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Howlett" Subject: Re: [patch 4/8] futex: Add support for unlocking robust futexes In-Reply-To: <20260318080201.GE3738010@noisy.programming.kicks-ass.net> (Peter Zijlstra's message of "Wed, 18 Mar 2026 09:02:01 +0100") References: <20260316162316.356674433@kernel.org> <20260316164951.209959583@kernel.org> <218577a9-1381-4470-a638-fa87d014da61@igalia.com> <20260317204651.GJ2872@noisy.programming.kicks-ass.net> <87wlzam65v.ffs@tglx> <20260318080201.GE3738010@noisy.programming.kicks-ass.net> Date: Wed, 18 Mar 2026 09:06:36 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 * 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