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 8C44B82C8E; Wed, 7 Aug 2024 15:14:39 +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=1723043679; cv=none; b=INBMav7Q63ig5zkSlLaSDO//rLFOJLzPjGd4vH+ph3GmNhILlLbEg8+fpgIoZogvH5qdcG+zAnwwa12YphpFf1XyQ8zJoBax2pekcMF1DXbwMvKNocIli9/90wLytiU/HJcVE07oGQKUhLO2danGmq8SoXJJyiFNk9hPJvB2Ivs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723043679; c=relaxed/simple; bh=bhH9NL/qy4k0wNB0sxyxcU6lm78frZOHzoM2+81Twg0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=G/UQtJ50G/K7UEEKNg3OL0i0cJCCKKM4TEoTnF11w/xq/AKMWW9q8MpAtDjBtOaBYSn8f5TXH2kxbXlMbGq5pBQxsMhmximJ6uCAjCW2nVFan1ulbZCQwaulxTC8mDXv20uxLtTNgPHk/3/0W7lAkCNHJmKJljPHbVXlT7HmR1k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=v/ZlE1oa; 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="v/ZlE1oa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C6CEC32781; Wed, 7 Aug 2024 15:14:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1723043679; bh=bhH9NL/qy4k0wNB0sxyxcU6lm78frZOHzoM2+81Twg0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=v/ZlE1oaZy9JwTgv2AmMmrgVZ0KXRkqpguBYsOFnbcdakFGEGo3xT0g+CcQlxtYOy /4uWgY4w/owfkPVd9flI3E1hrs/8o7edC7tBBBkYwzvGcGuO6kg2lnddbTK0+9pJYN v9L4vlbwOBcj3cwf+IjmM3Hrk/+pBekBc4xOJJDU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Li Zhijian , Yao Xingtao , Vlastimil Babka , David Hildenbrand , Andrew Morton , Sasha Levin Subject: [PATCH 6.1 22/86] mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist() Date: Wed, 7 Aug 2024 17:00:01 +0200 Message-ID: <20240807150039.969311524@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240807150039.247123516@linuxfoundation.org> References: <20240807150039.247123516@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Li Zhijian [ Upstream commit 66eca1021a42856d6af2a9802c99e160278aed91 ] It's expected that no page should be left in pcp_list after calling zone_pcp_disable() in offline_pages(). Previously, it's observed that offline_pages() gets stuck [1] due to some pages remaining in pcp_list. Cause: There is a race condition between drain_pages_zone() and __rmqueue_pcplist() involving the pcp->count variable. See below scenario: CPU0 CPU1 ---------------- --------------- spin_lock(&pcp->lock); __rmqueue_pcplist() { zone_pcp_disable() { /* list is empty */ if (list_empty(list)) { /* add pages to pcp_list */ alloced = rmqueue_bulk() mutex_lock(&pcp_batch_high_lock) ... __drain_all_pages() { drain_pages_zone() { /* read pcp->count, it's 0 here */ count = READ_ONCE(pcp->count) /* 0 means nothing to drain */ /* update pcp->count */ pcp->count += alloced << order; ... ... spin_unlock(&pcp->lock); In this case, after calling zone_pcp_disable() though, there are still some pages in pcp_list. And these pages in pcp_list are neither movable nor isolated, offline_pages() gets stuck as a result. Solution: Expand the scope of the pcp->lock to also protect pcp->count in drain_pages_zone(), to ensure no pages are left in the pcp list after zone_pcp_disable() [1] https://lore.kernel.org/linux-mm/6a07125f-e720-404c-b2f9-e55f3f166e85@fujitsu.com/ Link: https://lkml.kernel.org/r/20240723064428.1179519-1-lizhijian@fujitsu.com Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") Signed-off-by: Li Zhijian Reported-by: Yao Xingtao Reviewed-by: Vlastimil Babka Cc: David Hildenbrand Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/page_alloc.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4029d13636ece..a905b850d31c4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3177,16 +3177,20 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) static void drain_pages_zone(unsigned int cpu, struct zone *zone) { struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); - int count = READ_ONCE(pcp->count); - - while (count) { - int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); - count -= to_drain; + int count; + do { spin_lock(&pcp->lock); - free_pcppages_bulk(zone, to_drain, pcp, 0); + count = pcp->count; + if (count) { + int to_drain = min(count, + pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); + + free_pcppages_bulk(zone, to_drain, pcp, 0); + count -= to_drain; + } spin_unlock(&pcp->lock); - } + } while (count); } /* -- 2.43.0