On 04-03-21, 15:07, Beata Michalska wrote:
> The current_opp when set, grabs additional reference on the opp,
> which is then supposed to be dropped upon releasing the opp table.
> Still both dev_pm_opp_remove_table and dev_pm_opp_remove_all_dynamic
> will completely drain the OPPs list, including dropping the additional
> reference on current_opp. This may lead to an attempt to access
> memory that has already been released. Make sure that while draining
> the list (in both dynamic and static cases) the current_opp gets
> actually invalidated.
>
> Fixes: 81c4d8a3c414 ("opp: Keep track of currently programmed OPP")
>
> Signed-off-by: Beata Michalska <beata.michal...@arm.com>
> ---
> drivers/opp/core.c | 49 ++++++++++++++++++++++++++++++++-----------------
> 1 file changed, 32 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index c268938..10e65c4 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1502,10 +1502,39 @@ static struct dev_pm_opp *_opp_get_next(struct
> opp_table *opp_table,
> return opp;
> }
>
> -bool _opp_remove_all_static(struct opp_table *opp_table)
> +static int __opp_drain_list(struct opp_table *opp_table, bool dynamic)
> {
> struct dev_pm_opp *opp;
> + int count = 0;
> +
> + /*
> + * Can't remove the OPP from under the lock, debugfs removal needs to
> + * happen lock less to avoid circular dependency issues.
> + */
> + while ((opp = _opp_get_next(opp_table, dynamic))) {
> + /*
> + * The current_opp has extra hold on the ref count,
> + * still the draining here will result in all of them
> + * being dropped completely, so make
> + * sure no one will try to access the current_opp
> + * afterwords
> + */
> + if (opp_table->current_opp == opp &&
> + !(kref_read(&opp->kref) - 1))
> + opp_table->current_opp = NULL;
Did you miss looking at:
static void _opp_table_kref_release(struct kref *kref)
{
...
if (opp_table->current_opp)
dev_pm_opp_put(opp_table->current_opp);
...
}
?
This is the place where the last reference to the current_opp is released and so
we shouldn't have any invalid access to it anywhere else.
Or am I missing some context here ?
--
viresh
