From: peterz@infradead.org (Peter Zijlstra)
To: linux-riscv@lists.infradead.org
Subject: [RFC PATCH] riscv/locking: Strengthen spin_lock() and spin_unlock()
Date: Tue, 6 Mar 2018 14:00:59 +0100 [thread overview]
Message-ID: <20180306130059.GE25201@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFyT=+8m0mmpeegP8LOVtkCYv3O2vyO-ZcQdLAR=s309jg@mail.gmail.com>
On Mon, Feb 26, 2018 at 09:00:43AM -0800, Linus Torvalds wrote:
> On Mon, Feb 26, 2018 at 8:24 AM, Will Deacon <will.deacon@arm.com> wrote:
> >
> > Strictly speaking, that's not what we've got implemented on arm64: only
> > the read part of the RmW has Acquire semantics, but there is a total
> > order on the lock/unlock operations for the lock.
>
> Hmm.
>
> I thought we had exactly that bug on some architecture with the queued
> spinlocks, and people decided it was wrong.
So ARM64 and Power have the acquire-on-load only thing, but qspinlock
has it per construction on anything that allowes reordering stores.
Given that unlock/lock are ordered, which covers about 99% of the users
out there, and fixing the issue would make things significantly slower
on the weak architectures we let it be.
But yes, its a pesky detail.
next prev parent reply other threads:[~2018-03-06 13:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 12:19 [RFC PATCH] riscv/locking: Strengthen spin_lock() and spin_unlock() Andrea Parri
2018-02-22 12:44 ` Andrea Parri
2018-02-22 13:40 ` Peter Zijlstra
2018-02-22 14:12 ` Andrea Parri
2018-02-22 17:27 ` Daniel Lustig
2018-02-22 18:13 ` Paul E. McKenney
2018-02-22 18:27 ` Peter Zijlstra
2018-02-22 19:47 ` Daniel Lustig
2018-02-23 11:16 ` Andrea Parri
2018-02-26 10:39 ` Will Deacon
2018-02-26 14:21 ` Luc Maranget
2018-02-26 16:06 ` Linus Torvalds
2018-02-26 16:24 ` Will Deacon
2018-02-26 17:00 ` Linus Torvalds
2018-02-26 17:10 ` Will Deacon
2018-03-06 13:00 ` Peter Zijlstra [this message]
2018-02-27 5:06 ` Boqun Feng
2018-02-27 10:16 ` Boqun Feng
2018-03-01 15:11 ` Andrea Parri
2018-03-01 21:54 ` Palmer Dabbelt
2018-03-01 22:21 ` Daniel Lustig
2018-02-22 20:02 ` Paul E. McKenney
2018-02-22 18:21 ` 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=20180306130059.GE25201@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=linux-riscv@lists.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