linux-kernel - Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)

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Message-ID: <49066300.2176.1522249413336.JavaMail.zimbra@efficios.com>
Date:   Wed, 28 Mar 2018 11:03:33 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable
 sequences system call (v12)

----- On Mar 28, 2018, at 8:52 AM, Peter Zijlstra peterz@...radead.org wrote:

> On Wed, Mar 28, 2018 at 02:29:46PM +0200, Peter Zijlstra wrote:
>> > +static int rseq_get_rseq_cs(struct task_struct *t,
>> > +			    unsigned long *start_ip,
>> > +			    unsigned long *post_commit_offset,
>> > +			    unsigned long *abort_ip,
>> > +			    uint32_t *cs_flags)
>> > +{
> 
>> 
>> > +
>> > +	*cs_flags = rseq_cs.flags;
>> > +	*start_ip = rseq_cs.start_ip;
>> > +	*post_commit_offset = rseq_cs.post_commit_offset;
>> > +	*abort_ip = rseq_cs.abort_ip;
>> 
>> Then this becomes a straight struct assignment.
> 
> I initially suggested passing a structure instead of many arguments, but
> then recondidered, mostly because it will be inlined (due to having only
> the one caller) anyway. Still, maybe a struct will work better, I dunno.

I find the result of struct pointer argument cleaner indeed. I'll go for that
approach.

I'll memset rseq_cs to 0 in the following case though, because the caller
expects the content of the structure to be set when rseq_get_rseq_cs() succeeds.

static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
{
        struct rseq_cs __user *urseq_cs;
        unsigned long ptr;
        u32 __user *usig;
        u32 sig;
        int ret;

        ret = __get_user(ptr, &t->rseq->rseq_cs);
        if (ret)
                return ret;
        if (!ptr) {
                memset(rseq_cs, 0, sizeof(*rseq_cs));
                return 0;
        }

[...]

Thanks!

Mathieu


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