linux-kernel - Re: [REGRESSION] RLIMIT

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Message-ID: <CALYGNiN-ELbwSV0X2_FeKvGSOfRuHMsBnBDj86NHZxQKnZgVsQ@mail.gmail.com>
Date:   Sun, 18 Sep 2016 00:40:37 +0300
From:   Konstantin Khlebnikov <koct9i@...il.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sam Varshavchik <mrsam@...rier-mta.com>,
        Ingo Molnar <mingo@...nel.org>,
        Laura Abbott <labbott@...hat.com>, Brent <fix@...realm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] RLIMIT_DATA crashes named

On Sat, Sep 17, 2016 at 3:20 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> On Sat, Sep 17, 2016 at 03:09:09PM +0300, Konstantin Khlebnikov wrote:
>> >
>> > Seems I don't understand the bottom unlikely...
>>
>> This is gcc extrension:  https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
>> Here macro works as a function which returns bool
>
> no, no, I know for what unlikely extension stand for.
> it was just hard to obtain from without the context.
> this extension implies someone calls for
> if (printk_periodic()) right?

Yep.


Here is perfect macro for that jiffies check: time_in_range_open.

/*
 * Calculate whether a is in the range of [b, c).
 */
#define time_in_range_open(a,b,c) \
(time_after_eq(a,b) && \
time_before(a,c))

So... better version looks like

#define printk_periodic(period, fmt, ...)
({
        static unsigned long __prev __read_mostly = INITIAL_JIFFIES - (period);
        unsigned long __now = jiffies;
        bool __print = !time_in_range_open(__now, __prev, __prev + (period));

        if (__print) {
                __prev = __now;
                printk(fmt, ##__VA_ARGS__);
        }
        unlikely(__print);
})

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