From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout.efficios.com (smtpout.efficios.com [158.69.130.18]) (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 3178422DFB4 for ; Wed, 12 Mar 2025 14:10:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=158.69.130.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741788629; cv=none; b=bV6iKhMsXM55xdCJBKKWxLBkJs+yk06qbY2FC/tK0V/ZD0V0nN7F9ibypQJnUwlRxK+FNvB82pea/0jBuX6S3gOreW8SsVoV+RChhHp9Y7CBs6JjdlftZ68nGAEvCM0Mo0DEVVXaGxCXFNL51zeEw5PW9W8DZrNAfIMC4JRf1DI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741788629; c=relaxed/simple; bh=MipAKpvbmNfmxW0K3rXTS/6tsgSsxzcTZj33h5g1JrI=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=ncg4BVnIO5jtFngMze9lcGyrBNAVZB738xOzp2pLdVhMB3+55XFmm21YGTGCCMTUH13tRdms9KHRW7P2WzfQEiKbnpCG2fTjnjX5VWxhkb4TBrfHpq9Pl5K+QXn+dP7S4R8EII7rCmlRAm9NowJfzIMwIIal1/8erULGVo9Wazg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=uVGW78IH; arc=none smtp.client-ip=158.69.130.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="uVGW78IH" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1741788621; bh=MipAKpvbmNfmxW0K3rXTS/6tsgSsxzcTZj33h5g1JrI=; h=From:To:Cc:Subject:Date:From; b=uVGW78IHEoxm9gFvMdpkcmITWNsaQ5rOcxPLphPcpCZwQ0LUDP1G2hqgsniAf4bKA SfBBLPEC2tuoEKbSunREAW5o5Q/Ocv+vZ+L8VeeYcJCDvCOI96GtV1I9r/vYldcx1O aSWGWlBEd0vtoaWZA711XzQRRU5U0n6VB+ritr3GBtm6SUldiy//Rj+gz5L1I8HWf/ 1gcGbmYobSw61GINfuvxei8eRK9M0H4IAEbDyiyFZutMPqD8T4X1eMfhpS0vc1J7WY /8omuRblm0pxfJR+VL/2hz1a4K4oLo/5RvkGv5aEaekyKOKARjKJlNP9RW9/khqhyr Sas4MrG72guyQ== Received: from localhost.localdomain (96-127-217-162.qc.cable.ebox.net [96.127.217.162]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4ZCXb14tPjzV0D; Wed, 12 Mar 2025 10:10:21 -0400 (EDT) From: Mathieu Desnoyers To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Lorenzo Stoakes , Matthew Wilcox , Alan Stern , Andrea Parri , Will Deacon , Peter Zijlstra , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , linux-mm@kvack.org Subject: [PATCH 1/2] mm: Add missing release barrier on PGDAT_RECLAIM_LOCKED unlock Date: Wed, 12 Mar 2025 10:10:13 -0400 Message-Id: <20250312141014.129725-1-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The PGDAT_RECLAIM_LOCKED bit is used to provide mutual exclusion of node reclaim for struct pglist_data using a single bit. It is "locked" with a test_and_set_bit (similarly to a try lock) which provides full ordering with respect to loads and stores done within __node_reclaim(). It is "unlocked" with clear_bit(), which does not provide any ordering with respect to loads and stores done before clearing the bit. The lack of clear_bit() memory ordering with respect to stores within __node_reclaim() can cause a subsequent CPU to fail to observe stores from a prior node reclaim. This is not an issue in practice on TSO (e.g. x86), but it is an issue on weakly-ordered architectures (e.g. arm64). Fix this by using clear_bit_unlock rather than clear_bit to clear PGDAT_RECLAIM_LOCKED with a release memory ordering semantic. This provides stronger memory ordering (release rather than relaxed). Fixes: d773ed6b856a ("mm: test and set zone reclaim lock before starting reclaim") Signed-off-by: Mathieu Desnoyers Cc: Andrew Morton Cc: Lorenzo Stoakes Cc: Matthew Wilcox Cc: Alan Stern Cc: Andrea Parri Cc: Will Deacon Cc: Peter Zijlstra Cc: Boqun Feng Cc: Nicholas Piggin Cc: David Howells Cc: Jade Alglave Cc: Luc Maranget Cc: "Paul E. McKenney" Cc: linux-mm@kvack.org --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index c22175120f5d..d7e27d5c24e7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -7571,7 +7571,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) return NODE_RECLAIM_NOSCAN; ret = __node_reclaim(pgdat, gfp_mask, order); - clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags); + clear_bit_unlock(PGDAT_RECLAIM_LOCKED, &pgdat->flags); if (ret) count_vm_event(PGSCAN_ZONE_RECLAIM_SUCCESS); -- 2.25.1