linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Will Deacon <will.deacon@arm.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com,
	Ingo Molnar <mingo@elte.hu>, Boqun Feng <boqun.feng@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	1vier1@web.de, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH 1/4] spinlock: Document memory barrier rules
Date: Thu, 1 Sep 2016 12:19:15 +0100	[thread overview]
Message-ID: <20160901111915.GB6721@arm.com> (raw)
In-Reply-To: <3f7c39e5-4c46-0641-d29e-36c9439ad6dc@colorfullife.com>

On Thu, Sep 01, 2016 at 01:04:26PM +0200, Manfred Spraul wrote:
> If I understand it right, the rules are:
> 1. spin_unlock_wait() must behave like spin_lock();spin_unlock();
> 2. spin_is_locked() must behave like spin_trylock() ? spin_unlock(),TRUE :
> FALSE

I don't think spin_is_locked is as strong as all that. On arm64 and ppc,
it's just smp_mb(); followed by a check on the lock value. It can't be
used for the same sorts of inter-CPU synchronisation that spin_unlock_wait
provides.

> 3. the ACQUIRE during spin_lock applies to the lock load, not to the store.

Correct. This is already documented for things like cmpxchg.

> sem.c and nf_conntrack.c need only rule 1 now, but I would document the rest
> as well, ok?
> 
> I'll update the patches.

Please CC me!

Will

  reply	other threads:[~2016-09-01 11:19 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-28 11:56 [PATCH 0/4] Clarify/standardize memory barriers for lock/unlock Manfred Spraul
2016-08-28 11:56 ` [PATCH 1/4] spinlock: Document memory barrier rules Manfred Spraul
2016-08-28 11:56   ` [PATCH 2/4] barrier.h: Move smp_mb__after_unlock_lock to barrier.h Manfred Spraul
2016-08-28 11:56     ` [PATCH 3/4] net/netfilter/nf_conntrack_core: update memory barriers Manfred Spraul
2016-08-28 11:56       ` [PATCH 4/4] qspinlock for x86: smp_mb__after_spin_lock() is free Manfred Spraul
2016-08-29 10:52         ` Peter Zijlstra
2016-08-29 10:51       ` [PATCH 3/4] net/netfilter/nf_conntrack_core: update memory barriers Peter Zijlstra
2016-08-28 13:43     ` [PATCH 2/4] barrier.h: Move smp_mb__after_unlock_lock to barrier.h Paul E. McKenney
2016-08-28 16:31       ` Manfred Spraul
2016-08-28 18:00       ` Manfred Spraul
2016-08-28 14:41     ` kbuild test robot
2016-08-28 17:43       ` [PATCH 2/4 v3] spinlock.h: Move smp_mb__after_unlock_lock to spinlock.h Manfred Spraul
2016-08-29 10:48   ` [PATCH 1/4] spinlock: Document memory barrier rules Peter Zijlstra
2016-08-29 12:54     ` Manfred Spraul
2016-08-29 13:44       ` Peter Zijlstra
2016-08-31  4:59         ` Manfred Spraul
2016-08-31 15:40           ` Peter Zijlstra
2016-08-31 16:40             ` Will Deacon
2016-08-31 18:32               ` Manfred Spraul
2016-09-01  8:44                 ` Peter Zijlstra
2016-09-01 11:04                   ` Manfred Spraul
2016-09-01 11:19                     ` Will Deacon [this message]
2016-09-01 11:51                     ` Peter Zijlstra
2016-09-01 14:05                       ` Boqun Feng
2016-08-29 10:53 ` [PATCH 0/4] Clarify/standardize memory barriers for lock/unlock Peter Zijlstra

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20160901111915.GB6721@arm.com \
    --to=will.deacon@arm.com \
    --cc=1vier1@web.de \
    --cc=akpm@linux-foundation.org \
    --cc=benh@kernel.crashing.org \
    --cc=boqun.feng@gmail.com \
    --cc=dave@stgolabs.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=manfred@colorfullife.com \
    --cc=mingo@elte.hu \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).