From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Thomas Gleixner <tglx@linutronix.de>,
Joel Fernandes <joel@joelfernandes.org>,
Alan Stern <stern@rowland.harvard.edu>,
rostedt <rostedt@goodmis.org>,
Valentin Schneider <valentin.schneider@arm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates
Date: Wed, 21 Aug 2019 17:33:25 +0200 [thread overview]
Message-ID: <20190821153325.GD2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190821132310.GC28441@linux.ibm.com>
On Wed, Aug 21, 2019 at 06:23:10AM -0700, Paul E. McKenney wrote:
> On Wed, Aug 21, 2019 at 11:32:01AM +0100, Will Deacon wrote:
> > and so it is using a store-pair instruction to reduce the complexity in
> > the immediate generation. Thus, the 64-bit store will only have 32-bit
> > atomicity. In fact, this is scary because if I change bar to:
> >
> > void bar(u64 *x)
> > {
> > *(volatile u64 *)x = 0xabcdef10abcdef10;
> > }
> >
> > then I get:
> >
> > bar:
> > mov w1, 61200
> > movk w1, 0xabcd, lsl 16
> > str w1, [x0]
> > str w1, [x0, 4]
> > ret
> >
> > so I'm not sure that WRITE_ONCE would even help :/
>
> Well, I can have the LWN article cite your email, then. So thank you
> very much!
>
> Is generation of this code for a 64-bit volatile store considered a bug?
> Or does ARMv8 exclude the possibility of 64-bit MMIO registers? And I
> would guess that Thomas and Linus would ask a similar bugginess question
> for normal stores. ;-)
I'm calling this a compiler bug; the way I understand volatile this is
very much against the intentended use case. That is, this is buggy even
on UP vs signals or MMIO.
next prev parent reply other threads:[~2019-08-21 15:34 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 10:29 WARNING in tracepoint_probe_register_prio (3) syzbot
2019-08-16 0:11 ` syzbot
2019-08-16 14:26 ` [PATCH 1/1] Fix: trace sched switch start/stop racy updates Mathieu Desnoyers
2019-08-16 16:25 ` Steven Rostedt
2019-08-16 16:48 ` Valentin Schneider
2019-08-16 17:04 ` Steven Rostedt
2019-08-16 17:41 ` Mathieu Desnoyers
2019-08-16 19:18 ` Steven Rostedt
2019-08-16 19:19 ` Alan Stern
2019-08-16 20:44 ` Joel Fernandes
2019-08-16 20:49 ` Thomas Gleixner
2019-08-16 20:57 ` Joel Fernandes
2019-08-16 22:27 ` Valentin Schneider
2019-08-16 22:57 ` Linus Torvalds
2019-08-17 1:41 ` Mathieu Desnoyers
2019-08-17 4:52 ` Paul E. McKenney
2019-08-17 8:28 ` Linus Torvalds
2019-08-17 8:44 ` Linus Torvalds
2019-08-17 15:02 ` Mathieu Desnoyers
2019-08-17 20:03 ` Valentin Schneider
2019-08-17 23:00 ` Paul E. McKenney
2019-08-19 10:34 ` Valentin Schneider
2019-08-17 22:28 ` Paul E. McKenney
2019-08-20 14:01 ` Peter Zijlstra
2019-08-20 20:31 ` Paul E. McKenney
2019-08-20 20:39 ` Peter Zijlstra
2019-08-20 20:52 ` Paul E. McKenney
2019-08-16 21:04 ` Linus Torvalds
2019-08-17 1:36 ` Mathieu Desnoyers
2019-08-17 2:13 ` Steven Rostedt
2019-08-17 14:40 ` Mathieu Desnoyers
2019-08-17 15:26 ` Steven Rostedt
2019-08-17 15:55 ` Mathieu Desnoyers
2019-08-17 16:40 ` Steven Rostedt
2019-08-17 22:06 ` Paul E. McKenney
2019-08-17 8:08 ` Linus Torvalds
2019-08-20 13:56 ` Peter Zijlstra
2019-08-20 20:29 ` Paul E. McKenney
2019-08-21 10:32 ` Will Deacon
2019-08-21 13:23 ` Paul E. McKenney
2019-08-21 13:32 ` Will Deacon
2019-08-21 13:56 ` Paul E. McKenney
2019-08-21 16:22 ` Will Deacon
2019-08-21 15:33 ` Peter Zijlstra [this message]
2019-08-21 15:48 ` Mathieu Desnoyers
2019-08-21 16:14 ` Paul E. McKenney
2019-08-21 19:03 ` Joel Fernandes
2019-09-09 6:21 ` Herbert Xu
2019-08-16 20:49 ` Steven Rostedt
2019-08-16 20:59 ` Joel Fernandes
2019-08-17 1:25 ` Mathieu Desnoyers
2019-08-18 9:15 ` stable markup was " Pavel Machek
2019-08-16 17:19 ` Mathieu Desnoyers
2019-08-16 19:15 ` Steven Rostedt
2019-08-17 14:27 ` Mathieu Desnoyers
2019-08-17 15:42 ` Steven Rostedt
2019-08-17 15:53 ` Mathieu Desnoyers
2019-08-17 16:43 ` Steven Rostedt
2019-08-16 12:32 ` WARNING in tracepoint_probe_register_prio (3) syzbot
2019-08-16 12:41 ` Sebastian Andrzej Siewior
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=20190821153325.GD2349@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=boqun.feng@gmail.com \
--cc=dhowells@redhat.com \
--cc=joel@joelfernandes.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@linux.ibm.com \
--cc=rostedt@goodmis.org \
--cc=stern@rowland.harvard.edu \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=valentin.schneider@arm.com \
--cc=will.deacon@arm.com \
--cc=will@kernel.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).