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Date: Thu, 16 Nov 2017 19:43:05 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
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Subject: Re: [RFC PATCH v11 for 4.15 01/24] Restartable sequences system call
Message-ID: <20171116184305.snpudnjdhua2obby@hirez.programming.kicks-ass.net>
References: <20171114200414.2188-1-mathieu.desnoyers@efficios.com>
 <20171114200414.2188-2-mathieu.desnoyers@efficios.com>
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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?