Re: [PATCH v4 00/13] mm/debug_vm_pgtable fixes
From: Anshuman Khandual <hidden>
Date: 2020-09-09 08:16:26
Also in:
linux-mm, linux-riscv, linux-s390
On 09/04/2020 09:31 PM, Gerald Schaefer wrote:
On Fri, 4 Sep 2020 17:26:47 +0200 Gerald Schaefer [off-list ref] wrote:quoted
On Fri, 4 Sep 2020 12:18:05 +0530 Anshuman Khandual [off-list ref] wrote:quoted
On 09/02/2020 05:12 PM, Aneesh Kumar K.V wrote:quoted
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 wellWhen 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 [off-list ref] 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.
Sure, noted.
quoted hunk ↗ jump to hunk
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.
Ideally, the pte_t pointer used here should be from huge_pte_alloc() not from pte_alloc_map_lock() as the case currently.
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.