linux-kernel - Re: [PATCH v3 04/15] mm, swap: check page poison flag after locking it

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Message-ID: <CAKEwX=ONB=z3h5VdgoyXj=2PZ1Qpzi9zVzGioGstepHie7i+_A@mail.gmail.com>
Date: Fri, 12 Sep 2025 10:17:48 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Kairui Song <ryncsn@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>, 
	Barry Song <baohua@...nel.org>, Baoquan He <bhe@...hat.com>, 
	Kemeng Shi <shikemeng@...weicloud.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Ying Huang <ying.huang@...ux.alibaba.com>, Johannes Weiner <hannes@...xchg.org>, 
	David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, 
	linux-kernel@...r.kernel.org, Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH v3 04/15] mm, swap: check page poison flag after locking it

On Wed, Sep 10, 2025 at 9:09 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> Instead of checking the poison flag only in the fast swap cache lookup
> path, always check the poison flags after locking a swap cache folio.
>
> There are two reasons to do so.
>
> The folio is unstable and could be removed from the swap cache anytime,
> so it's totally possible that the folio is no longer the backing folio
> of a swap entry, and could be an irrelevant poisoned folio. We might
> mistakenly kill a faulting process.
>
> And it's totally possible or even common for the slow swap in path
> (swapin_readahead) to bring in a cached folio. The cache folio could be
> poisoned, too. Only checking the poison flag in the fast path will miss
> such folios.
>
> The race window is tiny, so it's very unlikely to happen, though.
> While at it, also add a unlikely prefix.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Acked-by: Chris Li <chrisl@...nel.org>

Acked-by: Nhat Pham <nphamcs@...il.com>