Re: [PATCH 3/3] cpufreq: governor: Use kobject release() method to free dbs_data

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Kevin Hao <haokexin@gmail.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [PATCH 3/3] cpufreq: governor: Use kobject release() method to free dbs_data
Date: Wed, 13 Apr 2022 15:30:03 +0200	[thread overview]
Message-ID: <CAJZ5v0hb_gBBT=sqEiwA6HVPnkzTQusmv1-MMY9SQ9oZKFAq6g@mail.gmail.com> (raw)
In-Reply-To: <YlF30nI8nLR5Jnmf@pek-khao-d2>

On Sat, Apr 9, 2022 at 2:11 PM Kevin Hao <haokexin@gmail.com> wrote:
>
> On Sat, Feb 05, 2022 at 07:01:30PM +0800, Kevin Hao wrote:
> > On Fri, Feb 04, 2022 at 07:19:32PM +0100, Rafael J. Wysocki wrote:
> > > On Sun, Jan 23, 2022 at 1:49 PM Kevin Hao <haokexin@gmail.com> wrote:
> > > >
> > > > 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
> > > >
> > > > Fixes: c4435630361d ("cpufreq: governor: New sysfs show/store callbacks for governor tunables")
> > > > Signed-off-by: Kevin Hao <haokexin@gmail.com>
> > > > ---
> > > >  drivers/cpufreq/cpufreq_governor.c | 20 +++++++++++++-------
> > > >  drivers/cpufreq/cpufreq_governor.h |  1 +
> > > >  2 files changed, 14 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> > > > index 63f7c219062b..55c80319d268 100644
> > > > --- a/drivers/cpufreq/cpufreq_governor.c
> > > > +++ b/drivers/cpufreq/cpufreq_governor.c
> > > > @@ -388,6 +388,15 @@ static void free_policy_dbs_info(struct policy_dbs_info *policy_dbs,
> > > >         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);
> > > > @@ -425,6 +434,7 @@ int cpufreq_dbs_governor_init(struct cpufreq_policy *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);
> > > > @@ -447,6 +457,7 @@ int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
> > > >         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);
> > > > @@ -488,13 +499,8 @@ void cpufreq_dbs_governor_exit(struct cpufreq_policy *policy)
> > > >
> > > >         policy->governor_data = NULL;
> > > >
> > > > -       if (!count) {
> > > > -               if (!have_governor_per_policy())
> > > > -                       gov->gdbs_data = NULL;
> > > > -
> > > > -               gov->exit(dbs_data);
> > >
> > > Good catch, but it is unclear to me why gov->exit() cannot be called from here.
> >
> > The kobject_put(&attr_set->kobj) is invoked before this.
> >   cpufreq_dbs_governor_exit()
> >     gov_attr_set_put()
> >       kobject_put(&attr_set->kobj)
> >
> > When the CONFIG_DEBUG_KOBJECT_RELEASE is not enabled, the invocation of kobject_put() would
> > cause the dbs_data to be released immediately. So we have to move the gov->exit(dbs_data) before
> > the release of dbs_data.

I see, but the changelog is missing this information, so I've added
the following paragraph to it:

  Because dbs_data can be freed by the gov_attr_set_put() call
  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.

and queued it up for 5.19.

Thanks!