From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D6447472777; Tue, 16 Jun 2026 16:31:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781627485; cv=none; b=VtdLfjWJIbuvHMm0A9wNWQ32wLSpzHnk0M/H4/l65Jugc5nEGh+X3p00OnMSoVf87oXPFNbRt6f6Wg6vaYmWPatFpon+w+3uuab8mAG39jzZbGXzwstEENCuiiR+G7108XmbxzZQ/WsVeF4sIm+bB6T0bu/BicEZMCf3t0e7Fb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781627485; c=relaxed/simple; bh=/AKUgPaP2s7IEiFmxdjVG5KSEVo0AsHZ41u2Pq55EiM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cRe8DRXVdqLRFFSvqaHGzqUHWLWrsQgC8vySjjEIYrpD6I3oUHHcQ7VGCGxb9Fm7+UkwONb0JoAJ1Jge/yEngSj86gRpe9uUZR8xRnKysBA7Elo1mAZQ5MwIYwxXh6QVEG8jrqIHlA3aFt02k9B4rC5z9YbWPHmnxJ9iHzfCu3Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=T11zBWzh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="T11zBWzh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D674B1F000E9; Tue, 16 Jun 2026 16:31:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781627484; bh=dBzXC8xCXxmrbwSAO6Xsg+LSckZjSnTiHHCk1mwvRAc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=T11zBWzhWXh3gI+9AybnpYPXDvT+K8PMyTl6zTkTlRsazIjv8M4/Vzfw7CR9EV8pS IKtGRk5Irg+RLo4+zKnZ3V7vCdTCSfA/xpazZMea+BHVxCfg4IqM/9esSE/UGPCegl dXKDmCr1qF3FCsEFLhZ1HfCalXsom1vddwwXDQnA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SeongJae Park , Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton Subject: [PATCH 6.12 149/261] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Tue, 16 Jun 2026 20:29:47 +0530 Message-ID: <20260616145051.981258779@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145044.869532709@linuxfoundation.org> References: <20260616145044.869532709@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: SeongJae Park commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef upstream. damon_get_folio() speculatively calls folio_test_lru() before folio_try_get(). The folio can get freed and reallocated to a tail page. In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. Remove the speculative call. Also mark folio_test_lru() check right after folio_try_get() success as no more unlikely. The race should be rare. Also the problem can happen only if the kernel has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue has been made so far. This fix is based on only theoretical analysis. That said, a bug is a bug. A similar issue was also fixed via commit 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a reference in next_uptodate_folio()"). I don't expect this change will make a meaningful impact to DAMON performance in the real world, though I will be happy to be corrected from the real world reports. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SeongJae Park Cc: Fernand Sieber Cc: Leonard Foerster Cc: Shakeel Butt Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/damon/ops-common.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -28,9 +28,9 @@ struct folio *damon_get_folio(unsigned l return NULL; folio = page_folio(page); - if (!folio_test_lru(folio) || !folio_try_get(folio)) + if (!folio_try_get(folio)) return NULL; - if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) { + if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio)) { folio_put(folio); folio = NULL; }