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@xxxxxxxxxx> wrote: >> On Wed, May 19, 2021 at 11:19 PM Andy Shevchenko >> <andy.shevchenko@xxxxxxxxx> 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@xxxxxxxxx> >>> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> >>> Signed-off-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> >>> --- >>> 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);