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Subject: Re: [PATCH v5 04/18] sparc32: mm: Reduce allocation size for PMD and
 PTE tables
To:     Mike Rapoport <rppt@kernel.org>
Cc:     Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        elver@google.com, tglx@linutronix.de, paulmck@kernel.org,
        mingo@kernel.org, peterz@infradead.org,
        "David S. Miller" <davem@davemloft.net>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <786c8e05-ac62-7c23-d29d-3afa0239c318@roeck-us.net>
Date:   Tue, 26 May 2020 10:15:38 -0700
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On 5/26/20 9:29 AM, Mike Rapoport wrote:
> On Tue, May 26, 2020 at 09:18:54AM -0700, Guenter Roeck wrote:
>> On 5/26/20 7:01 AM, Will Deacon wrote:
>>> On Tue, May 26, 2020 at 02:26:35PM +0100, Will Deacon wrote:
>>>> On Sun, May 24, 2020 at 03:32:56PM +0300, Mike Rapoport wrote:
>>>>> On Thu, May 21, 2020 at 04:02:11PM -0700, Guenter Roeck wrote:
>>>>>> On 5/20/20 12:51 PM, Mike Rapoport wrote:
>>>>>>> On Wed, May 20, 2020 at 12:03:31PM -0700, Guenter Roeck wrote:
>>>>>>>> With above patch applied on top of Ira's patch, I get:
>>>>>>>>
>>>>>>>> BUG: spinlock recursion on CPU#0, S01syslogd/139
>>>>>>>>  lock: 0xf5448350, .magic: dead4ead, .owner: S01syslogd/139, .owner_cpu: 0
>>>>>>>> CPU: 0 PID: 139 Comm: S01syslogd Not tainted 5.7.0-rc6-next-20200518-00002-gb178d2d56f29-dirty #1
>>>>>>>> [f0067a64 :
>>>>>>>> do_raw_spin_lock+0xa8/0xd8 ]
>>>>>>>> [f00d5034 :
>>>>>>>> copy_page_range+0x328/0x804 ]
>>>>>>>> [f0025be4 :
>>>>>>>> dup_mm+0x334/0x434 ]
>>>>>>>> [f0027124 :
>>>>>>>> copy_process+0x1224/0x12b0 ]
>>>>>>>> [f0027344 :
>>>>>>>> _do_fork+0x54/0x30c ]
>>>>>>>> [f0027670 :
>>>>>>>> do_fork+0x5c/0x6c ]
>>>>>>>> [f000de44 :
>>>>>>>> sparc_do_fork+0x18/0x38 ]
>>>>>>>> [f000b7f4 :
>>>>>>>> do_syscall+0x34/0x40 ]
>>>>>>>> [5010cd4c :
>>>>>>>> 0x5010cd4c ]
>>>>>>>>
>>>>>>>> Looks like yet another problem.
>>>>>>>
>>>>>>> I've checked the patch above on top of the mmots which already has Ira's
>>>>>>> patches and it booted fine. I've used sparc32_defconfig to build the
>>>>>>> kernel and qemu-system-sparc with default machine and CPU. 
>>>>>>>
>>>>>>
>>>>>> Try sparc32_defconfig+SMP.
>>>>>  
>>>>> I see a differernt problem, but this could be related:
>>>>>
>>>>> INIT: version 2.86 booting
>>>>> rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
>>>>> 	(detected by 0, t=5252 jiffies, g=-935, q=3)
>>>>> rcu: All QSes seen, last rcu_sched kthread activity 5252 (-68674--73926), jiffies_till_next_fqs=1, root ->qsmask 0x0
>>>>> rcu: rcu_sched kthread starved for 5252 jiffies! g-935 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
>>>>> rcu: 	Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior.
>>>>> rcu: RCU grace-period kthread stack dump:
>>>>> rcu_sched       R  running task        0    10      2 0x00000000
>>>>>
>>>>> I'm running a bit old debian [1] with qemu-img-sparc.
>>>>>
>>>>> My bisect pointed at commit 8c8f3156dd40 ("sparc32: mm: Reduce
>>>>> allocation size for PMD and PTE tables"). The commit ID is valid for
>>>>> next-20200522.
>>>>
>>>> Can you try the diff below please?
>>>
>>> Actually, that's racy. New version below!
>>>
>>
>> Applied on top of next-20200526, with defconfig+SMP, I still get:
>>
>> BUG: Bad page state in process swapper/0  pfn:0069f
>>
>> many times. Did I have to revert something else ? Sorry, I lost track.
>  
> The bad page messages are fixed by [1], but this is not in mmotm or
> linux-next. This is not related to SMP hangs.
> 
> [1] https://lore.kernel.org/lkml/20200524165358.27188-1-rppt@kernel.org/
> 

With that applied, all boot tests pass for me (including tests with
"-smp 2" on SS-10).

Guenter

>> Note that "-smp 2" on SS-10 works for me (with the same page state
>> messages).
>>
>> Guenter
>>
>>
>>> Will
>>>
>>> --->8
>>>
>>> diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
>>> index c861c0f0df73..068029471aa4 100644
>>> --- a/arch/sparc/mm/srmmu.c
>>> +++ b/arch/sparc/mm/srmmu.c
>>> @@ -363,11 +363,16 @@ pgtable_t pte_alloc_one(struct mm_struct *mm)
>>>  
>>>  	if ((ptep = pte_alloc_one_kernel(mm)) == 0)
>>>  		return NULL;
>>> +
>>>  	page = pfn_to_page(__nocache_pa((unsigned long)ptep) >> PAGE_SHIFT);
>>> -	if (!pgtable_pte_page_ctor(page)) {
>>> -		__free_page(page);
>>> -		return NULL;
>>> +
>>> +	spin_lock(&mm->page_table_lock);
>>> +	if (page_ref_inc_return(page) == 2 && !pgtable_pte_page_ctor(page)) {
>>> +		page_ref_dec(page);
>>> +		ptep = NULL;
>>>  	}
>>> +	spin_unlock(&mm->page_table_lock);
>>> +
>>>  	return ptep;
>>>  }
>>>  
>>> @@ -376,7 +381,12 @@ void pte_free(struct mm_struct *mm, pgtable_t ptep)
>>>  	struct page *page;
>>>  
>>>  	page = pfn_to_page(__nocache_pa((unsigned long)ptep) >> PAGE_SHIFT);
>>> -	pgtable_pte_page_dtor(page);
>>> +
>>> +	spin_lock(&mm->page_table_lock);
>>> +	if (page_ref_dec_return(page) == 1)
>>> +		pgtable_pte_page_dtor(page);
>>> +	spin_unlock(&mm->page_table_lock);
>>> +
>>>  	srmmu_free_nocache(ptep, SRMMU_PTE_TABLE_SIZE);
>>>  }
>>>  
>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>> index c1acc34c1c35..97458119cce8 100644
>>> --- a/mm/Kconfig
>>> +++ b/mm/Kconfig
>>> @@ -192,6 +192,9 @@ config MEMORY_HOTREMOVE
>>>  # Default to 4 for wider testing, though 8 might be more appropriate.
>>>  # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
>>>  # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
>>> +# SPARC32 allocates multiple pte tables within a single page, and therefore
>>> +# a per-page lock leads to problems when multiple tables need to be locked
>>> +# at the same time (e.g. copy_page_range()).
>>>  # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
>>>  #
>>>  config SPLIT_PTLOCK_CPUS
>>> @@ -199,6 +202,7 @@ config SPLIT_PTLOCK_CPUS
>>>  	default "999999" if !MMU
>>>  	default "999999" if ARM && !CPU_CACHE_VIPT
>>>  	default "999999" if PARISC && !PA20
>>> +	default "999999" if SPARC32
>>>  	default "4"
>>>  
>>>  config ARCH_ENABLE_SPLIT_PMD_PTLOCK
>>>
>>
>