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From: David Laight <David.Laight@ACULAB.COM>
To: 'Hector Martin' <marcan@marcan.st>, Will Deacon <will@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
	Andrea Parri <parri.andrea@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Akira Yokosawa <akiyks@gmail.com>,
	"Daniel Lustig" <dlustig@nvidia.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	Jonathan Corbet <corbet@lwn.net>, Tejun Heo <tj@kernel.org>,
	"jirislaby@kernel.org" <jirislaby@kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Oliver Neukum <oneukum@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Asahi Linux <asahi@lists.linux.dev>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure
Date: Wed, 17 Aug 2022 08:20:08 +0000	[thread overview]
Message-ID: <1135281ad4e84cc5ac0147772aa83787@AcuMS.aculab.com> (raw)
In-Reply-To: <20220816070311.89186-1-marcan@marcan.st>

...
>  	p += BIT_WORD(nr);
> -	if (READ_ONCE(*p) & mask)
> -		return 1;
> -
>  	old = arch_atomic_long_fetch_or(mask, (atomic_long_t *)p);
>  	return !!(old & mask);
>  }

This looks like the same pattern (attempting to avoid a
locked bus cycle) that caused the qdisc code to sit on
transmit packets (even on x86).
That had some barriers in it (possibly nops on x86) that
didn't help - although the comments suggested otherwise.

I wonder if the pattern has been used anywhere else?

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM>
To: 'Hector Martin' <marcan@marcan.st>, Will Deacon <will@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
	Andrea Parri <parri.andrea@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Akira Yokosawa <akiyks@gmail.com>,
	"Daniel Lustig" <dlustig@nvidia.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	Jonathan Corbet <corbet@lwn.net>, Tejun Heo <tj@kernel.org>,
	"jirislaby@kernel.org" <jirislaby@kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Oliver Neukum <oneukum@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Asahi Linux <asahi@lists.linux.dev>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure
Date: Wed, 17 Aug 2022 08:20:08 +0000	[thread overview]
Message-ID: <1135281ad4e84cc5ac0147772aa83787@AcuMS.aculab.com> (raw)
In-Reply-To: <20220816070311.89186-1-marcan@marcan.st>

...
>  	p += BIT_WORD(nr);
> -	if (READ_ONCE(*p) & mask)
> -		return 1;
> -
>  	old = arch_atomic_long_fetch_or(mask, (atomic_long_t *)p);
>  	return !!(old & mask);
>  }

This looks like the same pattern (attempting to avoid a
locked bus cycle) that caused the qdisc code to sit on
transmit packets (even on x86).
That had some barriers in it (possibly nops on x86) that
didn't help - although the comments suggested otherwise.

I wonder if the pattern has been used anywhere else?

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2022-08-17  8:20 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-16  7:03 [PATCH] locking/atomic: Make test_and_*_bit() ordered on failure Hector Martin
2022-08-16  7:03 ` Hector Martin
2022-08-16  8:16 ` Arnd Bergmann
2022-08-16  8:16   ` Arnd Bergmann
2022-08-16 12:29   ` Jon Nettleton
2022-08-16 12:29     ` Jon Nettleton
2022-08-16 13:00     ` Will Deacon
2022-08-16 13:00       ` Will Deacon
2022-08-16 13:05       ` Jon Nettleton
2022-08-16 13:05         ` Jon Nettleton
2022-08-16 13:23         ` Marc Zyngier
2022-08-16 13:23           ` Marc Zyngier
2022-08-16 14:06   ` Will Deacon
2022-08-16 14:06     ` Will Deacon
2022-08-16 18:14     ` Matthew Wilcox
2022-08-16 18:14       ` Matthew Wilcox
2022-08-16 14:04 ` Will Deacon
2022-08-16 14:04   ` Will Deacon
2022-08-16 14:30   ` Hector Martin
2022-08-16 14:30     ` Hector Martin
2022-08-16 17:36     ` Will Deacon
2022-08-16 17:36       ` Will Deacon
2022-08-16 17:49       ` Jon Nettleton
2022-08-16 17:49         ` Jon Nettleton
2022-08-16 18:02         ` Linus Torvalds
2022-08-16 18:02           ` Linus Torvalds
2022-08-17  5:40           ` Jon Nettleton
2022-08-17  5:40             ` Jon Nettleton
2022-08-17  8:20 ` David Laight [this message]
2022-08-17  8:20   ` David Laight

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