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Date: Wed, 3 Jun 2026 10:42:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	=?iso-8859-1?Q?Andr=E9?= Almeida <andrealmeid@igalia.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Carlos O'Donell <carlos@redhat.com>,
	Florian Weimer <fweimer@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>,
	Uros Bizjak <ubizjak@gmail.com>,
	Thomas =?iso-8859-1?Q?Wei=DFschuh?= <linux@weissschuh.net>,
	Mark Brown <broonie@kernel.org>,
	Richard Weinberger <richard@nod.at>
Subject: Re: [patch V5 11/16] futex: Provide infrastructure to plug the non
 contended robust futex unlock race
Message-ID: <20260603084240.GT3102624@noisy.programming.kicks-ass.net>
References: <20260602084648.462672743@kernel.org>
 <20260602090535.773669210@kernel.org>
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In-Reply-To: <20260602090535.773669210@kernel.org>

On Tue, Jun 02, 2026 at 11:10:04AM +0200, Thomas Gleixner wrote:
> When the FUTEX_ROBUST_UNLOCK mechanism is used for unlocking (PI-)futexes,
> then the unlock sequence in user space looks like this:
> 
>   1)	robust_list_set_op_pending(mutex);
>   2)	robust_list_remove(mutex);
> 	
>   	lval = gettid();
>   3)	if (atomic_try_cmpxchg(&mutex->lock, lval, 0))
>   4)		robust_list_clear_op_pending();
>   	else
>   5)		sys_futex(OP | FUTEX_ROBUST_UNLOCK, ....);

Ah!, see, your uapi patch earlier called that FUTEX_UNLOCK_ROBUST.

I'll fix it all up if I don't fine real issues.