linux-kernel - Re: [PATCHv2 2/2] mm/truncate: Unmap large folio on split failure

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Message-ID: <c519f6f8-37ca-4016-b8f3-aef9b9bda9c7@redhat.com>
Date: Mon, 27 Oct 2025 11:38:37 +0100
From: David Hildenbrand <david@...hat.com>
To: Hugh Dickins <hughd@...gle.com>, Kiryl Shutsemau <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>,
 Johannes Weiner <hannes@...xchg.org>, Shakeel Butt <shakeel.butt@...ux.dev>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Darrick J. Wong" <djwong@...nel.org>, Dave Chinner <david@...morbit.com>,
 linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, Kiryl Shutsemau <kas@...nel.org>
Subject: Re: [PATCHv2 2/2] mm/truncate: Unmap large folio on split failure

> 
> And a final nit: I'd delete that WARN_ON(folio_mapped(folio)) myself,
> all it could ever achieve is perhaps a very rare syzbot report which
> nobody would want to spend time on.

I think that's the crucial part: what are we supposed to do if both 
splitting and unmapping fails? Silently violate SIGBUS semantics like we 
did before this patch?

So far our understanding was that for file pages, unmapping should not 
fail, but I am not 100% sure if that's really the case.

-- 
Cheers

David / dhildenb