` Peter Zijlstra
2019-05-14 17:07 ` Linus Torvalds
2019-05-15 13:50 ` huangpei
2019-04-25 11:32 ` huangpei
2019-04-25 12:26 ` Peter Zijlstra
2019-04-25 12:51 ` huangpei
2019-04-25 13:31 ` Peter Zijlstra
2019-04-26 2:57 ` huangpei
2019-05-14 15:46 ` Peter Zijlstra
2019-04-25 16:12 ` Linus Torvalds
2019-04-25 7:15 ` Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 3/5] mips/atomic: Optimize loongson3_llsc_mb() Peter Zijlstra
2019-04-24 12:37 ` [RFC][PATCH 4/5] mips/atomic: Fix smp_mb__{before,after}_atomic() Peter Zijlstra
2019-04-24 21:24 ` Paul Burton
2019-04-25 7:34 ` Peter Zijlstra
2019-04-24 12:37 ` [RFC][PATCH 5/5] x86/atomic: " Peter Zijlstra
2019-04-24 13:41 ` Will Deacon
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