Re: [PATCH] virtio_mmio: fix devm cleanup

From: Mark Rutland
Date: Tue Dec 12 2017 - 08:29:14 EST


On Tue, Dec 12, 2017 at 02:09:52PM +0100, Cornelia Huck wrote:
> On Tue, 12 Dec 2017 12:53:02 +0000
> Mark Rutland <mark.rutland@xxxxxxx> wrote:
>
> > Recent rework of the virtio_mmio probe path balanced a devm_ioremap()
> > with an iounmap() rather than its devm variant. This ends up corrupting
> > the devm datastructures, and results in the following boot failure on
> > arm64 under QEMU 2.9.0:
> >
> > [ 3.450397] ------------[ cut here ]------------
> > [ 3.453822] Trying to vfree() nonexistent vm area (00000000c05b4844)
> > [ 3.460534] WARNING: CPU: 1 PID: 1 at mm/vmalloc.c:1525 __vunmap+0x1b8/0x220
> > [ 3.475898] Kernel panic - not syncing: panic_on_warn set ...
> > [ 3.475898]
> > [ 3.493933] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc3 #1
> > [ 3.513109] Hardware name: linux,dummy-virt (DT)
> > [ 3.525382] Call trace:
> > [ 3.531683] dump_backtrace+0x0/0x368
> > [ 3.543921] show_stack+0x20/0x30
> > [ 3.547767] dump_stack+0x108/0x164
> > [ 3.559584] panic+0x25c/0x51c
> > [ 3.569184] __warn+0x29c/0x31c
> > [ 3.576023] report_bug+0x1d4/0x290
> > [ 3.586069] bug_handler.part.2+0x40/0x100
> > [ 3.597820] bug_handler+0x4c/0x88
> > [ 3.608400] brk_handler+0x11c/0x218
> > [ 3.613430] do_debug_exception+0xe8/0x318
> > [ 3.627370] el1_dbg+0x18/0x78
> > [ 3.634037] __vunmap+0x1b8/0x220
> > [ 3.648747] vunmap+0x6c/0xc0
> > [ 3.653864] __iounmap+0x44/0x58
> > [ 3.659771] devm_ioremap_release+0x34/0x68
> > [ 3.672983] release_nodes+0x404/0x880
> > [ 3.683543] devres_release_all+0x6c/0xe8
> > [ 3.695692] driver_probe_device+0x250/0x828
> > [ 3.706187] __driver_attach+0x190/0x210
> > [ 3.717645] bus_for_each_dev+0x14c/0x1f0
> > [ 3.728633] driver_attach+0x48/0x78
> > [ 3.740249] bus_add_driver+0x26c/0x5b8
> > [ 3.752248] driver_register+0x16c/0x398
> > [ 3.757211] __platform_driver_register+0xd8/0x128
> > [ 3.770860] virtio_mmio_init+0x1c/0x24
> > [ 3.782671] do_one_initcall+0xe0/0x398
> > [ 3.791890] kernel_init_freeable+0x594/0x660
> > [ 3.798514] kernel_init+0x18/0x190
> > [ 3.810220] ret_from_fork+0x10/0x18
>
> Oops.
>
> > To fix this, we can simply rip out the explicit cleanup that the devm
> > infrastructure will do for us when our probe function returns an error
> > code. We only need to ensure that we call put_device() if a call to
> > register_virtio_device() fails.
>
> OK, that was the subtility I obviously missed. Reading through the
> code, this seems correct (although I find the infrastructure a bit
> unintuitive).

No worries.

> Shouldn't the cleanup in _remove() then be removed as well?

Ah, I'd missed that.

I believe that can be removed, yes.

Should I spin a v2 with that folded in?

Thanks,
Mark.