[PATCH v3 09/13] mm/debug_vm_pgtable/locks: Move non page table modifying test together

Tue Sep 1 19:33:23 AEST 2020

On 09/01/2020 12:08 PM, Aneesh Kumar K.V wrote:
> On 9/1/20 9:11 AM, Anshuman Khandual wrote:
>>
>>
>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>>> This will help in adding proper locks in a later patch
>>
>> It really makes sense to classify these tests here as static and dynamic.
>> Static are the ones that test via page table entry values modification
>> without changing anything on the actual page table itself. Where as the
>> dynamic tests do change the page table. Static tests would probably never
>> require any lock synchronization but the dynamic ones will do.
>>
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>>> ---
>>>   mm/debug_vm_pgtable.c | 52 ++++++++++++++++++++++++-------------------
>>>   1 file changed, 29 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>> index 0ce5c6a24c5b..78c8af3445ac 100644
>>> --- a/mm/debug_vm_pgtable.c
>>> +++ b/mm/debug_vm_pgtable.c
>>> @@ -992,7 +992,7 @@ static int __init debug_vm_pgtable(void)
>>>       p4dp = p4d_alloc(mm, pgdp, vaddr);
>>>       pudp = pud_alloc(mm, p4dp, vaddr);
>>>       pmdp = pmd_alloc(mm, pudp, vaddr);
>>> -    ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>> +    ptep = pte_alloc_map(mm, pmdp, vaddr);
>>>         /*
>>>        * Save all the page table page addresses as the page table
>>> @@ -1012,33 +1012,12 @@ static int __init debug_vm_pgtable(void)
>>>       p4d_basic_tests(p4d_aligned, prot);
>>>       pgd_basic_tests(pgd_aligned, prot);
>>>   -    pte_clear_tests(mm, ptep, vaddr);
>>> -    pmd_clear_tests(mm, pmdp);
>>> -    pud_clear_tests(mm, pudp);
>>> -    p4d_clear_tests(mm, p4dp);
>>> -    pgd_clear_tests(mm, pgdp);
>>> -
>>> -    pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>> -    pmd_advanced_tests(mm, vma, pmdp, pmd_aligned, vaddr, prot, saved_ptep);
>>> -    pud_advanced_tests(mm, vma, pudp, pud_aligned, vaddr, prot);
>>> -    hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>> -
>>>       pmd_leaf_tests(pmd_aligned, prot);
>>>       pud_leaf_tests(pud_aligned, prot);
>>>   -    pmd_huge_tests(pmdp, pmd_aligned, prot);
>>> -    pud_huge_tests(pudp, pud_aligned, prot);
>>> -
>>>       pte_savedwrite_tests(pte_aligned, protnone);
>>>       pmd_savedwrite_tests(pmd_aligned, protnone);
>>>   -    pte_unmap_unlock(ptep, ptl);
>>> -
>>> -    pmd_populate_tests(mm, pmdp, saved_ptep);
>>> -    pud_populate_tests(mm, pudp, saved_pmdp);
>>> -    p4d_populate_tests(mm, p4dp, saved_pudp);
>>> -    pgd_populate_tests(mm, pgdp, saved_p4dp);
>>> -
>>>       pte_special_tests(pte_aligned, prot);
>>>       pte_protnone_tests(pte_aligned, protnone);
>>>       pmd_protnone_tests(pmd_aligned, protnone);
>>> @@ -1056,11 +1035,38 @@ static int __init debug_vm_pgtable(void)
>>>       pmd_swap_tests(pmd_aligned, prot);
>>>         swap_migration_tests();
>>> -    hugetlb_basic_tests(pte_aligned, prot);
>>>         pmd_thp_tests(pmd_aligned, prot);
>>>       pud_thp_tests(pud_aligned, prot);
>>>   +    /*
>>> +     * Page table modifying tests
>>> +     */
>>
>> In this comment, please do add some more details about how these tests
>> need proper locking mechanism unlike the previous static ones. Also add
>> a similar comment section for the static tests that dont really change
>> page table and need not require corresponding locking mechanism. Both
>> comment sections will make this classification clear.
>>
>>> +    pte_clear_tests(mm, ptep, vaddr);
>>> +    pmd_clear_tests(mm, pmdp);
>>> +    pud_clear_tests(mm, pudp);
>>> +    p4d_clear_tests(mm, p4dp);
>>> +    pgd_clear_tests(mm, pgdp);
>>> +
>>> +    ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>> +    pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>> +    pmd_advanced_tests(mm, vma, pmdp, pmd_aligned, vaddr, prot, saved_ptep);
>>> +    pud_advanced_tests(mm, vma, pudp, pud_aligned, vaddr, prot);
>>> +    hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>> +
>>> +
>>> +    pmd_huge_tests(pmdp, pmd_aligned, prot);
>>> +    pud_huge_tests(pudp, pud_aligned, prot);
>>> +
>>> +    pte_unmap_unlock(ptep, ptl);
>>> +
>>> +    pmd_populate_tests(mm, pmdp, saved_ptep);
>>> +    pud_populate_tests(mm, pudp, saved_pmdp);
>>> +    p4d_populate_tests(mm, p4dp, saved_pudp);
>>> +    pgd_populate_tests(mm, pgdp, saved_p4dp);
>>> +
>>> +    hugetlb_basic_tests(pte_aligned, prot);
>>
>> hugetlb_basic_tests() is a non page table modifying static test and
>> should be classified accordingly.
>>
>>> +
>>>       p4d_free(mm, saved_p4dp);
>>>       pud_free(mm, saved_pudp);
>>>       pmd_free(mm, saved_pmdp);
>>>
>>
>> Changes till this patch fails to boot on arm64 platform. This should be
>> folded with the next patch.
>>
>> [   17.080644] ------------[ cut here ]------------
>> [   17.081342] kernel BUG at mm/pgtable-generic.c:164!
>> [   17.082091] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>> [   17.082977] Modules linked in:
>> [   17.083481] CPU: 79 PID: 1 Comm: swapper/0 Tainted: G        W         5.9.0-rc2-00105-g740e72cd6717 #14
>> [   17.084998] Hardware name: linux,dummy-virt (DT)
>> [   17.085745] pstate: 60400005 (nZCv daif +PAN -UAO BTYPE=--)
>> [   17.086645] pc : pgtable_trans_huge_deposit+0x58/0x60
>> [   17.087462] lr : debug_vm_pgtable+0x4dc/0x8f0
>> [   17.088168] sp : ffff80001219bcf0
>> [   17.088710] x29: ffff80001219bcf0 x28: ffff8000114ac000
>> [   17.089574] x27: ffff8000114ac000 x26: 0020000000000fd3
>> [   17.090431] x25: 0020000081400fd3 x24: fffffe00175c12c0
>> [   17.091286] x23: ffff0005df04d1a8 x22: 0000f18d6e035000
>> [   17.092143] x21: ffff0005dd790000 x20: ffff0005df18e1a8
>> [   17.093003] x19: ffff0005df04cb80 x18: 0000000000000014
>> [   17.093859] x17: 00000000b76667d0 x16: 00000000fd4e6611
>> [   17.094716] x15: 0000000000000001 x14: 0000000000000002
>> [   17.095572] x13: 000000000055d966 x12: fffffe001755e400
>> [   17.096429] x11: 0000000000000008 x10: ffff0005fcb6e210
>> [   17.097292] x9 : ffff0005fcb6e210 x8 : 0020000081590fd3
>> [   17.098149] x7 : ffff0005dd71e0c0 x6 : ffff0005df18e1a8
>> [   17.099006] x5 : 0020000081590fd3 x4 : 0020000081590fd3
>> [   17.099862] x3 : ffff0005df18e1a8 x2 : fffffe00175c12c0
>> [   17.100718] x1 : fffffe00175c1300 x0 : 0000000000000000
>> [   17.101583] Call trace:
>> [   17.101993]  pgtable_trans_huge_deposit+0x58/0x60
>> [   17.102754]  do_one_initcall+0x74/0x1cc
>> [   17.103381]  kernel_init_freeable+0x1d0/0x238
>> [   17.104089]  kernel_init+0x14/0x118
>> [   17.104658]  ret_from_fork+0x10/0x34
>> [   17.105251] Code: f9000443 f9000843 f9000822 d65f03c0 (d4210000)
>> [   17.106303] ---[ end trace e63471e00f8c147f ]---
>>
> 
> IIUC, this should happen even without the series right? This is
> 
>     assert_spin_locked(pmd_lockptr(mm, pmdp));

Crash does not happen without this series. A previous patch [PATCH v3 08/13]
added pgtable_trans_huge_deposit/withdraw() in pmd_advanced_tests(). arm64
does not define __HAVE_ARCH_PGTABLE_DEPOSIT and hence falls back on generic
pgtable_trans_huge_deposit() which the asserts the lock.