cpufreq: governor: Use kobject release() method to free dbs_data

The struct dbs_data embeds a struct gov_attr_set and
the struct gov_attr_set embeds a kobject. Since every kobject must have
a release() method and we can't use kfree() to free it directly,
so introduce cpufreq_dbs_data_release() to release the dbs_data via
the kobject::release() method. This fixes the calltrace like below:

ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x34
WARNING: CPU: 12 PID: 810 at lib/debugobjects.c:505 debug_print_object+0xb8/0x100
Modules linked in:
CPU: 12 PID: 810 Comm: sh Not tainted 5.16.0-next-20220120-yocto-standard+ #536
Hardware name: Marvell OcteonTX CN96XX board (DT)
pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : debug_print_object+0xb8/0x100
lr : debug_print_object+0xb8/0x100
sp : ffff80001dfcf9a0
x29: ffff80001dfcf9a0 x28: 0000000000000001 x27: ffff0001464f0000
x26: 0000000000000000 x25: ffff8000090e3f00 x24: ffff80000af60210
x23: ffff8000094dfb78 x22: ffff8000090e3f00 x21: ffff0001080b7118
x20: ffff80000aeb2430 x19: ffff800009e8f5e0 x18: 0000000000000000
x17: 0000000000000002 x16: 00004d62e58be040 x15: 013590470523aff8
x14: ffff8000090e1828 x13: 0000000001359047 x12: 00000000f5257d14
x11: 0000000000040591 x10: 0000000066c1ffea x9 : ffff8000080d15e0
x8 : ffff80000a1765a8 x7 : 0000000000000000 x6 : 0000000000000001
x5 : ffff800009e8c000 x4 : ffff800009e8c760 x3 : 0000000000000000
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0001474ed040
Call trace:
debug_print_object+0xb8/0x100
__debug_check_no_obj_freed+0x1d0/0x25c
debug_check_no_obj_freed+0x24/0xa0
kfree+0x11c/0x440
cpufreq_dbs_governor_exit+0xa8/0xac
cpufreq_exit_governor+0x44/0x90
cpufreq_set_policy+0x29c/0x570
store_scaling_governor+0x110/0x154
store+0xb0/0xe0
sysfs_kf_write+0x58/0x84
kernfs_fop_write_iter+0x12c/0x1c0
new_sync_write+0xf0/0x18c
vfs_write+0x1cc/0x220
ksys_write+0x74/0x100
__arm64_sys_write+0x28/0x3c
invoke_syscall.constprop.0+0x58/0xf0
do_el0_svc+0x70/0x170
el0_svc+0x54/0x190
el0t_64_sync_handler+0xa4/0x130
el0t_64_sync+0x1a0/0x1a4
irq event stamp: 189006
hardirqs last enabled at (189005): [<ffff8000080849d0>] finish_task_switch.isra.0+0xe0/0x2c0
hardirqs last disabled at (189006): [<ffff8000090667a4>] el1_dbg+0x24/0xa0
softirqs last enabled at (188966): [<ffff8000080106d0>] __do_softirq+0x4b0/0x6a0
softirqs last disabled at (188957): [<ffff80000804a618>] __irq_exit_rcu+0x108/0x1a4

[ rjw: Because can be freed by the gov_attr_set_put() in
cpufreq_dbs_governor_exit() now, it is also necessary to put the
invocation of the governor ->exit() callback into the new
cpufreq_dbs_data_release() function. ]

Fixes: c4435630361d ("cpufreq: governor: New sysfs show/store callbacks for governor tunables")
Signed-off-by: Kevin Hao <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/cpufreq_governor.c

···
 	gov->free(policy_dbs);
 }
 
+static void cpufreq_dbs_data_release(struct kobject *kobj)
+{
+	struct dbs_data *dbs_data = to_dbs_data(to_gov_attr_set(kobj));
+	struct dbs_governor *gov = dbs_data->gov;
+
+	gov->exit(dbs_data);
+	kfree(dbs_data);
+}
+
 int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
 {
 	struct dbs_governor *gov = dbs_governor_of(policy);
···
 		goto free_policy_dbs_info;
 	}
 
+	dbs_data->gov = gov;
 	gov_attr_set_init(&dbs_data->attr_set, &policy_dbs->list);
 
 	ret = gov->init(dbs_data);
···
 	policy->governor_data = policy_dbs;
 
 	gov->kobj_type.sysfs_ops = &governor_sysfs_ops;
+	gov->kobj_type.release = cpufreq_dbs_data_release;
 	ret = kobject_init_and_add(&dbs_data->attr_set.kobj, &gov->kobj_type,
 				   get_governor_parent_kobj(policy),
 				   "%s", gov->gov.name);
···
 
 	policy->governor_data = NULL;
 
-	if (!count) {
-		if (!have_governor_per_policy())
-			gov->gdbs_data = NULL;
-
-		gov->exit(dbs_data);
-		kfree(dbs_data);
-	}
+	if (!count && !have_governor_per_policy())
+		gov->gdbs_data = NULL;
 
 	free_policy_dbs_info(policy_dbs, gov);
 

drivers/cpufreq/cpufreq_governor.h

···
 /* Governor demand based switching data (per-policy or global). */
 struct dbs_data {
 	struct gov_attr_set attr_set;
+	struct dbs_governor *gov;
 	void *tuners;
 	unsigned int ignore_nice_load;
 	unsigned int sampling_rate;