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From: Florian Weimer <fweimer@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Thomas Gleixner" <tglx@kernel.org>,
	"André Almeida" <andrealmeid@igalia.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	"Carlos O'Donell" <carlos@redhat.com>,
	"Rich Felker" <dalias@aerifal.cx>,
	"Torvald Riegel" <triegel@redhat.com>,
	"Darren Hart" <dvhart@infradead.org>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Liam R . Howlett" <Liam.Howlett@oracle.com>
Subject: Re: [patch 4/8] futex: Add support for unlocking robust futexes
Date: Wed, 18 Mar 2026 09:06:36 +0100	[thread overview]
Message-ID: <lhubjglzhmb.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20260318080201.GE3738010@noisy.programming.kicks-ass.net> (Peter Zijlstra's message of "Wed, 18 Mar 2026 09:02:01 +0100")

* Peter Zijlstra:

>> No. There is a syscall in between and if that is not sufficient then the
>> architecure has more severe troubles than that store, no?
>
> So I think we once tried to determine if syscall could be considered to
> imply memory ordering, and I think the take-away at the time was that we
> could not assume so.
>
> But its been a long time, maybe I misremember.

I remember the same thing, and I think I saw test failures where system
calls where not a (strong) barrier on POWER.

However, some system calls better be barriers.  For example, writing to
a pipe should synchronize with reading from the pipe and poll wakeup on
the read end.  Likewise for sockets, I assume.  As far as I know, POSIX
is silent on this topic, though.

Thanks,
Florian


  reply	other threads:[~2026-03-18  8:06 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-16 17:12 [patch 0/8] futex: Address the robust futex unlock race for real Thomas Gleixner
2026-03-16 17:12 ` [patch 1/8] futex: Move futex task related data into a struct Thomas Gleixner
2026-03-16 17:55   ` Mathieu Desnoyers
2026-03-17  2:24   ` André Almeida
2026-03-17  9:52     ` Thomas Gleixner
2026-03-16 17:13 ` [patch 2/8] futex: Move futex related mm_struct " Thomas Gleixner
2026-03-16 18:00   ` Mathieu Desnoyers
2026-03-16 17:13 ` [patch 3/8] futex: Provide UABI defines for robust list entry modifiers Thomas Gleixner
2026-03-16 18:02   ` Mathieu Desnoyers
2026-03-17  2:38   ` André Almeida
2026-03-17  9:53     ` Thomas Gleixner
2026-03-16 17:13 ` [patch 4/8] futex: Add support for unlocking robust futexes Thomas Gleixner
2026-03-16 18:24   ` Mathieu Desnoyers
2026-03-17 16:17   ` André Almeida
2026-03-17 20:46     ` Peter Zijlstra
2026-03-17 22:40       ` Thomas Gleixner
2026-03-18  8:02         ` Peter Zijlstra
2026-03-18  8:06           ` Florian Weimer [this message]
2026-03-18 14:47           ` Peter Zijlstra
2026-03-18 16:03             ` Thomas Gleixner
2026-03-16 17:13 ` [patch 5/8] futex: Add robust futex unlock IP range Thomas Gleixner
2026-03-16 18:36   ` Mathieu Desnoyers
2026-03-17 19:19   ` André Almeida
2026-03-16 17:13 ` [patch 6/8] futex: Provide infrastructure to plug the non contended robust futex unlock race Thomas Gleixner
2026-03-16 18:35   ` Mathieu Desnoyers
2026-03-16 20:29     ` Thomas Gleixner
2026-03-16 20:52       ` Mathieu Desnoyers
2026-03-16 17:13 ` [patch 7/8] x86/vdso: Prepare for robust futex unlock support Thomas Gleixner
2026-03-16 17:13 ` [patch 8/8] x86/vdso: Implement __vdso_futex_robust_try_unlock() Thomas Gleixner
2026-03-16 19:19   ` Mathieu Desnoyers
2026-03-16 21:02     ` Thomas Gleixner
2026-03-16 22:35       ` Mathieu Desnoyers
2026-03-16 21:14     ` Thomas Gleixner
2026-03-16 21:29     ` Thomas Gleixner
2026-03-17  7:25   ` Thomas Weißschuh
2026-03-17  9:51     ` Thomas Gleixner
2026-03-17 11:17       ` Thomas Weißschuh
2026-03-18 16:17         ` Thomas Gleixner
2026-03-19  7:41           ` Thomas Weißschuh
2026-03-19  8:53             ` Florian Weimer
2026-03-19  9:04               ` Thomas Weißschuh
2026-03-19  9:08               ` Peter Zijlstra
2026-03-19 23:31                 ` Thomas Gleixner
2026-03-19 10:36             ` Sebastian Andrzej Siewior
2026-03-19 10:49               ` Thomas Weißschuh
2026-03-19 10:55                 ` Sebastian Andrzej Siewior
2026-03-17  8:28   ` Florian Weimer
2026-03-17  9:36     ` Thomas Gleixner
2026-03-17 10:37       ` Florian Weimer
2026-03-17 22:32         ` Thomas Gleixner
2026-03-18 22:08           ` Thomas Gleixner
2026-03-18 22:10             ` Peter Zijlstra
2026-03-19  2:05             ` André Almeida
2026-03-19  7:10               ` Thomas Gleixner
2026-03-17 15:33   ` Uros Bizjak
2026-03-18  8:21     ` Thomas Gleixner
2026-03-18  8:32       ` Uros Bizjak

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