linux-kernel - Re: WARNING in get_pat

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Message-ID: <9babc9ff-00f0-44c7-a2fe-8aeadfefe75a@redhat.com>
Date: Thu, 17 Oct 2024 21:27:35 +0200
From: David Hildenbrand <david@...hat.com>
To: lee bruce <xrivendell7@...il.com>, dave.hansen@...ux.intel.com,
 linux-kernel@...r.kernel.org, luto@...nel.org, peterz@...radead.org
Cc: bp@...en8.de, hpa@...or.com, mingo@...hat.com,
 Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
 wang1315768607@....com, syzkaller@...glegroups.com,
 Peter Xu <peterx@...hat.com>
Subject: Re: WARNING in get_pat_info

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@...hat.com>
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@...il.com>
> Reported-by: yuxin wang <wang1315768607@....com>
> 
> 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@redhat.com/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@redhat.com/

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@redhat.com/

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

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

-- 
Cheers,

David / dhildenb