From: Beata Michalska beata.michalska@arm.com

We are required to call dev_pm_opp_put() from outside of the opp_table->lock as debugfs removal needs to happen lock-less to avoid circular dependency issues.

commit cf1fac943c63 ("opp: Reduce the size of critical section in _opp_kref_release()") tried to fix that introducing a new routine _opp_get_next() which keeps returning OPPs that can be freed by the callers and this routine shall be called without holding the opp_table->lock.

Though the commit overlooked the fact that the OPPs can be referenced by other users as well and this routine will end up dropping references which were taken by other users and hence freeing the OPPs prematurely.

In effect, other users of the OPPs will end up having invalid pointers at hand. We didn't see any crash reports earlier as the exact situation never happened, though it is certainly possible.

We need a way to mark which OPPs are no longer referenced by the OPP core, so we don't drop extra references to them accidentally.

This commit adds another OPP flag, "removed", which is used to track this. And now we should never end up dropping extra references to the OPPs.

Cc: v5.11+ stable@vger.kernel.org # v5.11+ Fixes: cf1fac943c63 ("opp: Reduce the size of critical section in _opp_kref_release()") Signed-off-by: Beata Michalska beata.michalska@arm.com [ Viresh: Almost rewrote entire patch, added new "removed" field, rewrote commit log and added the correct Fixes tag. ] Co-developed-by: Viresh Kumar viresh.kumar@linaro.org Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- Sending it formally again so others don't miss it.

drivers/opp/core.c | 48 ++++++++++++++++++++++++---------------------- drivers/opp/opp.h | 2 ++ 2 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c index c2689386a906..1556998425d5 100644 --- a/drivers/opp/core.c +++ b/drivers/opp/core.c @@ -1492,7 +1492,11 @@ static struct dev_pm_opp *_opp_get_next(struct opp_table *opp_table,

mutex_lock(&opp_table->lock); list_for_each_entry(temp, &opp_table->opp_list, node) { - if (dynamic == temp->dynamic) { + /* + * Refcount must be dropped only once for each OPP by OPP core, + * do that with help of "removed" flag. + */ + if (!temp->removed && dynamic == temp->dynamic) { opp = temp; break; } @@ -1502,10 +1506,27 @@ 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) +/* + * Can't call dev_pm_opp_put() from under the lock as debugfs removal needs to + * happen lock less to avoid circular dependency issues. This routine must be + * called without the opp_table->lock held. + */ +static void _opp_remove_all(struct opp_table *opp_table, bool dynamic) { struct dev_pm_opp *opp;

+ while ((opp = _opp_get_next(opp_table, dynamic))) { + opp->removed = true; + dev_pm_opp_put(opp); + + /* Drop the references taken by dev_pm_opp_add() */ + if (dynamic) + dev_pm_opp_put_opp_table(opp_table); + } +} + +bool _opp_remove_all_static(struct opp_table *opp_table) +{ mutex_lock(&opp_table->lock);

if (!opp_table->parsed_static_opps) { @@ -1520,13 +1541,7 @@ bool _opp_remove_all_static(struct opp_table *opp_table)

mutex_unlock(&opp_table->lock);

- /* - * 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, false))) - dev_pm_opp_put(opp); - + _opp_remove_all(opp_table, false); return true; }

@@ -1539,25 +1554,12 @@ bool _opp_remove_all_static(struct opp_table *opp_table) void dev_pm_opp_remove_all_dynamic(struct device *dev) { struct opp_table *opp_table; - struct dev_pm_opp *opp; - int count = 0;

opp_table = _find_opp_table(dev); if (IS_ERR(opp_table)) return;

- /* - * 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, true))) { - dev_pm_opp_put(opp); - count++; - } - - /* Drop the references taken by dev_pm_opp_add() */ - while (count--) - dev_pm_opp_put_opp_table(opp_table); + _opp_remove_all(opp_table, true);

/* Drop the reference taken by _find_opp_table() */ dev_pm_opp_put_opp_table(opp_table); diff --git a/drivers/opp/opp.h b/drivers/opp/opp.h index 50fb9dced3c5..407c3bfe51d9 100644 --- a/drivers/opp/opp.h +++ b/drivers/opp/opp.h @@ -56,6 +56,7 @@ extern struct list_head opp_tables, lazy_opp_tables; * @dynamic: not-created from static DT entries. * @turbo: true if turbo (boost) OPP * @suspend: true if suspend OPP + * @removed: flag indicating that OPP's reference is dropped by OPP core. * @pstate: Device's power domain's performance state. * @rate: Frequency in hertz * @level: Performance level @@ -78,6 +79,7 @@ struct dev_pm_opp { bool dynamic; bool turbo; bool suspend; + bool removed; unsigned int pstate; unsigned long rate; unsigned int level;