linux-kernel - Re: [PATCH] mm/shmem: fix uninitialized folio in shmem

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Message-ID: <9c4b8d43-1c01-46f0-8e1e-435a19b8713b@linux.alibaba.com>
Date: Wed, 7 Jan 2026 09:16:11 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Brian Foster <bfoster@...hat.com>, Barry Song <21cnbao@...il.com>,
 akpm@...ux-foundation.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Hugh Dickins <hughd@...gle.com>,
 syzbot+178fff6149127421c2cc@...kaller.appspotmail.com
Subject: Re: [PATCH] mm/shmem: fix uninitialized folio in shmem_symlink



On 1/7/26 2:46 AM, Matthew Wilcox wrote:
> On Tue, Jan 06, 2026 at 11:47:44AM +0800, Baolin Wang wrote:
>> Why I prefer Barry's fix: First, the symlink folio is marked Uptodate after
>> copying the symlink name, but the whole folio hasn’t been initialized, which
>> seems unreasonable to me. Second, as I said before, using the 'PG_owner_2'
>> flag to mark this uncommon case doesn’t seem worthwhile. Currently, IIUC the
>> 'PG_owner_2' is only used by btrfs; if we ever want to remove the
>> 'PG_owner_2', this uncommon symlink case shouldn’t block its removal.
> 
> PG_owner_2 is aliased with PG_mappedtodisk [1], so it's used by every
> filesystem which uses buffer_heads (whether mentioned in that filesystem
> or not).  btrfs was switched from using private_2 to using owner_2
> a little over a year ago.  PG_owner_2 is not on the list of flags to be
> removed; that's PG_private, PG_private_2 and PG_reserved.

OK. Thanks for the explanation. I understand the plan.