Re: [PATCH -mm] mm,numa,mprotect: always continue after finding a stable thp page

[Sasha Levin]

On 03/11/2014 02:06 PM, Mel Gorman wrote:
> On Tue, Mar 11, 2014 at 01:33:00PM -0400, Sasha Levin wrote:
> > Okay. So just this patch on top of the latest -next shows the following issues:
> >
> > 1. BUG in task_numa_work:
> >
> > [  439.417171] BUG: unable to handle kernel paging request at ffff880e17530c00
> > [  439.418216] IP: [<ffffffff81299385>] vmacache_find+0x75/0xa0
> > [  439.419073] PGD 8904067 PUD 1028fcb067 PMD 1028f10067 PTE 8000000e17530060
> > [  439.420340] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> > [  439.420340] Dumping ftrace buffer:
> > [  439.420340]    (ftrace buffer empty)
> > [  439.420340] Modules linked in:
> > [  439.420340] CPU: 12 PID: 9937 Comm: trinity-c212 Tainted: G        W    3.14.0-rc5-next-20140307-sasha-00009-g3b24300-dirty #137
> > [  439.420340] task: ffff880e1a45b000 ti: ffff880e1a490000 task.ti: ffff880e1a490000
> > [  439.420340] RIP: 0010:[<ffffffff81299385>]  [<ffffffff81299385>] vmacache_find+0x75/0xa0
> > [  439.420340] RSP: 0018:ffff880e1a491e68  EFLAGS: 00010286
> > [  439.420340] RAX: ffff880e17530c00 RBX: 0000000000000000 RCX: 0000000000000001
> > [  439.420340] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff880e1a45b000
> > [  439.420340] RBP: ffff880e1a491e68 R08: 0000000000000000 R09: 0000000000000000
> > [  439.420340] R10: 0000000000000001 R11: 0000000000000000 R12: ffff880e1ab75000
> > [  439.420340] R13: ffff880e1ab75000 R14: 0000000000010000 R15: 0000000000000000
> > [  439.420340] FS:  00007f3458c05700(0000) GS:ffff880d2b800000(0000) knlGS:0000000000000000
> > [  439.420340] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [  439.420340] CR2: ffff880e17530c00 CR3: 0000000e1a472000 CR4: 00000000000006a0
> > [  439.420340] Stack:
> > [  439.420340]  ffff880e1a491e98 ffffffff812a7610 ffffffff8118de40 0000000000000117
> > [  439.420340]  00000001000036da ffff880e1a45b000 ffff880e1a491ef8 ffffffff8118de4b
> > [  439.420340]  ffff880e1a491ec8 ffffffff81269575 ffff880e1ab750a8 ffff880e1a45b000
> > [  439.420340] Call Trace:
> > [  439.420340]  [<ffffffff812a7610>] find_vma+0x20/0x90
> > [  439.420340]  [<ffffffff8118de40>] ? task_numa_work+0x130/0x360
> > [  439.420340]  [<ffffffff8118de4b>] task_numa_work+0x13b/0x360
> > [  439.420340]  [<ffffffff81269575>] ? context_tracking_user_exit+0x195/0x1d0
> > [  439.420340]  [<ffffffff8116c5be>] task_work_run+0xae/0xf0
> > [  439.420340]  [<ffffffff8106ffbe>] do_notify_resume+0x8e/0xe0
> > [  439.420340]  [<ffffffff844b17a2>] int_signal+0x12/0x17
> > [  439.420340] Code: 42 10 00 00 00 00 48 c7 42 18 00 00 00 00 eb 38 66 0f 1f 44 00 00 31 d2 48 89 c7 48 63 ca 48 8b 84 cf b8 07 00 00 48 85 c0 74 0b <48> 39 30 77 06 48 3b 70 08 72 12 ff c2 83 fa 04 75 de 66 0f 1f
> > [  439.420340] RIP  [<ffffffff81299385>] vmacache_find+0x75/0xa0
> > [  439.420340]  RSP <ffff880e1a491e68>
> > [  439.420340] CR2: ffff880e17530c00
>
> Ok, this does not look related. It looks like damage from the VMA caching
> patches, possibly a use-after free. I'm skeptical that it's related to
> automatic NUMA balancing as such based on the second trace you posted.

It's a bit weird because right after applying the patch I've hit this trace twice while
never seeing it previously.

But it's very possible since there are quite a lot of different mm issues around right now.

> What does addr2line -e vmlinux ffffffff81299385 say? I want to be sure
> it looks like a vma dereference without risking making a mistake
> decoding it.

mm/vmacache.c:75

Or:

	if (vma && vma->vm_start <= addr && vma->vm_end > addr)

> 1. Does this bug trigger even if automatic NUMA balancing is disabled?

(assuming we're talking about kernel BUG at mm/mmap.c:439!)

Yes, same result with numa_balancing=disable.

> 2. Does this bug trigger if DEBUG_PAGEALLOC is disabled? If it's a
> 	use-after free then the bug would still be there.

Still there.

> 3. Can you test with the following patches reverted please?
>
> 	e15d25d9c827b4346a36a3a78dd566d5ad353402 mm-per-thread-vma-caching-fix-fix
> 	e440e20dc76803cdab616b4756c201d5c72857f2 mm-per-thread-vma-caching-fix
> 	0d9ad4220e6d73f63a9eeeaac031b92838f75bb3 mm: per-thread vma caching
>
> The last patch will not revert cleanly (least it didn't for me) but it
> was just a case of git rm the two affected files, remove any include of
> vmacache.h and commit the rest.

Don't see the issues I've reported before now.



Thanks,
Sasha
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