On Fri, Dec 9, 2016 at 8:15 AM, Lv Zheng <lv.zheng@xxxxxxxxx> wrote:
> The following wrong commit triggers issues in acpi_get_table_with_size()
> users:
> Subject: ACPICA: Tables: Back port acpi_get_table_with_size() and
> early_acpi_os_unmap_memory() from Linux kernel
>
> The function is invented to be a replacement of acpi_get_table() during
> early stage so that the early mapped pointer will not be stored in ACPICA
> core and thus the late stage acpi_get_table() won't return a wrong pointer.
> However the mapping size is returned just because it is required by
> early_acpi_os_unmap_memory() to unmap the pointer during early stage.
>
> As the mapping size equals to the acpi_table_header.length
> (see acpi_tb_init_table_descriptor() and acpi_tb_validate_table()), when
> such a convenient result is returned, driver code will start to use it
> instead of accessing acpi_table_header to obtain the length.
>
> So the commit can trigger problems in such drivers as it returns 0 now. And
> it did bring a trouble to drivers/acpi/nfit/core.c. So before cleaning up
> the drivers, we should keep the old semantics of the API.
>
> This patch fixes the wrong commit by returning the acpi_table_header.length
> from acpi_get_table_with_size().
Well, the way this works isn't particularly straightforward.
Wouldn't it be better to simply drop the check (if it is redundant)
from the NFIT driver?
> Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx>
> ---
> drivers/acpi/osl.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 5bef0f65..d0b273f 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -445,8 +445,16 @@ void __ref acpi_os_unmap_memory(void *virt, acpi_size size)
>
> status = acpi_get_table(signature, instance, out_table);
> if (ACPI_SUCCESS(status)) {
> - /* No longer used by early_acpi_os_unmap_memory() */
> - *tbl_size = 0;
> + /*
> + * "tbl_size" is no longer used by
> + * early_acpi_os_unmap_memory(), but is still used by the
> + * ACPI table drivers. So sets it to the length of the
> + * table when the tbl_size is requested.
> + * "out_table" is not sanity checked as AE_BAD_PARAMETER
> + * is returned if it is NULL.
> + */
> + if (tbl_size && *out_table)
> + *tbl_size = (*out_table)->length;
> }
>
> return (status);
> --
> 1.7.10
>
Thanks,
Rafael
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