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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	linux-mm@kvack.org, Vineet Gupta <vgupta@synopsys.com>,
	akpm@linux-foundation.org,
	"linux-snps-arc@lists.infradead.org"
	<linux-snps-arc@lists.infradead.org>,
	linuxppc-dev@lists.ozlabs.org,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>
Subject: Re: [PATCH v4 00/13] mm/debug_vm_pgtable fixes
Date: Wed, 9 Sep 2020 14:08:55 +0530
Message-ID: <c6f4857e-4523-ad32-cbc1-fee417fc3f37@arm.com> (raw)
In-Reply-To: <20200904195346.6d57ff9f@thinkpad>

On 09/04/2020 11:23 PM, Gerald Schaefer wrote:
> On Fri, 4 Sep 2020 18:01:15 +0200
> Gerald Schaefer <gerald.schaefer@linux.ibm.com> wrote:
> 
>> On Fri, 4 Sep 2020 17:26:47 +0200
>> Gerald Schaefer <gerald.schaefer@linux.ibm.com> wrote:
>>
>>> On Fri, 4 Sep 2020 12:18:05 +0530
>>> Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>>
>>>>
>>>>
>>>> On 09/02/2020 05:12 PM, Aneesh Kumar K.V wrote:
>>>>> This patch series includes fixes for debug_vm_pgtable test code so that
>>>>> they follow page table updates rules correctly. The first two patches introduce
>>>>> changes w.r.t ppc64. The patches are included in this series for completeness. We can
>>>>> merge them via ppc64 tree if required.
>>>>>
>>>>> Hugetlb test is disabled on ppc64 because that needs larger change to satisfy
>>>>> page table update rules.
>>>>>
>>>>> These tests are broken w.r.t page table update rules and results in kernel
>>>>> crash as below. 
>>>>>
>>>>> [   21.083519] kernel BUG at arch/powerpc/mm/pgtable.c:304!
>>>>> cpu 0x0: Vector: 700 (Program Check) at [c000000c6d1e76c0]
>>>>>     pc: c00000000009a5ec: assert_pte_locked+0x14c/0x380
>>>>>     lr: c0000000005eeeec: pte_update+0x11c/0x190
>>>>>     sp: c000000c6d1e7950
>>>>>    msr: 8000000002029033
>>>>>   current = 0xc000000c6d172c80
>>>>>   paca    = 0xc000000003ba0000   irqmask: 0x03   irq_happened: 0x01
>>>>>     pid   = 1, comm = swapper/0
>>>>> kernel BUG at arch/powerpc/mm/pgtable.c:304!
>>>>> [link register   ] c0000000005eeeec pte_update+0x11c/0x190
>>>>> [c000000c6d1e7950] 0000000000000001 (unreliable)
>>>>> [c000000c6d1e79b0] c0000000005eee14 pte_update+0x44/0x190
>>>>> [c000000c6d1e7a10] c000000001a2ca9c pte_advanced_tests+0x160/0x3d8
>>>>> [c000000c6d1e7ab0] c000000001a2d4fc debug_vm_pgtable+0x7e8/0x1338
>>>>> [c000000c6d1e7ba0] c0000000000116ec do_one_initcall+0xac/0x5f0
>>>>> [c000000c6d1e7c80] c0000000019e4fac kernel_init_freeable+0x4dc/0x5a4
>>>>> [c000000c6d1e7db0] c000000000012474 kernel_init+0x24/0x160
>>>>> [c000000c6d1e7e20] c00000000000cbd0 ret_from_kernel_thread+0x5c/0x6c
>>>>>
>>>>> With DEBUG_VM disabled
>>>>>
>>>>> [   20.530152] BUG: Kernel NULL pointer dereference on read at 0x00000000
>>>>> [   20.530183] Faulting instruction address: 0xc0000000000df330
>>>>> cpu 0x33: Vector: 380 (Data SLB Access) at [c000000c6d19f700]
>>>>>     pc: c0000000000df330: memset+0x68/0x104
>>>>>     lr: c00000000009f6d8: hash__pmdp_huge_get_and_clear+0xe8/0x1b0
>>>>>     sp: c000000c6d19f990
>>>>>    msr: 8000000002009033
>>>>>    dar: 0
>>>>>   current = 0xc000000c6d177480
>>>>>   paca    = 0xc00000001ec4f400   irqmask: 0x03   irq_happened: 0x01
>>>>>     pid   = 1, comm = swapper/0
>>>>> [link register   ] c00000000009f6d8 hash__pmdp_huge_get_and_clear+0xe8/0x1b0
>>>>> [c000000c6d19f990] c00000000009f748 hash__pmdp_huge_get_and_clear+0x158/0x1b0 (unreliable)
>>>>> [c000000c6d19fa10] c0000000019ebf30 pmd_advanced_tests+0x1f0/0x378
>>>>> [c000000c6d19fab0] c0000000019ed088 debug_vm_pgtable+0x79c/0x1244
>>>>> [c000000c6d19fba0] c0000000000116ec do_one_initcall+0xac/0x5f0
>>>>> [c000000c6d19fc80] c0000000019a4fac kernel_init_freeable+0x4dc/0x5a4
>>>>> [c000000c6d19fdb0] c000000000012474 kernel_init+0x24/0x160
>>>>> [c000000c6d19fe20] c00000000000cbd0 ret_from_kernel_thread+0x5c/0x6c
>>>>>
>>>>> Changes from v3:
>>>>> * Address review feedback
>>>>> * Move page table depost and withdraw patch after adding pmdlock to avoid bisect failure.
>>>>
>>>> This version
>>>>
>>>> - Builds on x86, arm64, s390, arc, powerpc and riscv (defconfig with DEBUG_VM_PGTABLE)
>>>> - Runs on arm64 and x86 without any regression, atleast nothing that I have noticed
>>>> - Will be great if this could get tested on s390, arc, riscv, ppc32 platforms as well
>>>
>>> When I quickly tested v3, it worked fine, but now it turned out to
>>> only work fine "sometimes", both v3 and v4. I need to look into it
>>> further, but so far it seems related to the hugetlb_advanced_tests().
>>>
>>> I guess there was already some discussion on this test, but we did
>>> not receive all of the thread(s). Please always add at least
>>> linux-s390@vger.kernel.org and maybe myself and Vasily Gorbik <gor@linux.ibm.com>
>>> for further discussions.
>>
>> BTW, with myself I mean the new address gerald.schaefer@linux.ibm.com.
>> The old gerald.schaefer@de.ibm.com seems to work (again), but is not
>> very reliable.
>>
>> BTW2, a quick test with this change (so far) made the issues on s390
>> go away:
>>
>> @@ -1069,7 +1074,7 @@ static int __init debug_vm_pgtable(void)
>>         spin_unlock(ptl);
>>
>>  #ifndef CONFIG_PPC_BOOK3S_64
>> -       hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>> +       hugetlb_advanced_tests(mm, vma, (pte_t *) pmdp, pmd_aligned, vaddr, prot);
>>  #endif
>>
>>         spin_lock(&mm->page_table_lock);
>>
>> That would more match the "pte_t pointer" usage for hugetlb code,
>> i.e. just cast a pmd_t pointer to it. Also changed to pmd_aligned,
>> but I think the root cause is the pte_t pointer.
>>
>> Not entirely sure though if that would really be the correct fix.
>> I somehow lost whatever little track I had about what these tests
>> really want to check, and if that would still be valid with that
>> change.
> 
> Another potential issue, apparently not for s390, but maybe for
> others, is that the vaddr passed to hugetlb_advanced_tests() is
> also not pmd/pud size aligned, like you did in pmd/pud_advanced_tests().
> 
> I guess for the hugetlb_advanced_tests() you need to choose if
> you want to test pmd or pud hugepages, and accordingly prepare
> the *ptep, pfn and vaddr input. If you only check for CONFIG_HUGETLB_PAGE,
> then probably only pmd hugepages would be safe, there might be
> architectures only supporting one hugepage size.

I guess preparing for PMD based HugeTLB tests should be sufficient
for now, which can be improved later on to cover other levels.

> 
> So, for s390, at least the ptep input value is a problem. Still
> need to better understand how it goes wrong, but it seems to be
> fixed when using proper pmdp, and also works with pudp.
> 
> For others, especially the apparent issues on ppc64, the other
> non-hugepage aligned input pfn and vaddr might also be an issue,
> e.g. power at least seems to use the vaddr in its set_huge_pte_at()
> implementation for some pmd_off(mm, addr) calculation.
> 
> Again, sorry if this was already discussed, I missed most of it
> and honestly didn't properly look at the scarce mails that we did
> receive...

Sure, will consider these points and try improve tests afterwards.

  reply index

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-02 11:42 Aneesh Kumar K.V
2020-09-02 11:42 ` [PATCH v4 01/13] powerpc/mm: Add DEBUG_VM WARN for pmd_clear Aneesh Kumar K.V
2020-09-02 11:42 ` [PATCH v4 02/13] powerpc/mm: Move setting pte specific flags to pfn_pte Aneesh Kumar K.V
2020-09-02 12:30   ` Christophe Leroy
2020-09-02 11:42 ` [PATCH v4 03/13] mm/debug_vm_pgtable/ppc64: Avoid setting top bits in radom value Aneesh Kumar K.V
2020-09-04  4:03   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 04/13] mm/debug_vm_pgtables/hugevmap: Use the arch helper to identify huge vmap support Aneesh Kumar K.V
2020-09-02 12:40   ` Christophe Leroy
2020-09-02 12:53     ` Aneesh Kumar K.V
2020-09-04  4:08   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 05/13] mm/debug_vm_pgtable/savedwrite: Enable savedwrite test with CONFIG_NUMA_BALANCING Aneesh Kumar K.V
2020-09-04  4:09   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 06/13] mm/debug_vm_pgtable/THP: Mark the pte entry huge before using set_pmd/pud_at Aneesh Kumar K.V
2020-09-04  5:21   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry Aneesh Kumar K.V
2020-09-04  5:34   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 08/13] mm/debug_vm_pgtable/locks: Move non page table modifying test together Aneesh Kumar K.V
2020-09-04  3:58   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 09/13] mm/debug_vm_pgtable/locks: Take correct page table lock Aneesh Kumar K.V
2020-09-04  5:39   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 10/13] mm/debug_vm_pgtable/thp: Use page table depost/withdraw with THP Aneesh Kumar K.V
2020-09-04  4:21   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 11/13] mm/debug_vm_pgtable/pmd_clear: Don't use pmd/pud_clear on pte entries Aneesh Kumar K.V
2020-09-04  6:03   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 12/13] mm/debug_vm_pgtable/hugetlb: Disable hugetlb test on ppc64 Aneesh Kumar K.V
2020-09-04  6:19   ` Anshuman Khandual
2020-09-02 11:42 ` [PATCH v4 13/13] mm/debug_vm_pgtable: Avoid none pte in pte_clear_test Aneesh Kumar K.V
2020-09-11  2:13   ` Nathan Chancellor
2020-09-11  5:21     ` Aneesh Kumar K.V
2020-09-23  3:14       ` Anshuman Khandual
2020-10-11 20:02   ` Guenter Roeck
2020-10-12  4:29     ` Aneesh Kumar K.V
2020-09-02 11:46 ` Aneesh Kumar K.V
2020-09-04  4:16   ` Anshuman Khandual
2020-09-04  6:48 ` [PATCH v4 00/13] mm/debug_vm_pgtable fixes Anshuman Khandual
2020-09-04 15:26   ` Gerald Schaefer
2020-09-04 16:01     ` Gerald Schaefer
2020-09-04 17:53       ` Gerald Schaefer
2020-09-09  8:38         ` Anshuman Khandual [this message]
2020-09-08 15:39       ` Gerald Schaefer
2020-09-09  6:08         ` Aneesh Kumar K.V
2020-09-09 11:16           ` Gerald Schaefer
2020-09-09  8:15       ` Anshuman Khandual
2020-09-09 11:10         ` Gerald Schaefer
2020-09-09  8:08     ` Anshuman Khandual
2020-09-09 11:36       ` Gerald Schaefer
2020-09-13 11:03 ` [PATCH] mm/debug_vm_pgtable: Avoid doing memory allocation with pgtable_t mapped Aneesh Kumar K.V
2020-09-13 13:42   ` Matthew Wilcox
2020-10-13 20:58 ` [PATCH v4 00/13] mm/debug_vm_pgtable fixes Andrew Morton
2020-10-14  3:15   ` Aneesh Kumar K.V
2020-10-14 20:36     ` Andrew Morton
2020-10-15  2:59       ` Anshuman Khandual

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