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Date: Thu, 20 May 2021 21:13:36 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Daniel Scally <djrscally@...il.com>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Media Mailing List <linux-media@...r.kernel.org>,
"open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>, Yong Zhi <yong.zhi@...el.com>,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
Bingbu Cao <bingbu.cao@...el.com>,
Tianshu Qiu <tian.shu.qiu@...el.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Robert Moore <robert.moore@...el.com>,
Erik Kaneda <erik.kaneda@...el.com>
Subject: Re: [PATCH v1 1/1] ACPI: utils: Fix reference counting in for_each_acpi_dev_match()
On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> Currently it's possible to iterate over the dangling pointer in case the device
> suddenly disappears. This may happen becase callers put it at the end of a loop.
>
> Instead, let's move that call inside acpi_dev_get_next_match_dev().
Not really.
> Fixes: 803abec64ef9 ("media: ipu3-cio2: Add cio2-bridge to ipu3-cio2 driver")
> Fixes: bf263f64e804 ("media: ACPI / bus: Add acpi_dev_get_next_match_dev() and helper macro")
> Cc: Daniel Scally <djrscally@...il.com>
> Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Signed-off-by: Andy Shevchenko <andy.shevchenko@...il.com>
> ---
> drivers/acpi/utils.c | 5 +----
> drivers/media/pci/intel/ipu3/cio2-bridge.c | 8 +++-----
> include/acpi/acpi_bus.h | 5 -----
> 3 files changed, 4 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index 3b54b8fd7396..ccfc484dbffd 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -846,10 +846,6 @@ EXPORT_SYMBOL(acpi_dev_present);
> * Return the next match of ACPI device if another matching device was present
> * at the moment of invocation, or NULL otherwise.
> *
> - * FIXME: The function does not tolerate the sudden disappearance of @adev, e.g.
> - * in the case of a hotplug event. That said, the caller should ensure that
> - * this will never happen.
> - *
> * The caller is responsible for invoking acpi_dev_put() on the returned device.
> *
> * See additional information in acpi_dev_present() as well.
> @@ -866,6 +862,7 @@ acpi_dev_get_next_match_dev(struct acpi_device *adev, const char *hid, const cha
> match.hrv = hrv;
>
> dev = bus_find_device(&acpi_bus_type, start, &match, acpi_dev_match_cb);
> + acpi_dev_put(adev);
What's the point?
The caller may as well put it after this returns, can't it?
And what if the caller still wants to do something with adev after this returns?
> return dev ? to_acpi_device(dev) : NULL;
> }
> EXPORT_SYMBOL(acpi_dev_get_next_match_dev);
The original changelog is somewhat unclear. It should say that it is
required to reference-count the start-point device before passing it
to this function, but beyond that I don't see a bug here.
> diff --git a/drivers/media/pci/intel/ipu3/cio2-bridge.c b/drivers/media/pci/intel/ipu3/cio2-bridge.c
> index e8511787c1e4..477417261b6e 100644
> --- a/drivers/media/pci/intel/ipu3/cio2-bridge.c
> +++ b/drivers/media/pci/intel/ipu3/cio2-bridge.c
> @@ -178,13 +178,11 @@ static int cio2_bridge_connect_sensor(const struct cio2_sensor_config *cfg,
>
> if (bridge->n_sensors >= CIO2_NUM_PORTS) {
> dev_err(&cio2->dev, "Exceeded available CIO2 ports\n");
> - cio2_bridge_unregister_sensors(bridge);
> ret = -EINVAL;
> - goto err_out;
> + goto err_put_adev;
> }
>
> sensor = &bridge->sensors[bridge->n_sensors];
> - sensor->adev = adev;
> strscpy(sensor->name, cfg->hid, sizeof(sensor->name));
>
> ret = cio2_bridge_read_acpi_buffer(adev, "SSDB",
> @@ -214,6 +212,7 @@ static int cio2_bridge_connect_sensor(const struct cio2_sensor_config *cfg,
> goto err_free_swnodes;
> }
>
> + sensor->adev = acpi_dev_get(adev);
> adev->fwnode.secondary = fwnode;
>
> dev_info(&cio2->dev, "Found supported sensor %s\n",
> @@ -227,8 +226,7 @@ static int cio2_bridge_connect_sensor(const struct cio2_sensor_config *cfg,
> err_free_swnodes:
> software_node_unregister_nodes(sensor->swnodes);
> err_put_adev:
> - acpi_dev_put(sensor->adev);
> -err_out:
> + acpi_dev_put(adev);
> return ret;
> }
>
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 3a82faac5767..bff6a11bb21f 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -698,11 +698,6 @@ acpi_dev_get_first_match_dev(const char *hid, const char *uid, s64 hrv);
> * @hrv: Hardware Revision of the device, pass -1 to not check _HRV
> *
> * The caller is responsible for invoking acpi_dev_put() on the returned device.
> - *
> - * FIXME: Due to above requirement there is a window that may invalidate @adev
> - * and next iteration will use a dangling pointer, e.g. in the case of a
> - * hotplug event. That said, the caller should ensure that this will never
> - * happen.
> */
> #define for_each_acpi_dev_match(adev, hid, uid, hrv) \
> for (adev = acpi_dev_get_first_match_dev(hid, uid, hrv); \
> --
> 2.31.1
>
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