linux-kernel - Re: [PATCH] virtio_mmio: fix devm cleanup

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Date:   Tue, 12 Dec 2017 13:29:02 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        "Michael S . Tsirkin" <mst@...hat.com>,
        weiping zhang <zhangweiping@...ichuxing.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_mmio: fix devm cleanup

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@....com> 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.