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From: Thomas Gleixner <tglx@linutronix.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Jeff Garzik" <jgarzik@pobox.com>,
	"Björn Steinbrink" <B.Steinbrink@gmx.de>,
	LKML <linux-kernel@vger.kernel.org>,
	"Ingo Molnar" <mingo@elte.hu>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()
Date: Mon, 25 Feb 2008 23:01:59 +0100 (CET)	[thread overview]
Message-ID: <alpine.LFD.1.00.0802252242290.7583@apollo.tec.linutronix.de> (raw)
In-Reply-To: <20080225124054.9b69e9f0.akpm@linux-foundation.org>

On Mon, 25 Feb 2008, Andrew Morton wrote:
> On Mon, 25 Feb 2008 15:08:35 -0500 Jeff Garzik <jgarzik@pobox.com> wrote:
> > There are plenty of drivers that do the same thing that ahci does, in 
> > terms of interrupt handler locking...  and I will definitely push back 
> > on efforts to convert otherwise-100%-safe spin_lock() into 
> > spin_lock_irqsave() just to quiet lockdep.
> > 
> > Very interesting email, thanks...
> > 
> 
> I suspect this is a bug in my old kmap_atomic debugging patch.  It doesn't
> know about the implicit irq-disablememnt which interrupt handlers enjoy.  I
> don't think...

I suspect here is confusion. The implicit irq-disablement of lockdep
is actually hiding the warning.

The code which emits the warning is:

        if (type == KM_IRQ0 || type == KM_IRQ1 || type == KM_BOUNCE_READ ||
                        type == KM_BIO_SRC_IRQ || type == KM_BIO_DST_IRQ) {
                if (!irqs_disabled()) {
                        WARN_ON(1);
                        warn_count--;
                }

It checks for _NOT_ irqs_disabled. The calling code is
ata_scsi_rbuf_get() which calls with:

     buf = kmap_atomic(sg_page(sg), KM_IRQ0) + sg->offset;

This happens with interrupts enabled. So the warning is according to
the well documented km_type enum and the equally well documented
highmem debug code correct.

Bjoern decoded it very well, just Jeff jumped to very interesting
conclusions.

Thanks,

	tglx

  reply	other threads:[~2008-02-25 22:03 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06 23:58 Thomas Gleixner
2008-02-13 22:39 ` Rafael J. Wysocki
2008-02-14  1:13   ` Thomas Gleixner
2008-02-25 19:59 ` Björn Steinbrink
2008-02-25 20:08   ` Jeff Garzik
2008-02-25 20:35     ` Björn Steinbrink
2008-02-25 20:40     ` Andrew Morton
2008-02-25 22:01       ` Thomas Gleixner [this message]
2008-02-25 22:17         ` Andrew Morton
2008-02-25 23:19         ` Jeff Garzik
2008-02-26  8:39           ` Ingo Molnar
2008-02-26 16:32             ` Jeff Garzik
2008-02-26 18:19               ` Andrew Morton
2008-02-26 20:49                 ` Ingo Molnar
2008-02-26 21:37                   ` Andrew Morton
2008-02-26 22:59                     ` Jeff Garzik
2008-02-27  0:02                       ` Alan Cox
2008-02-26 23:49                   ` Nick Piggin
2008-02-26  8:50           ` Thomas Gleixner

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