On Friday, April 28, 2017 01:30:20 PM Lv Zheng wrote:
> For all frequent late stage acpi_get_table() clone invocations, we should
> only fix them altogether, otherwise, excessive acpi_put_table() could
> unexpectedly unmap the table used by the other users. Thus the current plan
> is to fix all acpi_get_table() clones together or to fix none of them.
I honestly don't think that fixing none of them is a valid option here.
> This prevents kernel developers from improving the late stage code quality
> without waiting for the ACPICA upstream to improve first.
>
> This patch adds a mechanism to stop decrementing validation count to
> prevent the table unmapping operations so that acpi_put_table() balance
> fixes can be done independently to each others.
>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx>
> ---
> drivers/acpi/acpica/tbutils.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpica/tbutils.c b/drivers/acpi/acpica/tbutils.c
> index 7abe665..b517bd0 100644
> --- a/drivers/acpi/acpica/tbutils.c
> +++ b/drivers/acpi/acpica/tbutils.c
> @@ -445,12 +445,18 @@ void acpi_tb_put_table(struct acpi_table_desc *table_desc)
>
> ACPI_FUNCTION_TRACE(acpi_tb_put_table);
>
> - if (table_desc->validation_count == 0) {
> + if ((table_desc->validation_count + 1) == 0) {
This means that validation_count has reached the maximum value, right?
> ACPI_WARNING((AE_INFO,
> - "Table %p, Validation count is zero before decrement\n",
> + "Table %p, Validation count is about to expire, decrement is unsafe\n",
> table_desc));
So why is it unsafe to decrement it?
> return_VOID;
> }
> + if (table_desc->validation_count == 0) {
> + ACPI_ERROR((AE_INFO,
> + "Table %p, Validation count is zero before decrement\n",
> + table_desc));
> + return_VOID;
> + }
> table_desc->validation_count--;
>
> if (table_desc->validation_count == 0) {
>
Thanks,
Rafael
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