On 27-10-20, 17:05, Viresh Kumar wrote: > It isn't that straight forward unfortunately, we need to make sure the > table doesn't get allocated for the same device twice, so > find+allocate needs to happen within a locked region. > > I have taken, not so straight forward, approach to fixing this issue, > lets see if this fixes it or not. > > -------------------------8<------------------------- > > diff --git a/drivers/opp/core.c b/drivers/opp/core.c > index 4ac4e7ce6b8b..6f4a73a6391f 100644 > --- a/drivers/opp/core.c > +++ b/drivers/opp/core.c > @@ -29,6 +29,8 @@ > LIST_HEAD(opp_tables); > /* Lock to allow exclusive modification to the device and opp lists */ > DEFINE_MUTEX(opp_table_lock); > +/* Flag indicating that opp_tables list is being updated at the moment */ > +static bool opp_tables_busy; > > static struct opp_device *_find_opp_dev(const struct device *dev, > struct opp_table *opp_table) > @@ -1036,8 +1038,8 @@ static void _remove_opp_dev(struct opp_device *opp_dev, > kfree(opp_dev); > } > > -static struct opp_device *_add_opp_dev_unlocked(const struct device *dev, > - struct opp_table *opp_table) > +struct opp_device *_add_opp_dev(const struct device *dev, > + struct opp_table *opp_table) > { > struct opp_device *opp_dev; > > @@ -1048,7 +1050,9 @@ static struct opp_device *_add_opp_dev_unlocked(const struct device *dev, > /* Initialize opp-dev */ > opp_dev->dev = dev; > > + mutex_lock(&opp_table->lock); > list_add(&opp_dev->node, &opp_table->dev_list); > + mutex_unlock(&opp_table->lock); > > /* Create debugfs entries for the opp_table */ > opp_debug_register(opp_dev, opp_table); > @@ -1056,18 +1060,6 @@ static struct opp_device *_add_opp_dev_unlocked(const struct device *dev, > return opp_dev; > } > > -struct opp_device *_add_opp_dev(const struct device *dev, > - struct opp_table *opp_table) > -{ > - struct opp_device *opp_dev; > - > - mutex_lock(&opp_table->lock); > - opp_dev = _add_opp_dev_unlocked(dev, opp_table); > - mutex_unlock(&opp_table->lock); > - > - return opp_dev; > -} > - > static struct opp_table *_allocate_opp_table(struct device *dev, int index) > { > struct opp_table *opp_table; > @@ -1121,8 +1113,6 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index) > INIT_LIST_HEAD(&opp_table->opp_list); > kref_init(&opp_table->kref); > > - /* Secure the device table modification */ > - list_add(&opp_table->node, &opp_tables); > return opp_table; > > err: > @@ -1135,27 +1125,64 @@ void _get_opp_table_kref(struct opp_table *opp_table) > kref_get(&opp_table->kref); > } > > +/* > + * We need to make sure that the OPP table for a device doesn't get added twice, > + * if this routine gets called in parallel with the same device pointer. > + * > + * The simplest way to enforce that is to perform everything (find existing > + * table and if not found, create a new one) under the opp_table_lock, so only > + * one creator gets access to the same. But that expands the critical section > + * under the lock and may end up causing circular dependencies with frameworks > + * like debugfs, interconnect or clock framework as they may be direct or > + * indirect users of OPP core. > + * > + * And for that reason we have to go for a bit tricky implementation here, which > + * uses the opp_tables_busy flag to indicate if another creator is in the middle > + * of adding an OPP table and others should wait for it to finish. > + */ > static struct opp_table *_opp_get_opp_table(struct device *dev, int index) > { > struct opp_table *opp_table; > > - /* Hold our table modification lock here */ > +again: > mutex_lock(&opp_table_lock); > > opp_table = _find_opp_table_unlocked(dev); > if (!IS_ERR(opp_table)) > goto unlock; > > + /* > + * The opp_tables list or an OPP table's dev_list is getting updated by > + * another user, wait for it to finish. > + */ > + if (unlikely(opp_tables_busy)) { > + mutex_unlock(&opp_table_lock); > + cpu_relax(); > + goto again; > + } > + > + opp_tables_busy = true; > opp_table = _managed_opp(dev, index); > + > + /* Drop the lock to reduce the size of critical section */ > + mutex_unlock(&opp_table_lock); > + > if (opp_table) { > - if (!_add_opp_dev_unlocked(dev, opp_table)) { > + if (!_add_opp_dev(dev, opp_table)) { > dev_pm_opp_put_opp_table(opp_table); > opp_table = ERR_PTR(-ENOMEM); > } > - goto unlock; > + > + mutex_lock(&opp_table_lock); > + } else { > + opp_table = _allocate_opp_table(dev, index); > + > + mutex_lock(&opp_table_lock); > + if (!IS_ERR(opp_table)) > + list_add(&opp_table->node, &opp_tables); > } > > - opp_table = _allocate_opp_table(dev, index); > + opp_tables_busy = false; > > unlock: > mutex_unlock(&opp_table_lock); > @@ -1181,6 +1208,10 @@ static void _opp_table_kref_release(struct kref *kref) > struct opp_device *opp_dev, *temp; > int i; > > + /* Drop the lock as soon as we can */ > + list_del(&opp_table->node); > + mutex_unlock(&opp_table_lock); > + > _of_clear_opp_table(opp_table); > > /* Release clk */ > @@ -1208,10 +1239,7 @@ static void _opp_table_kref_release(struct kref *kref) > > mutex_destroy(&opp_table->genpd_virt_dev_lock); > mutex_destroy(&opp_table->lock); > - list_del(&opp_table->node); > kfree(opp_table); > - > - mutex_unlock(&opp_table_lock); > } > > void dev_pm_opp_put_opp_table(struct opp_table *opp_table) Rob, Ping. -- viresh _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel