Re: [PATCH v5 04/18] sparc32: mm: Reduce allocation size for PMD and PTE tables

[Mike Rapoport]

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@xxxxxxxxxx/

> 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
> > 
> 

-- 
Sincerely yours,
Mike.