linux-kernel - Re: [RFC] mm/migrate: make sure folio_unlock() before folio_wait

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Message-ID: <20251013043631.GC6925@system.software.com>
Date: Mon, 13 Oct 2025 13:36:31 +0900
From: Byungchul Park <byungchul@...com>
To: David Hildenbrand <david@...hat.com>
Cc: Yunseong Kim <ysk@...lloc.com>, Hillf Danton <hdanton@...a.com>,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel_team@...ynix.com,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: Re: [RFC] mm/migrate: make sure folio_unlock() before
 folio_wait_writeback()

On Tue, Oct 07, 2025 at 09:04:59AM +0200, David Hildenbrand wrote:
> On 07.10.25 08:32, Yunseong Kim wrote:
> > Hi Hillf,
> > 
> > Here are the syzlang and kernel log, and you can also find the gist snippet
> > in the body of the first RFC mail:
> > 
> >   https://gist.github.com/kzall0c/a6091bb2fd536865ca9aabfd017a1fc5
> > 
> > I am reviewing this issue again on the v6.17, The issue is always reproducible,
> > usually occurring within about 10k attempts with the 8 procs.
> 
> I can see a DEPT splat and I wonder what happens if DEPT is disabled.
> 
> Will the machine actually deadlock or is this just DEPT complaining (and

Of course, it was an actual deadlock, not just DEPT splat.

However, even though this patch resolved the acutal hang issue, it
looked mismatched between the watchdog hang report and the DEPT report.
We are now re-checking it using the reproducer.

	Byungchul

> probably getting something wrong)?
> 
> --
> Cheers
> 
> David / dhildenb