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Date: Tue, 24 Mar 2009 22:34:36 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-tip-commits@vger.kernel.org, linux-kernel@vger.kernel.org,
       hpa@zytor.com, mingo@redhat.com, peterz@infradead.org, ia6432@inbox.ru,
       roland@redhat.com, tglx@linutronix.de
Subject: Re: [tip:timers/urgent] posix timers: fix RLIMIT_CPU && fork()
Message-ID: <20090324213436.GA22254@redhat.com>
References: <20090323193411.GA17514@redhat.com> <tip-37bebc70d7ad4144c571d74500db3bb26ec0c0eb@git.kernel.org> <20090324182651.GA13408@redhat.com> <20090324210536.GB14067@elte.hu>
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On 03/24, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > On 03/23, Oleg Nesterov wrote:
> > >
> > > Commit-ID:  37bebc70d7ad4144c571d74500db3bb26ec0c0eb
> > > Gitweb:     http://git.kernel.org/tip/37bebc70d7ad4144c571d74500db3bb26ec0c0eb
> > > Author:     Oleg Nesterov <oleg@redhat.com>
> > > AuthorDate: Mon, 23 Mar 2009 20:34:11 +0100
> > > Committer:  Ingo Molnar <mingo@elte.hu>
> > > CommitDate: Mon, 23 Mar 2009 20:43:35 +0100
> > >
> > > posix timers: fix RLIMIT_CPU && fork()
> > >
> > > See http://bugzilla.kernel.org/show_bug.cgi?id=12911
> > >
> > > copy_signal() copies signal->rlim, but RLIMIT_CPU is "lost". Because
> > > posix_cpu_timers_init_group() sets cputime_expires.prof_exp = 0 and thus
> > > fastpath_timer_check() returns false unless we have other cpu timers.
> > >
> > > This is the minimal fix for 2.6.29 (tested) and 2.6.28. The patch is not
> > > optimal,
> >
> > Ingo, please drop this patch, it is very suboptimal.
>
> suboptimal why?

Because this patch provokes the slow path on every tick if this process
has rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY, even if RLIMIT_CPU is
not expired yet.

So I think the initial patch I sent (which modifies copy_signal) is better,
but first I'd like to re-check the code once again.

Oleg.