Date: Fri, 30 Jan 2009 21:49:33 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: roger.larsson@e-gatan.se, linux-kernel@vger.kernel.org, mingo@elte.hu,
       rml@tech9.net, pavel@ucw.cz, netdev@vger.kernel.org
Subject: Re: PROBLEM: in_atomic() misuse all over the place
Message-Id: <20090130214933.1b91ea3e.akpm@linux-foundation.org>
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	<87pri7k4id.fsf@basil.nowhere.org>
	<20090130160316.7e53ef99.akpm@linux-foundation.org>
	<20090131055508.GD18453@one.firstfloor.org>
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On Sat, 31 Jan 2009 06:55:08 +0100 Andi Kleen <andi@firstfloor.org> wrote:

> > There's a bit of a problem here.  If someone accidentally uses
> > gfp_any() inside a spinlock, it will do a sleeping allocation on
> > non-preempt kernels and will do an atomic allocation on preemptible
> > kernels, so we won't get to see the warning which would allow us to fix
> > the bug.
> 
> Yes exporting the function to drivers is dangerous I agree because
> it's easy to abuse.
> 
> > Would using irq_count() work?  If so, that would fix this up.
> 
> There's nothing that works reliably to detect spinlocks on non
> preempt kernels.

Hang on.  You said

  That's typically for softirq vs non softirq, which is important for
  the network stack.

that's what in_softirq() does.

Now, if networking is indeed using in_atomic() to detect
are-we-inside-a-spinlock then networking is buggy.

If networking is _not_ doing that then we can safely switch it to
in_sortirq() or in_interrupt().  And this would reenable the bug
detection which networking's use of in_atomic() accidentally
suppressed.


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