Re: WARNING in get_pat_info

[David Hildenbrand]

On 16.08.24 11:44, lee bruce wrote:
> Hello, I found a bug titled "WARNING in get_pat_info" with modified
> syzkaller in the lasted upstream and lasted mm branches.

Below report is from 6.10.0, which is not precisely "latest upstream", 
but I assume you have similar reports on upstream?

commit 04c35ab3bdae7fefbd7c7a7355f29fa03a035221
Author: David Hildenbrand <david@xxxxxxxxxx>
Date:   Wed Apr 3 23:21:30 2024 +0200

    x86/mm/pat: fix VM_PAT handling in COW mappings

Was part of v6.9, but this is a different issue.

> If you fix this issue, please add the following tag to the commit:
> Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
> Reported-by: yuxin wang <wang1315768607@xxxxxxx>
>
> TITLE: WARNING in get_pat_info
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 12458 at arch/x86/mm/pat/memtype.c:1002
> get_pat_info+0x4b6/0x5c0 arch/x86/mm/pat/memtype.c:1002

This is the WARN_ON_ONCE(1) in get_pat_info(). We don't find any page in 
the mapping, so it vanished already.

I thought we discovered that already recently and discussed it here:

https://lore.kernel.org/all/20240712144244.3090089-1-peterx@xxxxxxxxxx/T/#u

Which was supposed to fix this problem IIRC.

That patch result in other issues, and my analysis about them is here:

https://lore.kernel.org/all/8da2b3bf-b9bf-44e3-88ff-750dc91c2388@xxxxxxxxxx/

We didn't have a report from an in-tree driver, so we decided to "not 
care" about these reports:

https://lore.kernel.org/all/116ca902-103d-47cb-baf0-905983baf9bb@xxxxxxxxxx/


But I don't see Peter's patch upstream.

Peter, do you recall what the conclusion on that was?


--
Cheers,

David / dhildenb