Subject: Re: [PATCH V6 0/2] mm/debug: Add tests validating architecture page table helpers

From: Qian Cai <[email-masked]>
Date: Tue, 15 Oct 2019 14:42:00 -0400

On Tue, 2019-10-15 at 20:51 +0530, Anshuman Khandual wrote:
> 
> On 10/15/2019 08:11 PM, Qian Cai wrote:
> > The x86 will crash with linux-next during boot due to this series (v5) with the
> > config below plus CONFIG_DEBUG_VM_PGTABLE=y. I am not sure if v6 would address
> > it.
> > 
> > https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
> > 
> > [   33.862600][    T1] page:ffffea0009000000 is uninitialized and poisoned
> > [   33.862608][    T1] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > ffffff871140][    T1]  ? _raw_spin_unlock_irq+0x27/0x40
> > [   33.871140][    T1]  ? rest_init+0x307/0x307
> > [   33.871140][    T1]  kernel_init+0x11/0x139
> > [   33.871140][    T1]  ? rest_init+0x307/0x307
> > [   33.871140][    T1]  ret_from_fork+0x27/0x50
> > [   33.871140][    T1] Modules linked in:
> > [   33.871140][    T1] ---[ end trace e99d392b0f7befbd ]---
> > [   33.871140][    T1] RIP: 0010:alloc_gigantic_page_order+0x3fe/0x490
> 
> Hmm, with defconfig (DEBUG_VM=y and DEBUG_VM_PGTABLE=y) it does not crash but
> with the config above, it does. Just wondering if it is possible that these
> pages might not been initialized yet because DEFERRED_STRUCT_PAGE_INIT=y ?

Yes, this patch works fine.

diff --git a/init/main.c b/init/main.c
index 676d8020dd29..591be8f9e8e0 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1177,7 +1177,6 @@ static noinline void __init kernel_init_freeable(void)
        workqueue_init();
 
        init_mm_internals();
-       debug_vm_pgtable();
 
        do_pre_smp_initcalls();
        lockup_detector_init();
@@ -1186,6 +1185,8 @@ static noinline void __init kernel_init_freeable(void)
        sched_init_smp();
 
        page_alloc_init_late();
+       debug_vm_pgtable();
+
        /* Initialize page ext after all struct pages are initialized. */
        page_ext_init();

> 
> [   13.898549][    T1] page:ffffea0005000000 is uninitialized and poisoned
> [   13.898549][    T1] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> [   13.898549][    T1] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> [   13.898549][    T1] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> [   13.898549][    T1] ------------[ cut here ]------------
> [   13.898549][    T1] kernel BUG at ./include/linux/mm.h:1107!
> [   13.898549][    T1] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
> [   13.898549][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc3-next-20191015+ #

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