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] [<ffffffff811cd22e>] 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: [<ffffffff811dd27d>] seq_read+0x3d/0x3c0 [ 19.612052] #1: (&mm->mmap_sem){++++++}, at: [<ffffffff81228037>] 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] [<ffffffff811cd22e>] ? d_path+0x17e/0x270 [ 19.629627] [<ffffffff8154a067>] dump_stack+0x4f/0x7c [ 19.629627] [<ffffffff810a91ee>] print_unlock_imbalance_bug+0xfe/0x110 [ 19.629627] [<ffffffff811ccace>] ? prepend_path+0x25e/0x4a0 [ 19.629627] [<ffffffff811cd22e>] ? d_path+0x17e/0x270 [ 19.629627] [<ffffffff810ad70e>] lock_release_non_nested+0x1ee/0x310 [ 19.629627] [<ffffffff815519c5>] ? _raw_spin_unlock+0x35/0x60 [ 19.629627] [<ffffffff811ccace>] ? prepend_path+0x25e/0x4a0 [ 19.629627] [<ffffffff811cd219>] ? d_path+0x169/0x270 [ 19.629627] [<ffffffff811cd22e>] ? d_path+0x17e/0x270 [ 19.629627] [<ffffffff810ad8f4>] lock_release+0xc4/0x340 [ 19.629627] [<ffffffff811cd246>] d_path+0x196/0x270 [ 19.629627] [<ffffffff811dd651>] ? seq_path+0x51/0xd0 [ 19.629627] [<ffffffff811dd651>] seq_path+0x51/0xd0 [ 19.629627] [<ffffffff81228276>] show_map_vma+0x156/0x290 [ 19.629627] [<ffffffff81228037>] ? m_start+0xa7/0x190 [ 19.629627] [<ffffffff812283df>] show_map+0x2f/0x90 [ 19.629627] [<ffffffff81228473>] show_pid_map+0x13/0x20 [ 19.629627] [<ffffffff811dd486>] seq_read+0x246/0x3c0 [ 19.629627] [<ffffffff811b4030>] vfs_read+0xb0/0x180 [ 19.629627] [<ffffffff811b42a2>] SyS_read+0x52/0xa0 [ 19.629627] [<ffffffff8155a262>] tracesys+0xd0/0xd5 [ 19.645347] ------------[ cut here ]------------ Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx> --- 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; -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html