linux-kernel - Re: [REGRESSION] RLIMIT

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Message-ID: <20160917090941.GB26044@uranus.lan>
Date:   Sat, 17 Sep 2016 12:09:41 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Konstantin Khlebnikov <koct9i@...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 11:33:56AM +0300, Konstantin Khlebnikov wrote:
> >
> > do_just_once just isn't a good name for a global
> > rate limited mechanism that does something very
> > different than the name.
> >
> > Maybe allow_once_per_ratelimit or the like
> >
> > There could be an equivalent do_once
> >
> > https://lkml.org/lkml/2009/5/22/3
> >
> 
> What about this printk_reriodic() and pr_warn_once_per_minute()?
> 
> It simply remembers next jiffies to print rather than using that
> complicated ratelimiting engine.

+#define printk_periodic(period, fmt, ...)                      \
+({                                                             \
+	static unsigned long __print_next __read_mostly = INITIAL_JIFFIES; \
+	bool __do_print = time_after_eq(jiffies, __print_next); \
+                                                               \
+	if (__do_print) {                                       \
+               __print_next = jiffies + (period);              \
+               printk(fmt, ##__VA_ARGS__);                     \
+	}                                                       \
+	unlikely(__do_print);                                   \
+})

Seems I don't understand the bottom unlikely...