From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD1457D098 for ; Fri, 20 Jun 2025 09:16:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750411002; cv=none; b=rE1mk0g5OR+v4yPewV0lUpRJ00sjiC8SOEokekrW0P/SH1BCBWADs7U4VwYkKhEksl7/66yJZFQFfaFOVMlb00s6BlPKVknuwUTf3GI4jpvbzSdszQStH+NQQpHdWm/MZ8kxLY0a/TmEdgTqfpWXWgkHjTriaqXSIYg/cmpS5lk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750411002; c=relaxed/simple; bh=IaH8xudgdjGtSU+/p2ZZM2/lqcRbMPCel8zXJbKnqIE=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=f3aLOUSoj0mTrUUm/FnObCc0iPiK0RuXseWjbNixa8u8hPm618YguDm/NiY9tY5E4SNJ0E55bdYg8oQ6nELL9+1umqIz8uhYdlA5rxJRdjrXlYIZRdVplWhjurQsKwL4il8QrKqBan7BQdgAd5J1HG40A8pkO0vnuCy6heQzKYA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=2YuKb55L; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="2YuKb55L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB588C4CEE3; Fri, 20 Jun 2025 09:16:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750411002; bh=IaH8xudgdjGtSU+/p2ZZM2/lqcRbMPCel8zXJbKnqIE=; h=Subject:To:Cc:From:Date:From; b=2YuKb55LY/K8MAayA5Upnk+OeEWr/O5/oNeKWrg//YN3i1qNx3K2vTQ8pd7hBJVYN SzmcUR3SK29P8yiDVWF1aJc/kCQ+mSWQM8orWoB6VFksWXZzvFqdvsWXBeXQeyMCNo kg0GX1lZxMGRL/erI9g9hqPyawKT+bVabJXh8J/8= Subject: FAILED: patch "[PATCH] mm/khugepaged: fix race with folio split/free using temporary" failed to apply to 6.15-stable tree To: shivankg@amd.com,akpm@linux-foundation.org,baolin.wang@linux.alibaba.com,bharata@amd.com,david@redhat.com,dev.jain@arm.com,fengwei.yin@intel.com,liam.howlett@oracle.com,lorenzo.stoakes@oracle.com,npache@redhat.com,ryan.roberts@arm.com,stable@vger.kernel.org,ziy@nvidia.com Cc: From: Date: Fri, 20 Jun 2025 11:16:39 +0200 Message-ID: <2025062039-policy-handheld-01c6@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.15.y git checkout FETCH_HEAD git cherry-pick -x 595cf683519ab5a277d258a2251ee8cc7b838d6d # git commit -s git send-email --to '' --in-reply-to '2025062039-policy-handheld-01c6@gregkh' --subject-prefix 'PATCH 6.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 595cf683519ab5a277d258a2251ee8cc7b838d6d Mon Sep 17 00:00:00 2001 From: Shivank Garg Date: Mon, 26 May 2025 18:28:18 +0000 Subject: [PATCH] mm/khugepaged: fix race with folio split/free using temporary reference hpage_collapse_scan_file() calls is_refcount_suitable(), 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. Use helper folio_expected_ref_count() + 1 to compare with folio_ref_count() instead of using is_refcount_suitable(). Link: https://lkml.kernel.org/r/20250526182818.37978-1-shivankg@amd.com Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") Signed-off-by: Shivank Garg Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com Suggested-by: David Hildenbrand Acked-by: David Hildenbrand Acked-by: Dev Jain Reviewed-by: Baolin Wang Cc: Bharata B Rao Cc: Fengwei Yin Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Mariano Pache Cc: Ryan Roberts Cc: Zi Yan Cc: Signed-off-by: Andrew Morton diff --git a/mm/khugepaged.c b/mm/khugepaged.c index cdf5a581368b..7731a162a1a7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2293,6 +2293,17 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, continue; } + if (!folio_try_get(folio)) { + xas_reset(&xas); + continue; + } + + if (unlikely(folio != xas_reload(&xas))) { + folio_put(folio); + xas_reset(&xas); + continue; + } + if (folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start) { /* Maybe PMD-mapped */ @@ -2303,23 +2314,27 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, * it's safe to skip LRU and refcount checks before * returning. */ + folio_put(folio); break; } node = folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + folio_put(folio); break; } cc->node_load[node]++; if (!folio_test_lru(folio)) { result = SCAN_PAGE_LRU; + folio_put(folio); break; } - if (!is_refcount_suitable(folio)) { + if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { result = SCAN_PAGE_COUNT; + folio_put(folio); break; } @@ -2331,6 +2346,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, */ present += folio_nr_pages(folio); + folio_put(folio); if (need_resched()) { xas_pause(&xas);