From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: sashiko-reviews@lists.linux.dev
Cc: linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] locking/ww_mutex/test: Time an ABBA with both owners running
Date: Fri, 6 Nov 2026 19:27:35 -0500 [thread overview]
Message-ID: <81e4b915-0c18-49fc-b015-b543b26d1a8e@efficios.com> (raw)
In-Reply-To: <sashiko-outbox-202413@kernel.org>
On 2026-11-06 19:11, sashiko-bot@kernel.org wrote:
> Can abba_spin_young() obtain a smaller ctx.stamp than abba_spin_old() on
> weakly-ordered architectures?
[...]
> Using atomic_set_release() and atomic_read_acquire() on s->stage would
> order the stamp allocations.
Right. ww_acquire_init() takes the stamp with a relaxed increment, and
nothing orders it before the relaxed store of stage 1: on a
weakly-ordered CPU the younger thread can take the older stamp, wound
the other one, and the test fails with -EDEADLK where nothing is wrong.
x86 does not reorder them. v2 makes each stage store a release and the
poll an acquire.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
prev parent reply other threads:[~2026-11-07 0:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-06 23:59 [PATCH 0/5] locking/rtmutex: priority inheritance fixes and tests Mathieu Desnoyers
2026-11-06 23:59 ` [PATCH 1/5] locking/rtmutex: Stop spinning on the owner when the waiter is woken Mathieu Desnoyers
2026-11-06 23:59 ` [PATCH 2/5] locking/rtmutex: Initialize the ww_mutex context of a waiter Mathieu Desnoyers
2026-11-06 23:59 ` [PATCH 3/5] locking/rtmutex: Clone a waiter's sort keys as it enters pi_waiters Mathieu Desnoyers
2026-11-06 23:59 ` [PATCH 4/5] selftests/futex: Test priority inheritance on PI futexes Mathieu Desnoyers
2026-11-06 23:59 ` [PATCH 5/5] locking/ww_mutex/test: Time an ABBA with both owners running Mathieu Desnoyers
2026-11-07 0:11 ` sashiko-bot
2026-11-07 0:27 ` Mathieu Desnoyers [this message]
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