On Tuesday, May 09, 2017 01:57:41 PM Lv Zheng wrote:
> For all frequent late stage acpi_get_table() clone invocations, we should
> only change them altogether, otherwise, excessive acpi_put_table() could
> unexpectedly unmap the table used by the other users. Thus the current plan
> is to change all acpi_get_table() clones together or to change none of
> them. However in practical, this is not convenient as this can prevent
> kernel developers' efforts of improving the late stage code quality before
> waiting for the ACPICA upstream to improve first.
>
> This patch adds a validation count threashold, when it is reached, the
> validation count can no longer be incremented/decremented to invalidate the
> table descriptor (means preventing table unmappings) so that acpi_put_table()
> balance changes can be done independently to each others. Lv Zheng.
>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx>
> ---
> drivers/acpi/acpica/tbutils.c | 24 +++++++++++++++---------
> include/acpi/actbl.h | 9 +++++++++
> 2 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/acpi/acpica/tbutils.c b/drivers/acpi/acpica/tbutils.c
> index 7abe665..04beafc 100644
> --- a/drivers/acpi/acpica/tbutils.c
> +++ b/drivers/acpi/acpica/tbutils.c
> @@ -416,9 +416,13 @@ acpi_tb_get_table(struct acpi_table_desc *table_desc,
> }
> }
>
> - table_desc->validation_count++;
> - if (table_desc->validation_count == 0) {
> - table_desc->validation_count--;
> + if (table_desc->validation_count < ACPI_MAX_TABLE_VALIDATIONS) {
> + table_desc->validation_count++;
> + if (table_desc->validation_count >= ACPI_MAX_TABLE_VALIDATIONS) {
> + ACPI_WARNING((AE_INFO,
> + "Table %p, Validation count overflows\n",
> + table_desc));
> + }
> }
>
> *out_table = table_desc->pointer;
> @@ -445,13 +449,15 @@ void acpi_tb_put_table(struct acpi_table_desc *table_desc)
>
> ACPI_FUNCTION_TRACE(acpi_tb_put_table);
>
> - if (table_desc->validation_count == 0) {
> - ACPI_WARNING((AE_INFO,
> - "Table %p, Validation count is zero before decrement\n",
> - table_desc));
> - return_VOID;
> + if (table_desc->validation_count < ACPI_MAX_TABLE_VALIDATIONS) {
> + table_desc->validation_count--;
> + if (table_desc->validation_count >= ACPI_MAX_TABLE_VALIDATIONS) {
Is this going to ever trigger?
We've already verified that validation_count is not 0 and that it is less than
ACPI_MAX_TABLE_VALIDATIONS and we have decremented it, so how can it be
greater than or equal to ACPI_MAX_TABLE_VALIDATIONS here?
> + ACPI_WARNING((AE_INFO,
> + "Table %p, Validation count underflows\n",
> + table_desc));
> + return_VOID;
> + }
> }
> - table_desc->validation_count--;
>
> if (table_desc->validation_count == 0) {
>
Thanks,
Rafael
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