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Date: Tue, 26 May 2020 14:26:35 +0100
From: Will Deacon <will@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
elver@...gle.com, tglx@...utronix.de, paulmck@...nel.org,
mingo@...nel.org, peterz@...radead.org,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v5 04/18] sparc32: mm: Reduce allocation size for PMD and
PTE tables
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:
> > >> On 5/20/20 10:03 AM, Mike Rapoport wrote:
> > >>> On Mon, May 18, 2020 at 09:37:15AM +0100, Will Deacon wrote:
> > >>>> On Sat, May 16, 2020 at 05:07:50PM -0700, Guenter Roeck wrote:
> > >>>>> On Sat, May 16, 2020 at 05:00:50PM -0700, Guenter Roeck wrote:
> > >>>>>> On Mon, May 11, 2020 at 09:41:36PM +0100, Will Deacon wrote:
> > >>>>>>> Now that the page table allocator can free page table allocations
> > >>>>>>> smaller than PAGE_SIZE, reduce the size of the PMD and PTE allocations
> > >>>>>>> to avoid needlessly wasting memory.
> > >>>>>>>
> > >>>>>>> Cc: "David S. Miller" <davem@...emloft.net>
> > >>>>>>> Cc: Peter Zijlstra <peterz@...radead.org>
> > >>>>>>> Signed-off-by: Will Deacon <will@...nel.org>
> > >>>>>>
> > >>>>>> Something in the sparc32 patches in linux-next causes all my sparc32 emulations
> > >>>>>> to crash. bisect points to this patch, but reverting it doesn't help, and neither
> > >>>>>> does reverting the rest of the series.
> > >>>>>>
> > >>>>> Actually, turns out I see the same pattern (lots of scheduling while atomic
> > >>>>> followed by 'killing interrupt handler' in cryptomgr_test) with several
> > >>>>> powerpc boot tests. I am currently bisecting those crashes. I'll report
> > >>>>> the results here as well as soon as I have it.
> > >>>>
> > >>>> FWIW, I retested my sparc32 patches with PREEMPT=y and I don't see any
> > >>>> issues. However, linux-next is a different story, where I don't get very far
> > >>>> at all:
> > >>>>
> > >>>> BUG: Bad page state in process swapper pfn:005b4
> > >>
> > >> 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?
Will
--->8
diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
index c861c0f0df73..7c05c0dea511 100644
--- a/arch/sparc/mm/srmmu.c
+++ b/arch/sparc/mm/srmmu.c
@@ -363,20 +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);
+ if (!PageTable(page) && !pgtable_pte_page_ctor(page))
return NULL;
- }
+
return ptep;
}
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);
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
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