Date: Tue, 24 Sep 2013 15:56:24 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Paul Mackerras <paulus@au1.ibm.com>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>, James Hogan <james.hogan@imgtec.com>,
        "James E.J. Bottomley" <jejb@parisc-linux.org>,
        Helge Deller <deller@gmx.de>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "David S. Miller" <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC GIT PULL] softirq: Consolidation and stack overrun fix
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On Tue, Sep 24, 2013 at 02:42:57PM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2013-09-24 at 04:44 +0200, Frederic Weisbecker wrote:
> > So the safest way to fix this is to unconditionally call do_softirq()
> > from irq_exit().
> > A performance penalty may come along but safety primes.
> > 
> > We should probably do that and work on longer term solutions (Kconfig
> > based arch switch, etc...)
> > for the next merge window?
> 
> As you prefer, though I'm keen on getting the "fast" version in RHEL7 if
> RH will take it :-)

So what is the fast version? Converting __do_softirq() to do_softirq()
unconditionally.

RH will accept any fix that goes upstream.

> 
> From the generic code POV, it's a one-liner #ifdef to select between
> do_softirq and __do_softirq() right ? Then it's up to the arch to
> #define I_CAN_DO_FAST !

I'd rather say #define I_CAN_DO_SAFE :)

But I guess the kind of symbol we want is some ARCH_HAS_IRQ_STACK_LOW_HANDLER

> 
> > I'll respin the series plus the regression fix, unless somebody has a
> > better solution.
> 
> Cheers,
> Ben.
> 
> 
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