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

[Qian Cai <cai@lca.pw>]

> 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