On Wed, Mar 30, 2022 at 12:42 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> I started testing new patches and it crashed when doing the x86-32 test on
> boot up.
>
> Initializing HighMem for node 0 (000375fe:0021ee00)
> BUG: kernel NULL pointer dereference, address: 00000878
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> *pdpt = 0000000000000000 *pde = f0000000f000eef3
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.17.0-test+ #469
> Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
> EIP: get_pfnblock_flags_mask+0x2c/0x36
> Code: 6d ea ff 55 89 e5 56 89 ce 53 8b 18 89 d8 c1 eb 1e e8 f7 fb ff ff 69 db c0 02 00 00 89 c1 89 c2 c1 ea 05 8b 83 7c d7 79 c1 5b <8b> 04 90 d3 e8 21 f0 5e 5d c3 55 89 e5 57 56 89 d6 53 89 c3 64 a1
The whole function is in that Code: thing, and it decodes to:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 56 push %esi
4: 89 ce mov %ecx,%esi
6: 53 push %ebx
7: 8b 18 mov (%eax),%ebx
9: 89 d8 mov %ebx,%eax
b: c1 eb 1e shr $0x1e,%ebx
e: e8 f7 fb ff ff call 0xfffffc0a
13: 69 db c0 02 00 00 imul $0x2c0,%ebx,%ebx
19: 89 c1 mov %eax,%ecx
1b: 89 c2 mov %eax,%edx
1d: c1 ea 05 shr $0x5,%edx
20: 8b 83 7c d7 79 c1 mov -0x3e862884(%ebx),%eax
26: 5b pop %ebx
27:* 8b 04 90 mov (%eax,%edx,4),%eax <-- trapping instruction
2a: d3 e8 shr %cl,%eax
2c: 21 f0 and %esi,%eax
2e: 5e pop %esi
2f: 5d pop %ebp
30: c3 ret
with '%eax' being NULL, and %edx being 0x21e.
(The call seems to be to 'pfn_to_bitidx().isra.0' if my compiler does
similar code generation, so it's out-of-lined part of pfn_to_bitidx()
despite being marked inline)
So that oops is that
word = bitmap[word_bitidx];
line, with 'bitmap' being NULL (and %edx contains 'word_bitidx').
Looking around, your 'config-bad' doesn't even have
CONFIG_MEMORY_ISOLATION enabled, and so I suspect the culprit is this
part of the change:
- if (unlikely(has_isolate_pageblock(zone))) {
which used to always be false for that config, and now the code is
suddenly enabled.
Alternatively, that code just can't deal with highmem properly.
But I didn't really analyze things, I'm mainly doing pattern matching here.
Zi Yan - and all the people who ack'ed and reviewed this - please take
a deeper look..
Linus
