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Date:   Thu, 5 Aug 2021 13:05:16 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Kevin Hao <haokexin@gmail.com>
Cc:     "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v2] cpufreq: schedutil: Use kobject release() method to
 free sugov_tunables
Message-ID: <20210805073516.qzpzifjoqluqfwhy@vireshk-i7>
References: <20210805072917.8762-1-haokexin@gmail.com>
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On 05-08-21, 15:29, Kevin Hao 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 split the original sugov_tunables_free() into two functions,
> sugov_clear_global_tunables() is just used to clear the global_tunables
> and the new sugov_tunables_free() is used as kobj_type::release to
> release the sugov_tunables safely.
> 
> Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kevin Hao <haokexin@gmail.com>
> ---
> v2: Introduce sugov_clear_global_tunables() as suggested by Rafael.
> 
>  kernel/sched/cpufreq_schedutil.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 57124614363d..e7af18857371 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 *********************/
> @@ -639,12 +647,10 @@ static struct sugov_tunables *sugov_tunables_alloc(struct sugov_policy *sg_polic
>  	return tunables;
>  }
>  
> -static void sugov_tunables_free(struct sugov_tunables *tunables)
> +static void sugov_clear_global_tunables(void)
>  {
>  	if (!have_governor_per_policy())
>  		global_tunables = NULL;
> -
> -	kfree(tunables);
>  }
>  
>  static int sugov_init(struct cpufreq_policy *policy)
> @@ -707,7 +713,7 @@ static int sugov_init(struct cpufreq_policy *policy)
>  fail:
>  	kobject_put(&tunables->attr_set.kobj);
>  	policy->governor_data = NULL;
> -	sugov_tunables_free(tunables);
> +	sugov_clear_global_tunables();
>  
>  stop_kthread:
>  	sugov_kthread_stop(sg_policy);
> @@ -734,7 +740,7 @@ 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);
> +		sugov_clear_global_tunables();
>  
>  	mutex_unlock(&global_tunables_lock);

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh