linux-kernel - Re: 2.6.24-git: kmap_atomic() WARN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 25 Feb 2008 23:01:59 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Jeff Garzik <jgarzik@...ox.com>,
	Björn Steinbrink <B.Steinbrink@....de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()

On Mon, 25 Feb 2008, Andrew Morton wrote:
> On Mon, 25 Feb 2008 15:08:35 -0500 Jeff Garzik <jgarzik@...ox.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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/