Re: [PATCH] cpufreq: schedutil: Use kobject release() method to free sugov_tunables

[Kevin Hao]

On Wed, Aug 04, 2021 at 06:54:10PM +0200, Rafael J. Wysocki wrote:
> On Thu, Jul 15, 2021 at 11:56 AM Kevin Hao <haokexin@xxxxxxxxx> wrote:
> >
> > The struct sugov_tunables is protected by the kobject, so we can't free
> > it directly. Otherwise we would get a call trace like this:
> >   ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x30
> >   WARNING: CPU: 3 PID: 720 at lib/debugobjects.c:505 debug_print_object+0xb8/0x100
> >   Modules linked in:
> >   CPU: 3 PID: 720 Comm: a.sh Tainted: G        W         5.14.0-rc1-next-20210715-yocto-standard+ #507
> >   Hardware name: Marvell OcteonTX CN96XX board (DT)
> >   pstate: 40400009 (nZcv daif +PAN -UAO -TCO BTYPE=--)
> >   pc : debug_print_object+0xb8/0x100
> >   lr : debug_print_object+0xb8/0x100
> >   sp : ffff80001ecaf910
> >   x29: ffff80001ecaf910 x28: ffff00011b10b8d0 x27: ffff800011043d80
> >   x26: ffff00011a8f0000 x25: ffff800013cb3ff0 x24: 0000000000000000
> >   x23: ffff80001142aa68 x22: ffff800011043d80 x21: ffff00010de46f20
> >   x20: ffff800013c0c520 x19: ffff800011d8f5b0 x18: 0000000000000010
> >   x17: 6e6968207473696c x16: 5f72656d6974203a x15: 6570797420746365
> >   x14: 6a626f2029302065 x13: 303378302f307830 x12: 2b6e665f72656d69
> >   x11: ffff8000124b1560 x10: ffff800012331520 x9 : ffff8000100ca6b0
> >   x8 : 000000000017ffe8 x7 : c0000000fffeffff x6 : 0000000000000001
> >   x5 : ffff800011d8c000 x4 : ffff800011d8c740 x3 : 0000000000000000
> >   x2 : ffff0001108301c0 x1 : ab3c90eedf9c0f00 x0 : 0000000000000000
> >   Call trace:
> >    debug_print_object+0xb8/0x100
> >    __debug_check_no_obj_freed+0x1c0/0x230
> >    debug_check_no_obj_freed+0x20/0x88
> >    slab_free_freelist_hook+0x154/0x1c8
> >    kfree+0x114/0x5d0
> >    sugov_exit+0xbc/0xc0
> >    cpufreq_exit_governor+0x44/0x90
> >    cpufreq_set_policy+0x268/0x4a8
> >    store_scaling_governor+0xe0/0x128
> >    store+0xc0/0xf0
> >    sysfs_kf_write+0x54/0x80
> >    kernfs_fop_write_iter+0x128/0x1c0
> >    new_sync_write+0xf0/0x190
> >    vfs_write+0x2d4/0x478
> >    ksys_write+0x74/0x100
> >    __arm64_sys_write+0x24/0x30
> >    invoke_syscall.constprop.0+0x54/0xe0
> >    do_el0_svc+0x64/0x158
> >    el0_svc+0x2c/0xb0
> >    el0t_64_sync_handler+0xb0/0xb8
> >    el0t_64_sync+0x198/0x19c
> >   irq event stamp: 5518
> >   hardirqs last  enabled at (5517): [<ffff8000100cbd7c>] console_unlock+0x554/0x6c8
> >   hardirqs last disabled at (5518): [<ffff800010fc0638>] el1_dbg+0x28/0xa0
> >   softirqs last  enabled at (5504): [<ffff8000100106e0>] __do_softirq+0x4d0/0x6c0
> >   softirqs last disabled at (5483): [<ffff800010049548>] irq_exit+0x1b0/0x1b8
> >
> > So add a release() method for sugov_tunables_ktype to release the
> > sugov_tunables safely.
> >
> > Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Kevin Hao <haokexin@xxxxxxxxx>
> > ---
> >  kernel/sched/cpufreq_schedutil.c | 23 ++++++++++++-----------
> >  1 file changed, 12 insertions(+), 11 deletions(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 57124614363d..ac171496da4b 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -537,9 +537,17 @@ static struct attribute *sugov_attrs[] = {
> >  };
> >  ATTRIBUTE_GROUPS(sugov);
> >
> > +static void sugov_tunables_free(struct kobject *kobj)
> > +{
> > +       struct gov_attr_set *attr_set = container_of(kobj, struct gov_attr_set, kobj);
> > +
> > +       kfree(to_sugov_tunables(attr_set));
> > +}
> > +
> >  static struct kobj_type sugov_tunables_ktype = {
> >         .default_groups = sugov_groups,
> >         .sysfs_ops = &governor_sysfs_ops,
> > +       .release = &sugov_tunables_free,
> >  };
> >
> >  /********************** cpufreq governor interface *********************/
> > @@ -639,14 +647,6 @@ static struct sugov_tunables *sugov_tunables_alloc(struct sugov_policy *sg_polic
> >         return tunables;
> >  }
> >
> > -static void sugov_tunables_free(struct sugov_tunables *tunables)
> 
> Rename this to sugov_clear_global_tunables() and make it take no arguments.

OK.

> 
> > -{
> > -       if (!have_governor_per_policy())
> > -               global_tunables = NULL;
> > -
> > -       kfree(tunables);
> 
> Drop just this one line from it.

OK.

> 
> > -}
> > -
> >  static int sugov_init(struct cpufreq_policy *policy)
> >  {
> >         struct sugov_policy *sg_policy;
> > @@ -707,7 +707,8 @@ static int sugov_init(struct cpufreq_policy *policy)
> >  fail:
> >         kobject_put(&tunables->attr_set.kobj);
> >         policy->governor_data = NULL;
> > -       sugov_tunables_free(tunables);
> 
> And call sugov_clear_global_tunables() instead of the above from here
> and analogously below.

Will do.

Thanks,
Kevin

> 
> > +       if (!have_governor_per_policy())
> > +               global_tunables = NULL;
> >
> >  stop_kthread:
> >         sugov_kthread_stop(sg_policy);
> > @@ -733,8 +734,8 @@ static void sugov_exit(struct cpufreq_policy *policy)
> >
> >         count = gov_attr_set_put(&tunables->attr_set, &sg_policy->tunables_hook);
> >         policy->governor_data = NULL;
> > -       if (!count)
> > -               sugov_tunables_free(tunables);
> > +       if (!count && !have_governor_per_policy())
> > +               global_tunables = NULL;
> >
> >         mutex_unlock(&global_tunables_lock);
> >
> > --

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