linux-kernel - Re: [PATCH for 5.5 1/2] rseq: Fix: Clarify rseq.h UAPI rseq

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Date:   Fri, 20 Dec 2019 21:37:59 +0100
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, stable@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Neel Natu <neelnatu@...gle.com>
Subject: Re: [PATCH for 5.5 1/2] rseq: Fix: Clarify rseq.h UAPI rseq_cs memory reclaim requirements

* Mathieu Desnoyers:

> diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
> index 9a402fdb60e9..6f26b0b148a6 100644
> --- a/include/uapi/linux/rseq.h
> +++ b/include/uapi/linux/rseq.h
> @@ -100,7 +100,9 @@ struct rseq {
>  	 * instruction sequence block, as well as when the kernel detects that
>  	 * it is preempting or delivering a signal outside of the range
>  	 * targeted by the rseq_cs. Also needs to be set to NULL by user-space
> -	 * before reclaiming memory that contains the targeted struct rseq_cs.
> +	 * before reclaiming memory that contains the targeted struct rseq_cs
> +	 * or reclaiming memory that contains the code refered to by the
> +	 * start_ip and post_commit_offset fields of struct rseq_cs.

Maybe mention that it's good practice to clear rseq_cs before
returning from a function that contains a restartable sequence?

That will deal with the dlclose issue because even if the function
calls dlclose itself, unmapping something on call stack for dlclose is
already undefined.