Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers

Qian Cai
2020-03-04T01:39:47Z

> Below is slightly modified version of your change above and should still
> prevent the bug on powerpc. Will it be possible for you to re-test this
> ? Once confirmed, will send a patch enabling this test on powerpc64
> keeping your authorship. Thank you.

This works fine on radix MMU but I decided to go a bit future to test hash
MMU. The kernel will stuck here below. I did confirm that pte_alloc_map_lock()
was successful, so I don’t understand hash MMU well enough to tell why
it could still take an interrupt at pte_clear_tests() even before we calls
pte_unmap_unlock()?

[ 33.881515][ T1] ok 8 - property-entry
[ 33.883653][ T1] debug_vm_pgtable: debug_vm_pgtable: Validating
architecture page table helpers
[ 60.418885][ C8] watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
[swapper/0:1]
[ 60.418913][ C8] Modules linked in:
[ 60.418927][ C8] irq event stamp: 2896762
[ 60.418945][ C8] hardirqs last enabled at (2896761): [<c00000000000dec8>]
fast_exc_return_irq+0x28/0x34
[ 60.418960][ C8] hardirqs last disabled at (2896762): [<c00000000000924c>]
decrementer_common+0x10c/0x130
[ 60.418985][ C8] softirqs last enabled at (2896760): [<c0000000009a1bf0>]
__do_softirq+0x640/0x8c8
[ 60.419009][ C8] softirqs last disabled at (2896753): [<c000000000113cbc>]
irq_exit+0x16c/0x1d0
[ 60.419024][ C8] CPU: 8 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-
20200303+ #7
[ 60.419055][ C8] NIP: c00000000103dc14 LR: c00000000103db0c CTR:
0000000000000000
[ 60.419076][ C8] REGS: c00000003dd4fa30 TRAP: 0901 Not tainted (5.6.0-
rc4-next-20200303+)
[ 60.419107][ C8] MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE> CR:
42000222 XER: 00000000
[ 60.419134][ C8] CFAR: c00000000103dc1c IRQMASK: 0
[ 60.419134][ C8] GPR00: c00000000103db0c c00000003dd4fcc0 c000000001657d00
05210001000000c0
[ 60.419134][ C8] GPR04: 8000000000000105 000000000000000a 00000000f4d9864c
0000000000000001
[ 60.419134][ C8] GPR08: 0000000000000000 ffffffffffffffff 0000000000000001
00000000000a0000
[ 60.419134][ C8] GPR12: 0000000000000000 c000001fffff9880
[ 60.419220][ C8] NIP [c00000000103dc14] debug_vm_pgtable+0x7a8/0xbb4
hash__pte_update at arch/powerpc/include/asm/book3s/64/hash.h:159
(inlined by) pte_update at arch/powerpc/include/asm/book3s/64/pgtable.h:359
(inlined by) pte_clear at arch/powerpc/include/asm/book3s/64/pgtable.h:477
(inlined by) pte_clear_tests at mm/debug_vm_pgtable.c:259
(inlined by) debug_vm_pgtable at mm/debug_vm_pgtable.c:368
[ 60.419241][ C8] LR [c00000000103db0c] debug_vm_pgtable+0x6a0/0xbb4
pmd_basic_tests at mm/debug_vm_pgtable.c:74
(inlined by) debug_vm_pgtable at mm/debug_vm_pgtable.c:363
[ 60.419260][ C8] Call Trace:
[ 60.419278][ C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[ 60.419302][ C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[ 60.419325][ C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[ 60.419363][ C8] Instruction dump:
[ 60.419382][ C8] 7d075078 7ce74b78 7ce0f9ad 40c2fff0 7e449378 7fc3f378
4b03531d 60000000
[ 60.419416][ C8] 48000080 3920ffff 39400001 39000000 <7e00f8a8> 7e075039
40c2fff8 7e074878
[ 98.908889][ C8] rcu: INFO: rcu_sched self-detected stall on CPU
[ 98.908933][ C8] rcu: 8-....: (6500 ticks this GP)
idle=522/1/0x4000000000000002 softirq=132/132 fqs=3250
[ 98.908963][ C8] (t=6501 jiffies g=-719 q=510)
[ 98.908984][ C8] NMI backtrace for cpu 8
[ 98.909012][ C8] CPU: 8 PID: 1 Comm: swapper/0 Tainted:
G L 5.6.0-rc4-next-20200303+ #7
[ 98.909025][ C8] Call Trace:
[ 98.909046][ C8] [c00000003dd4f360] [c000000000970fe0]
dump_stack+0xf4/0x164 (unreliable)
[ 98.909070][ C8] [c00000003dd4f3b0] [c00000000097dcf4]
nmi_cpu_backtrace+0x1b4/0x1e0
[ 98.909084][ C8] [c00000003dd4f450] [c00000000097df48]
nmi_trigger_cpumask_backtrace+0x228/0x2c0
[ 98.909118][ C8] [c00000003dd4f500] [c000000000057bf8]
arch_trigger_cpumask_backtrace+0x28/0x40
[ 98.909152][ C8] [c00000003dd4f520] [c000000000202dd4]
rcu_dump_cpu_stacks+0x1c4/0x234
[ 98.909184][ C8] [c00000003dd4f5a0] [c000000000201634]
rcu_sched_clock_irq+0xd54/0x1130
[ 98.909207][ C8] [c00000003dd4f6c0] [c000000000217068]
update_process_times+0x48/0xb0
[ 98.909239][ C8] [c00000003dd4f6f0] [c0000000002358b4]
tick_sched_handle+0x34/0xb0
[ 98.909262][ C8] [c00000003dd4f720] [c0000000002361d8]
tick_sched_timer+0x68/0xe0
[ 98.909284][ C8] [c00000003dd4f760] [c000000000219768]
__hrtimer_run_queues+0x528/0xa60
[ 98.909306][ C8] [c00000003dd4f880] [c00000000021ab58]
hrtimer_interrupt+0x128/0x330
[ 98.909329][ C8] [c00000003dd4f930] [c00000000002e1b4]
timer_interrupt+0x264/0x680
[ 98.909352][ C8] [c00000003dd4f9c0] [c000000000009264]
decrementer_common+0x124/0x130
[ 98.909366][ C8] --- interrupt: 901 at debug_vm_pgtable+0x7a8/0xbb4
[ 98.909366][ C8] LR = debug_vm_pgtable+0x6a0/0xbb4
[ 98.909402][ C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[ 98.909435][ C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[ 98.909467][ C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[ 124.418885][ C8] watchdog: BUG: soft lockup - CPU#8 stuck for 22s!
[swapper/0:1]
[ 124.418914][ C8] Modules linked in:
[ 124.418926][ C8] irq event stamp: 2937938
[ 124.418940][ C8] hardirqs last enabled at (2937937): [<c00000000000dec8>]
fast_exc_return_irq+0x28/0x34
[ 124.418964][ C8] hardirqs last disabled at (2937938): [<c00000000000924c>]
decrementer_common+0x10c/0x130
[ 124.418980][ C8] softirqs last enabled at (2937936): [<c0000000009a1bf0>]
__do_softirq+0x640/0x8c8
[ 124.419013][ C8] softirqs last disabled at (2937929): [<c000000000113cbc>]
irq_exit+0x16c/0x1d0
[ 124.419036][ C8] CPU: 8 PID: 1 Comm: swapper/0 Tainted:
G L 5.6.0-rc4-next-20200303+ #7
[ 124.419059][ C8] NIP: c00000000103dc14 LR: c00000000103db0c CTR:
0000000000000000
[ 124.419080][ C8] REGS: c00000003dd4fa30 TRAP: 0901 Tainted:
G L (5.6.0-rc4-next-20200303+)
[ 124.419103][ C8] MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE> CR:
42000222 XER: 00000000
[ 124.419121][ C8] CFAR: c00000000103dc1c IRQMASK: 0
[ 124.419121][ C8] GPR00: c00000000103db0c c00000003dd4fcc0 c000000001657d00
05210001000000c0
[ 124.419121][ C8] GPR04: 8000000000000105 000000000000000a 00000000f4d9864c
0000000000000001
[ 124.419121][ C8] GPR08: 0000000000000000 ffffffffffffffff 0000000000000001
00000000000a0000
[ 124.419121][ C8] GPR12: 0000000000000000 c000001fffff9880
[ 124.419234][ C8] NIP [c00000000103dc14] debug_vm_pgtable+0x7a8/0xbb4
[ 124.419254][ C8] LR [c00000000103db0c] debug_vm_pgtable+0x6a0/0xbb4
[ 124.419274][ C8] Call Trace:
[ 124.419291][ C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[ 124.419324][ C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[ 124.419347][ C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[ 124.419359][ C8] Instruction dump:
[ 124.419378][ C8] 7d075078 7ce74b78 7ce0f9ad 40c2fff0 7e449378 7fc3f378
4b03531d 60000000
[ 124.419412][ C8] 48000080 3920ffff 39400001 39000000 <7e00f8a8> 7e075039
40c2fff8 7e074878

>
> mm/debug_vm_pgtable.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 96dd7d574cef..c310f52c2b80 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -250,13 +250,14 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> }
> #endif
>
> -static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
> +static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
> + unsigned long vaddr)
> {
> pte_t pte = READ_ONCE(*ptep);
>
> pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> WRITE_ONCE(*ptep, pte);
> - pte_clear(mm, 0, ptep);
> + pte_clear(mm, vaddr, ptep);
> pte = READ_ONCE(*ptep);
> WARN_ON(!pte_none(pte));
> }
> @@ -302,6 +303,7 @@ static unsigned long __init get_random_vaddr(void)
> void __init debug_vm_pgtable(void)
> {
> struct mm_struct *mm;
> + spinlock_t *uninitialized_var(ptl);
> pgd_t *pgdp;
> p4d_t *p4dp, *saved_p4dp;
> pud_t *pudp, *saved_pudp;
> @@ -344,7 +346,7 @@ void __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(mm, pmdp, vaddr);
> + ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>
> /*
> * Save all the page table page addresses as the page table
> @@ -364,13 +366,13 @@ void __init debug_vm_pgtable(void)
> p4d_basic_tests(p4d_aligned, prot);
> pgd_basic_tests(pgd_aligned, prot);
>
> - pte_clear_tests(mm, ptep);
> + 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_unmap(ptep);
> + pte_unmap_unlock(ptep, ptl);
>
> pmd_populate_tests(mm, pmdp, saved_ptep);
> pud_populate_tests(mm, pudp, saved_pmdp);
> --
> 2.20.1