From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zhong Subject: [RFC PATCH next] fix unpaired rcu lock in prepend_path() Date: Wed, 13 Nov 2013 15:21:51 +0800 Message-ID: <1384327311.19669.8.camel@ThinkPad-T5421> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from e23smtp07.au.ibm.com ([202.81.31.140]:39594 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758427Ab3KMHWJ (ORCPT ); Wed, 13 Nov 2013 02:22:09 -0500 Received: from /spool/local by e23smtp07.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 13 Nov 2013 17:22:06 +1000 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [9.190.235.152]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id 2C6A72BB0052 for ; Wed, 13 Nov 2013 18:21:56 +1100 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id rAD747a27995892 for ; Wed, 13 Nov 2013 18:04:08 +1100 Received: from d23av03.au.ibm.com (localhost [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id rAD7LsOP005715 for ; Wed, 13 Nov 2013 18:21:54 +1100 Sender: linux-next-owner@vger.kernel.org List-ID: To: linux-next list Cc: Al Viro The patch tries to fix following complaint(next-1112) caused by unpaired rcu_read_lock/unlock in function prepend_path(): [ 19.611017] ===================================== [ 19.612052] [ BUG: bad unlock balance detected! ] [ 19.612052] 3.12.0-next-20131112 #1 Tainted: G W [ 19.612052] ------------------------------------- [ 19.612052] systemd/1 is trying to release lock (rcu_read_lock) at: [ 19.612052] [] d_path+0x17e/0x270 [ 19.612052] but there are no more locks to release! [ 19.612052] other info that might help us debug this: [ 19.612052] 2 locks held by systemd/1: [ 19.612052] #0: (&p->lock){+.+.+.}, at: [] seq_read+0x3d/0x3c0 [ 19.612052] #1: (&mm->mmap_sem){++++++}, at: [] m_start+0xa7/0x190 [ 19.612052] stack backtrace: [ 19.612052] CPU: 0 PID: 1 Comm: systemd Tainted: G W 3.12.0-next-20131112 #1 [ 19.612052] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 [ 19.612052] ffffffff811cd22e ffff88011b07dbf8 ffffffff8154a067 0000000000000001 [ 19.623937] ffff880119cc0000 ffff88011b07dc28 ffffffff810a91ee ffffffff811ccace [ 19.623937] ffffffff81a38a80 ffffffff811cd22e 00000000ffffffff ffff88011b07dcc8 [ 19.623937] Call Trace: [ 19.623937] [] ? d_path+0x17e/0x270 [ 19.629627] [] dump_stack+0x4f/0x7c [ 19.629627] [] print_unlock_imbalance_bug+0xfe/0x110 [ 19.629627] [] ? prepend_path+0x25e/0x4a0 [ 19.629627] [] ? d_path+0x17e/0x270 [ 19.629627] [] lock_release_non_nested+0x1ee/0x310 [ 19.629627] [] ? _raw_spin_unlock+0x35/0x60 [ 19.629627] [] ? prepend_path+0x25e/0x4a0 [ 19.629627] [] ? d_path+0x169/0x270 [ 19.629627] [] ? d_path+0x17e/0x270 [ 19.629627] [] lock_release+0xc4/0x340 [ 19.629627] [] d_path+0x196/0x270 [ 19.629627] [] ? seq_path+0x51/0xd0 [ 19.629627] [] seq_path+0x51/0xd0 [ 19.629627] [] show_map_vma+0x156/0x290 [ 19.629627] [] ? m_start+0xa7/0x190 [ 19.629627] [] show_map+0x2f/0x90 [ 19.629627] [] show_pid_map+0x13/0x20 [ 19.629627] [] seq_read+0x246/0x3c0 [ 19.629627] [] vfs_read+0xb0/0x180 [ 19.629627] [] SyS_read+0x52/0xa0 [ 19.629627] [] tracesys+0xd0/0xd5 [ 19.645347] ------------[ cut here ]------------ Signed-off-by: Li Zhong --- fs/dcache.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index ef2f32f..555a371 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2910,6 +2910,7 @@ static int prepend_path(const struct path *path, restart_mnt: read_seqbegin_or_lock(&mount_lock, &m_seq); seq = 0; + rcu_read_lock(); restart: bptr = *buffer; blen = *buflen; @@ -2957,6 +2958,9 @@ restart: goto restart; } done_seqretry(&rename_lock, seq); + + if (!(m_seq & 1)) + rcu_read_unlock(); if (need_seqretry(&mount_lock, m_seq)) { m_seq = 1; goto restart_mnt;