3.16rc3 multiplatform, Armada 370 and IOMMU: unbootable kernel

Thomas Petazzoni thomas.petazzoni at free-electrons.com
Thu Jul 3 13:52:44 PDT 2014


On Thu, 03 Jul 2014 22:22:29 +0200, Gregory CLEMENT wrote:

> > Thanks for reporting the issue. Just to make it easy to reproduce the
> > problem, could post the complete .config that exhibits the issue?
> > 
> I managed to reproduced the hang with the configuration joined.
> As you can in my .config see I also activated earlyprintk to have more
> trace. The problem seems to come to something at the interaction between
> PCIe and IOMMU:

Thanks for reproducing the problem. In my opinion, the problem is in
drivers/iommu/omap-iommu.c, which gets compiled when
CONFIG_OMAP_IOMMU=y. This file does:

static int __init omap_iommu_init(void)
        struct kmem_cache *p;
        const unsigned long flags = SLAB_HWCACHE_ALIGN;
        size_t align = 1 << 10; /* L2 pagetable alignement */

        p = kmem_cache_create("iopte_cache", IOPTE_TABLE_SIZE, align, flags,
        if (!p)
                return -ENOMEM;
        iopte_cachep = p;

        bus_set_iommu(&platform_bus_type, &omap_iommu_ops);

        return platform_driver_register(&omap_iommu_driver);
/* must be ready before omap3isp is probed */

So it calls bus_set_iommu() unconditionally, without caring at all
whether it is running on a platform that actually cares about OMAP
IOMMU. And then later on, a bus notifier of the IOMMU subsystem gets
called, and some NULL pointer gets dereferenced. I'm pretty sure that
if you comment out this subsys_initcall(), you won't see the problem

However, this code has been around since a while, so I don't know if
it's actually the change that makes it visible. Maybe some other IOMMU
core internal change makes it actually visible. But this
subsys_initcall() that does random stuff without caring about the
platform it runs on anyway looks incorrect.

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering

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