| Message ID | 20210519210253.3578025-1-andy.shevchenko@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | [v1,1/1] ACPI: utils: Fix reference counting in for_each_acpi_dev_match() | expand |
On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko <andy.shevchenko@gmail.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@gmail.com> > Cc: Sakari Ailus <sakari.ailus@linux.intel.com> > Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.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 >
On Thu, May 20, 2021 at 9:13 PM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko > <andy.shevchenko@gmail.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. OK, I see what you want to achieve and the macro is actually buggy, because it leaves unbalanced references behind. > > 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@gmail.com> > > Cc: Sakari Ailus <sakari.ailus@linux.intel.com> > > Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.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. But the kerneldoc really needs to say that the caller is required to obtain a reference on adev before passing it here, because that reference will be dropped and the object pointed to by adev may not be present any more after this returns. > > @@ -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);
Hi Rafael, Andy On 20/05/2021 20:40, Rafael J. Wysocki wrote: > On Thu, May 20, 2021 at 9:13 PM Rafael J. Wysocki <rafael@kernel.org> wrote: >> On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko >> <andy.shevchenko@gmail.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. > OK, I see what you want to achieve and the macro is actually buggy, > because it leaves unbalanced references behind. Yeah; I guess the originally intended use (which was "get all these devices") doesn't really tally with the naming or with the operation of similar functions in the kernel like the fwnode_handle ops; sorry about that. Anyway; I think Andy's fix is the right way to do it, so the calling code's responsible for holding onto a reference if it wants to keep it. > >>> 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@gmail.com> >>> Cc: Sakari Ailus <sakari.ailus@linux.intel.com> >>> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.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. > But the kerneldoc really needs to say that the caller is required to > obtain a reference on adev before passing it here, because that > reference will be dropped and the object pointed to by adev may not be > present any more after this returns. > >>> @@ -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);
On Wed, May 26, 2021 at 1:29 AM Daniel Scally <djrscally@gmail.com> wrote: > On 20/05/2021 20:40, Rafael J. Wysocki wrote: > > On Thu, May 20, 2021 at 9:13 PM Rafael J. Wysocki <rafael@kernel.org> wrote: > >> On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko > >> <andy.shevchenko@gmail.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. > > OK, I see what you want to achieve and the macro is actually buggy, > > because it leaves unbalanced references behind. > > > Yeah; I guess the originally intended use (which was "get all these > devices") doesn't really tally with the naming or with the operation of > similar functions in the kernel like the fwnode_handle ops; sorry about > that. Anyway; I think Andy's fix is the right way to do it, so the > calling code's responsible for holding onto a reference if it wants to > keep it. I think we need to postpone the fix till v5.14-rc1 is out. It appears that some code has been changed in EFI and media subsystems so that patch will be in conflict with.
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); return dev ? to_acpi_device(dev) : NULL; } EXPORT_SYMBOL(acpi_dev_get_next_match_dev); 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); \
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") Cc: Daniel Scally <djrscally@gmail.com> Cc: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.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(-)