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Date: Tue, 13 Jul 2021 23:32:28 +0100
From: Daniel Scally <djrscally@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-efi@...r.kernel.org, linux-media@...r.kernel.org,
devel@...ica.org
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>, Ard Biesheuvel <ardb@...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 v2 1/1] ACPI: utils: Fix reference counting in
for_each_acpi_dev_match()
Hi Andy - thanks for fixing this
On 12/07/2021 19:21, Andy Shevchenko 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().
>
> 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")
> Fixes: edbd1bc4951e ("efi/dev-path-parser: Switch to use for_each_acpi_dev_match()")
> Signed-off-by: Andy Shevchenko <andy.shevchenko@...il.com>
Reviewed-by: Daniel Scally <djrscally@...il.com>
> ---
> v2:
> - rebased on top of v5.14-rc1 and hence added fix for EFI code
> - added kernel documentation update to point out that
> acpi_dev_get_next_match_dev() drops a reference on the given
> ACPI device (Rafael)
>
> drivers/acpi/utils.c | 7 +++----
> drivers/firmware/efi/dev-path-parser.c | 1 -
> drivers/media/pci/intel/ipu3/cio2-bridge.c | 6 ++----
> include/acpi/acpi_bus.h | 5 -----
> 4 files changed, 5 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index e7ddd281afff..d5cedffeeff9 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -860,11 +860,9 @@ 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.
> + * On the other hand the function invokes acpi_dev_put() on the given @adev
> + * assuming that its reference counter had been increased beforehand.
> *
> * See additional information in acpi_dev_present() as well.
> */
> @@ -880,6 +878,7 @@ 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);
> return dev ? to_acpi_device(dev) : NULL;
> }
> EXPORT_SYMBOL(acpi_dev_get_next_match_dev);
> diff --git a/drivers/firmware/efi/dev-path-parser.c b/drivers/firmware/efi/dev-path-parser.c
> index 10d4457417a4..eb9c65f97841 100644
> --- a/drivers/firmware/efi/dev-path-parser.c
> +++ b/drivers/firmware/efi/dev-path-parser.c
> @@ -34,7 +34,6 @@ static long __init parse_acpi_path(const struct efi_dev_path *node,
> break;
> if (!adev->pnp.unique_id && node->acpi.uid == 0)
> break;
> - acpi_dev_put(adev);
> }
> if (!adev)
> return -ENODEV;
> diff --git a/drivers/media/pci/intel/ipu3/cio2-bridge.c b/drivers/media/pci/intel/ipu3/cio2-bridge.c
> index 4657e99df033..59a36f922675 100644
> --- a/drivers/media/pci/intel/ipu3/cio2-bridge.c
> +++ b/drivers/media/pci/intel/ipu3/cio2-bridge.c
> @@ -173,10 +173,8 @@ static int cio2_bridge_connect_sensor(const struct cio2_sensor_config *cfg,
> int ret;
>
> for_each_acpi_dev_match(adev, cfg->hid, NULL, -1) {
> - if (!adev->status.enabled) {
> - acpi_dev_put(adev);
> + if (!adev->status.enabled)
> continue;
> - }
>
> if (bridge->n_sensors >= CIO2_NUM_PORTS) {
> acpi_dev_put(adev);
> @@ -185,7 +183,6 @@ static int cio2_bridge_connect_sensor(const struct cio2_sensor_config *cfg,
> }
>
> 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",
> @@ -215,6 +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",
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 1ae993fee4a5..b9d434a93632 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -707,11 +707,6 @@ 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); \
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