linux-kernel - Re: Restartable Sequences system call merged into Linux

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Message-ID: <305409897.10888.1528747473727.JavaMail.zimbra@efficios.com>
Date:   Mon, 11 Jun 2018 16:04:33 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Carlos O'Donell <carlos@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        libc-alpha <libc-alpha@...rceware.org>
Subject: Re: Restartable Sequences system call merged into Linux

----- On Jun 11, 2018, at 3:55 PM, Florian Weimer fweimer@...hat.com wrote:

> On 06/11/2018 09:49 PM, Mathieu Desnoyers wrote:
>> It should be noted that there can be only one rseq TLS area registered per
>> thread,
>> which can then be used by many libraries and by the executable, so this is a
>> process-wide (per-thread) resource that we need to manage carefully.
> 
> Is it possible to resize the area after thread creation, perhaps even
> from other threads?

I'm not sure why we would want to resize it. The per-thread area is fixed-size.
Its layout is here: include/uapi/linux/rseq.h: struct rseq

The ABI is designed so that all users (program and libraries) can interact
through this per-thread TLS area.

> 
> If there is only one contiguous area, this generally means there needs
> to be linker support, similar to what we have for initial-exec TLS today.

Not entirely sure what you imply by "one contiguous area". All we need is
a single fixed-size TLS area for each thread.

Thanks,

Mathieu

> 
> Thanks,
> Florian

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com