From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Ayush Ranjan <ayushr@modal.com>, Hugh Dickins <hughd@google.com>,
Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>,
Gregory Price <gourry@gourry.net>,
Pedro Falcato <pedro.falcato@gmail.com>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [BUG] shmem: FALLOC_FL_PUNCH_HOLE vs fault-around race corrupts page cache / rss counters
Date: Thu, 24 Sep 2026 09:12:31 +0200 [thread overview]
Message-ID: <1e4580ab-75dd-4092-8afd-69180d064942@kernel.org> (raw)
In-Reply-To: <20260924061708.1645968-1-ayushr@modal.com>
On 9/24/26 08:16, Ayush Ranjan wrote:
> Hi,
>
> We are seeing shmem/tmpfs page cache corruption on production hosts
> running a workload that punches holes in a memfd (hole-punch based
> memory reclaim) while other threads and forked children fault the
> same MAP_SHARED mapping. The kernel taints but does not oops:
>
> BUG: Bad page cache in process ... pfn:...
> page dumped because: still mapped when deleted
> ...
> dentry name(?): "memfd:..."
>
> and, more frequently, a paired rss-counter imbalance when the mm is
> torn down, always exactly one PMD-order folio (512 pages):
>
> BUG: Bad rss-counter state mm:... type:MM_FILEPAGES val:-512
> BUG: Bad rss-counter state mm:... type:MM_SHMEMPAGES val:512
>
> Seen on 6.12 and 6.18, x86_64, bare metal and VM, with
> /sys/kernel/mm/transparent_hugepage/shmem_enabled = always.
>
> This looks like the same corruption Gregory reported in March, which
> as far as I can tell stalled without a fix; that report needed ~100
> ballooning VMs to reproduce:
>
> https://patchew.org/linux/20260326162611.693539-1-gourry@gourry.net/
Indeed, it looks like what was reported in
https://lore.kernel.org/all/20260326162611.693539-1-gourry@gourry.net/
--
Cheers,
David
next prev parent reply other threads:[~2026-09-24 7:12 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-24 6:16 Ayush Ranjan
2026-09-24 7:12 ` David Hildenbrand (Arm) [this message]
2026-09-24 8:34 ` Pedro Falcato
2026-09-24 9:15 ` Jan Kara
2026-09-24 9:30 ` Baolin Wang
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