From: David Hildenbrand <david@redhat.com>
To: Shivank Garg <shivankg@amd.com>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com,
lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com,
npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com,
fengwei.yin@intel.com, bharata@amd.com,
syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com
Subject: Re: [PATCH V2 2/2] mm/khugepaged: fix race with folio split/free using temporary reference
Date: Sat, 24 May 2025 23:48:01 +0200 [thread overview]
Message-ID: <5815d9ed-e59f-4129-b20b-a0c07a2cf874@redhat.com> (raw)
In-Reply-To: <20250523091432.17588-2-shivankg@amd.com>
On 23.05.25 11:14, Shivank Garg wrote:
> hpage_collapse_scan_file() calls folio_expected_ref_count(), which in turn
> calls folio_mapcount(). folio_mapcount() checks folio_test_large() before
> proceeding to folio_large_mapcount(), but there is a race window where the
> folio may get split/freed between these checks, triggering:
>
> VM_WARN_ON_FOLIO(!folio_test_large(folio), folio)
>
> Take a temporary reference to the folio in hpage_collapse_scan_file().
> This stabilizes the folio during refcount check and prevents incorrect
> large folio detection due to concurrent split/free.
>
> Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value")
> Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Shivank Garg <shivankg@amd.com>
> ---
> V1: https://lore.kernel.org/linux-mm/20250522093452.6379-1-shivankg@amd.com
> ---
Assuming we have this as patch #1:
Acked-by: David Hildenbrand <david@redhat.com>
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2025-05-24 21:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-05-23 9:14 [PATCH V2 1/2] mm/khugepaged: clean up refcount check using folio_expected_ref_count() Shivank Garg
2025-05-23 9:14 ` [PATCH V2 2/2] mm/khugepaged: fix race with folio split/free using temporary reference Shivank Garg
2025-05-24 21:48 ` David Hildenbrand [this message]
2025-05-24 21:47 ` [PATCH V2 1/2] mm/khugepaged: clean up refcount check using folio_expected_ref_count() David Hildenbrand
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