From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id F03B66B004A for ; Wed, 1 Dec 2010 00:29:20 -0500 (EST) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id oB15TIuC016991 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Wed, 1 Dec 2010 14:29:19 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id D52F045DE68 for ; Wed, 1 Dec 2010 14:29:18 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id AE2C845DE55 for ; Wed, 1 Dec 2010 14:29:18 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id A0AA01DB803B for ; Wed, 1 Dec 2010 14:29:18 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.249.87.105]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 5ED141DB803F for ; Wed, 1 Dec 2010 14:29:18 +0900 (JST) From: KOSAKI Motohiro Subject: [PATCH 2/2] ksm: annotate ksm_thread_mutex is no deadlock source In-Reply-To: <20101026163218.B7BF.A69D9226@jp.fujitsu.com> References: <20101026163218.B7BF.A69D9226@jp.fujitsu.com> Message-Id: <20101201143008.ABCE.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Wed, 1 Dec 2010 14:29:17 +0900 (JST) Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Hugh Dickins , Andrew Morton , Andrea Arcangeli , Andi Kleen , LKML , linux-mm , KAMEZAWA Hiroyuki List-ID: commit 62b61f611e(ksm: memory hotremove migration only) made following new lockdep warning. ======================================================= [ INFO: possible circular locking dependency detected ] ------------------------------------------------------- bash/1621 is trying to acquire lock: ((memory_chain).rwsem){.+.+.+}, at: [] __blocking_notifier_call_chain+0x69/0xc0 but task is already holding lock: (ksm_thread_mutex){+.+.+.}, at: [] ksm_memory_callback+0x3a/0xc0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (ksm_thread_mutex){+.+.+.}: [] lock_acquire+0xaa/0x140 [] __mutex_lock_common+0x44/0x3f0 [] mutex_lock_nested+0x48/0x60 [] ksm_memory_callback+0x3a/0xc0 [] notifier_call_chain+0x8c/0xe0 [] __blocking_notifier_call_chain+0x7e/0xc0 [] blocking_notifier_call_chain+0x16/0x20 [] memory_notify+0x1b/0x20 [] remove_memory+0x1cc/0x5f0 [] memory_block_change_state+0xfd/0x1a0 [] store_mem_state+0xe2/0xf0 [] sysdev_store+0x20/0x30 [] sysfs_write_file+0xe6/0x170 [] vfs_write+0xc8/0x190 [] sys_write+0x54/0x90 [] system_call_fastpath+0x16/0x1b -> #0 ((memory_chain).rwsem){.+.+.+}: [] __lock_acquire+0x155a/0x1600 [] lock_acquire+0xaa/0x140 [] down_read+0x51/0xa0 [] __blocking_notifier_call_chain+0x69/0xc0 [] blocking_notifier_call_chain+0x16/0x20 [] memory_notify+0x1b/0x20 [] remove_memory+0x56e/0x5f0 [] memory_block_change_state+0xfd/0x1a0 [] store_mem_state+0xe2/0xf0 [] sysdev_store+0x20/0x30 [] sysfs_write_file+0xe6/0x170 [] vfs_write+0xc8/0x190 [] sys_write+0x54/0x90 [] system_call_fastpath+0x16/0x1b But it's false positive. Both memory_chain.rwsem and ksm_thread_mutex have outer lock (mem_hotplug_mutex). then, they can't make deadlock. Thus, This patch annotate ksm_thread_mutex is not deadlock source. Signed-off-by: KOSAKI Motohiro --- mm/ksm.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 65ab5c7..5aa4900 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1724,8 +1724,10 @@ static int ksm_memory_callback(struct notifier_block *self, /* * Keep it very simple for now: just lock out ksmd and * MADV_UNMERGEABLE while any memory is going offline. + * Mutex_lock_nested() is necessary to tell that + * ksm_thread_mutex is not unlocked here intentionally. */ - mutex_lock(&ksm_thread_mutex); + mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING); break; case MEM_OFFLINE: -- 1.6.5.2 -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org