linux-kernel - Re: [PATCH 06/18] staging: gasket: fix deadlock in pci driver unregister path

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Date:   Sat, 14 Jul 2018 11:07:21 +0300
From:   Dmitry Torokhov <dtor@...omium.org>
To:     toddpoynor@...il.com
Cc:     rspringer@...gle.com, jnjoseph@...gle.com, benchan@...omium.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        frankhu@...omium.org, Simon Que <sque@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        devel@...verdev.osuosl.org, lkml <linux-kernel@...r.kernel.org>,
        toddpoynor@...gle.com
Subject: Re: [PATCH 06/18] staging: gasket: fix deadlock in pci driver
 unregister path

On Sat, Jul 14, 2018 at 8:58 AM Todd Poynor <toddpoynor@...il.com> wrote:
>
> From: Todd Poynor <toddpoynor@...gle.com>
>
> g_mutex held across pci_unregister_driver() call, also held in
> gasket_pci_remove(), which deadlocks.
>
> Reported-by: Dmitry Torokhov <dtor@...omium.org>
> Signed-off-by: Zhongze Hu <frankhu@...omium.org>
> Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
> ---
>  drivers/staging/gasket/gasket_core.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/staging/gasket/gasket_core.c b/drivers/staging/gasket/gasket_core.c
> index 3bdf7d36b397..6d240dc59557 100644
> --- a/drivers/staging/gasket/gasket_core.c
> +++ b/drivers/staging/gasket/gasket_core.c
> @@ -668,13 +668,10 @@ static void gasket_pci_remove(struct pci_dev *pci_dev)
>         struct gasket_dev *gasket_dev = NULL;
>         const struct gasket_driver_desc *driver_desc;
>         /* Find the device desc. */
> -       mutex_lock(&g_mutex);
> +       __must_hold(&g_mutex);

And what exactly ensures that mutex is held here? Yes, we are holding
the mutex when we unload the driver, but PCI hot-unplug or unbinding
the device though sysfs do not go through module unload code path, so
you'll end up here without holding the mutex.

>         internal_desc = lookup_internal_desc(pci_dev);
> -       if (!internal_desc) {
> -               mutex_unlock(&g_mutex);
> +       if (!internal_desc)
>                 return;
> -       }
> -       mutex_unlock(&g_mutex);
>
>         driver_desc = internal_desc->driver_desc;

Thanks,
Dmitry