Re: [PATCH] vboxguest: add missing devm_free_irq

From: Pascal Terjan <pterjan@google.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hans de Goede <hdegoede@redhat.com>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vboxguest: add missing devm_free_irq
Date: Fri, 10 Jun 2022 15:00:14 +0000	[thread overview]
Message-ID: <CAANdO=KDp9aYbRGxb4sDQtBD4rrjpy6_ruQBt9mZiVKtW_KZGw@mail.gmail.com> (raw)
In-Reply-To: <YqNMGgwsjhB7TNzk@kroah.com>

On Fri, 10 Jun 2022 at 13:50, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Thu, Jun 09, 2022 at 02:40:57PM +0100, Pascal Terjan wrote:
> > This fixes the following warning when unloading the module:
> >
> > [249348.837181] remove_proc_entry: removing non-empty directory 'irq/20', leaking at least 'vboxguest'
> > [249348.837219] WARNING: CPU: 0 PID: 6708 at fs/proc/generic.c:715 remove_proc_entry+0x119/0x140
> >
> > [249348.837379] Call Trace:
> > [249348.837385]  unregister_irq_proc+0xbd/0xe0
> > [249348.837392]  free_desc+0x23/0x60
> > [249348.837396]  irq_free_descs+0x4a/0x70
> > [249348.837401]  irq_domain_free_irqs+0x160/0x1a0
> > [249348.837452]  mp_unmap_irq+0x5c/0x60
> > [249348.837458]  acpi_unregister_gsi_ioapic+0x29/0x40
> > [249348.837463]  acpi_unregister_gsi+0x17/0x30
> > [249348.837467]  acpi_pci_irq_disable+0xbf/0xe0
> > [249348.837473]  pcibios_disable_device+0x20/0x30
> > [249348.837478]  pci_disable_device+0xef/0x120
> > [249348.837482]  vbg_pci_remove+0x6c/0x70 [vboxguest]
> >
> > Signed-off-by: Pascal Terjan <pterjan@google.com>
> > ---
> >  drivers/virt/vboxguest/vboxguest_linux.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/virt/vboxguest/vboxguest_linux.c b/drivers/virt/vboxguest/vboxguest_linux.c
> > index 6e8c0f1c1056..faa4bc9f625c 100644
> > --- a/drivers/virt/vboxguest/vboxguest_linux.c
> > +++ b/drivers/virt/vboxguest/vboxguest_linux.c
> > @@ -423,6 +423,7 @@ static void vbg_pci_remove(struct pci_dev *pci)
> >       vbg_gdev = NULL;
> >       mutex_unlock(&vbg_gdev_mutex);
> >
> > +     devm_free_irq(gdev->dev, pci->irq, gdev);
>
> The whope point of using devm_* calls is so you don't have to do stuff
> like this.  Perhaps this should not be using devm_() for the irq at all?

My initial assumption was that some sort of dependency was missing
somewhere to ensure this gets freed first, but I failed to find any
documentation on how this is supposed to work, so I went with a fix
that would work.

But you are obviously right, if we manually free it in the normal path
then using devm_{request,free}_irq sounds like just overhead without
benefits.