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Subject: Re: Regression in kernel 4.13-rcX for 32-bit x86 system - bisected to
 commit fc8dffd379ca
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>
References: <0e25aebb-b501-b92b-3931-1646b009e8ef@lwfinger.net>
 <alpine.DEB.2.20.1708140920250.1865@nanos>
From: Larry Finger <Larry.Finger@lwfinger.net>
Message-ID: <17507917-1617-9d73-3058-bf2b3a29fb0f@lwfinger.net>
Date: Mon, 14 Aug 2017 14:42:45 -0500
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On 08/14/2017 02:21 AM, Thomas Gleixner wrote:
> On Mon, 14 Aug 2017, Larry Finger wrote:
> 
>> My Del Latitude D600 (single 32-bit CPU) shows the following locking message
>> when booted:
>>
>> ============================================
>> WARNING: possible recursive locking detected
>> 4.12.0-rc2-00029-gfc8dffd #159 Not tainted
>> --------------------------------------------
>> systemd-udevd/153 is trying to acquire lock:
>>   (cpu_hotplug_lock.rw_sem){.+.+.+}, at: [<c030fc26>] stop_machine+0x16/0x30
>>
>> but task is already holding lock:
>>   (cpu_hotplug_lock.rw_sem){.+.+.+}, at: [<c0234353>] mtrr_add_page+0x83/0x470
> 
> ....
> 
>>   cpus_read_lock+0x48/0x90
>>   ? stop_machine+0x16/0x30
>>   stop_machine+0x16/0x30
>>   mtrr_add_page+0x18b/0x470
>>   mtrr_add+0x3e/0x70
>   
>> This problem was bisected to commit fc8dffd379ca ("cpu/hotplug: Convert
>> hotplug locking to percpu rwsem"). I am very confident in the correctness of
>> the bisection.
> 
> Fix below.
> 
> Thanks,
> 
> 	tglx
> 
> 8<--------------------
> 
> diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
> index c5bb63be4ba1..40d5a8a75212 100644
> --- a/arch/x86/kernel/cpu/mtrr/main.c
> +++ b/arch/x86/kernel/cpu/mtrr/main.c
> @@ -237,6 +237,18 @@ set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type typ
>   	stop_machine(mtrr_rendezvous_handler, &data, cpu_online_mask);
>   }
>   
> +static void set_mtrr_cpuslocked(unsigned int reg, unsigned long base,
> +				unsigned long size, mtrr_type type)
> +{
> +	struct set_mtrr_data data = { .smp_reg = reg,
> +				      .smp_base = base,
> +				      .smp_size = size,
> +				      .smp_type = type
> +				    };
> +
> +	stop_machine_cpuslocked(mtrr_rendezvous_handler, &data, cpu_online_mask);
> +}
> +
>   static void set_mtrr_from_inactive_cpu(unsigned int reg, unsigned long base,
>   				      unsigned long size, mtrr_type type)
>   {
> @@ -370,7 +382,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
>   	/* Search for an empty MTRR */
>   	i = mtrr_if->get_free_region(base, size, replace);
>   	if (i >= 0) {
> -		set_mtrr(i, base, size, type);
> +		set_mtrr_cpuslocked(i, base, size, type);
>   		if (likely(replace < 0)) {
>   			mtrr_usage_table[i] = 1;
>   		} else {
> @@ -378,7 +390,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
>   			if (increment)
>   				mtrr_usage_table[i]++;
>   			if (unlikely(replace != i)) {
> -				set_mtrr(replace, 0, 0, 0);
> +				set_mtrr_cpuslocked(replace, 0, 0, 0);
>   				mtrr_usage_table[replace] = 0;
>   			}
>   		}
> @@ -506,7 +518,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
>   		goto out;
>   	}
>   	if (--mtrr_usage_table[reg] < 1)
> -		set_mtrr(reg, 0, 0, 0);
> +		set_mtrr_cpuslocked(reg, 0, 0, 0);
>   	error = reg;
>    out:
>   	mutex_unlock(&mtrr_mutex);
> 

That fix works for me.

Thanks,

Larry