From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx200.postini.com [74.125.245.200]) by kanga.kvack.org (Postfix) with SMTP id EA9306B005A for ; Thu, 14 Jun 2012 01:31:05 -0400 (EDT) Message-ID: <4FD97718.6060008@kernel.org> Date: Thu, 14 Jun 2012 14:31:04 +0900 From: Minchan Kim MIME-Version: 1.0 Subject: Re: [PATCH] memory hotplug: fix invalid memory access caused by stale kswapd pointer References: <1339645491-5656-1-git-send-email-jiang.liu@huawei.com> In-Reply-To: <1339645491-5656-1-git-send-email-jiang.liu@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jiang Liu Cc: Mel Gorman , KOSAKI Motohiro , KAMEZAWA Hiroyuki , Andrew Morton , Hugh Dickins , Keping Chen , Tony Luck , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xishi Qiu , Jiang Liu Hi, On 06/14/2012 12:44 PM, Jiang Liu wrote: > Function kswapd_stop() will be called to destroy the kswapd work thread > when all memory of a NUMA node has been offlined. But kswapd_stop() only > terminates the work thread without resetting NODE_DATA(nid)->kswapd to NULL. > The stale pointer will prevent kswapd_run() from creating a new work thread > when adding memory to the memory-less NUMA node again. Eventually the stale > pointer may cause invalid memory access. > > Signed-off-by: Xishi Qiu > Signed-off-by: Jiang Liu Reviewed-by: Minchan Kim Nitpick: I saw kswapd_run and doubt why following line is there. if (pgdat->kswapd) return 0; As looking thorough hotplug, I realized one can hotplug pages which are within different zones but same node. Because kswapd live in per-node, that code is for checking kswapd already run. Right? IMHO, better readable code is following as diff --git a/include/linux/swap.h b/include/linux/swap.h index b967eda..9425c0e 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -299,6 +299,7 @@ static inline void scan_unevictable_unregister_node(struct node *node) } #endif +extern bool is_kswapd_running(int nid); extern int kswapd_run(int nid); extern void kswapd_stop(int nid); #ifdef CONFIG_CGROUP_MEM_RES_CTLR diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 0d7e3ec..60f9155 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -522,7 +522,8 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages) init_per_zone_wmark_min(); if (onlined_pages) { - kswapd_run(zone_to_nid(zone)); + if (!is_kswapd_running(zone_to_nid(zone)) + kswapd_run(zone_to_nid(zone)); node_set_state(zone_to_nid(zone), N_HIGH_MEMORY); } diff --git a/mm/vmscan.c b/mm/vmscan.c index eeb3bc9..f331904 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2932,6 +2932,14 @@ static int __devinit cpu_callback(struct notifier_block *nfb, return NOTIFY_OK; } +bool is_kswapd_running(int nid) +{ + pg_data_t *pgdat = NODE_DATA(nid); + if (pgdat->kswapd) + return true; + return false; +} + /* * This kswapd start function will be called by init and node-hot-add. * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. @@ -2941,9 +2949,6 @@ int kswapd_run(int nid) pg_data_t *pgdat = NODE_DATA(nid); int ret = 0; - if (pgdat->kswapd) - return 0; - pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); if (IS_ERR(pgdat->kswapd)) { /* failure at boot is fatal */ Anyway, it's a preference and trivial but I hope you fix that, too if you don't mind Of course, my nitpick shouldn't prevent merging your good fix. If you mind it, I don't care of it. :) Thanks. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org