From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [RFC PATCH v11 for 4.15 01/24] Restartable sequences system call
Date: Thu, 16 Nov 2017 19:43:05 +0100
Message-ID: <20171116184305.snpudnjdhua2obby@hirez.programming.kicks-ass.net>
References: <20171114200414.2188-1-mathieu.desnoyers@efficios.com>
 <20171114200414.2188-2-mathieu.desnoyers@efficios.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <20171114200414.2188-2-mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
Cc: "Paul E . McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Boqun Feng <boqun.feng-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>, Dave Watson <davejwatson-b10kYP2dOMg@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "H . Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Andrew Hunter <ahh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>, Chris Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>, Ben Maurer <bmaurer-b10kYP2dOMg@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
List-Id: linux-api@vger.kernel.org

On Tue, Nov 14, 2017 at 03:03:51PM -0500, Mathieu Desnoyers wrote:
> +/*
> + * If parent process has a registered restartable sequences area, the
> + * child inherits. Only applies when forking a process, not a thread. In
> + * case a parent fork() in the middle of a restartable sequence, set the
> + * resume notifier to force the child to retry.
> + */
> +static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags)
> +{
> +	if (clone_flags & CLONE_THREAD) {
> +		t->rseq = NULL;
> +		t->rseq_len = 0;
> +		t->rseq_sig = 0;
> +	} else {
> +		t->rseq = current->rseq;
> +		t->rseq_len = current->rseq_len;
> +		t->rseq_sig = current->rseq_sig;
> +		rseq_set_notify_resume(t);
> +	}
> +}

This hurts my brain... what happens if you fork a multi-threaded
process?

Do we fully inherit the TLS state of the calling thread?