[PATCH] futex: fix unbalanced spin_lock/spin_unlock() in exit_pi_state_list()

From: Yong Zhang
Date: Thu Feb 28 2013 - 20:37:15 EST

From: Yong Zhang <yong.zhang@xxxxxxxxxxxxx>

Otherwise, below warning is shown somtimes when running some test:

WARNING: at kernel/sched/core.c:3423 migrate_disable+0xbf/0xd0()
Hardware name: OptiPlex 755
Modules linked in: floppy parport parport_pc minix
Pid: 1800, comm: tst-robustpi8 Tainted: G W 3.4.28-rt40 #1
Call Trace:
[<ffffffff81031f3f>] warn_slowpath_common+0x7f/0xc0
[<ffffffff81031f9a>] warn_slowpath_null+0x1a/0x20
[<ffffffff81066eaf>] migrate_disable+0xbf/0xd0
[<ffffffff81085d95>] exit_pi_state_list+0xa5/0x170
[<ffffffff8102f71f>] mm_release+0x12f/0x170
[<ffffffff81036906>] exit_mm+0x26/0x140
[<ffffffff81090fc6>] ? acct_collect+0x186/0x1c0
[<ffffffff81036b66>] do_exit+0x146/0x930
[<ffffffff810658d1>] ? get_parent_ip+0x11/0x50
[<ffffffff8103760d>] do_group_exit+0x4d/0xc0
[<ffffffff8104828f>] get_signal_to_deliver+0x23f/0x6a0
[<ffffffff810019e5>] do_signal+0x65/0x5e0
[<ffffffff81047816>] ? group_send_sig_info+0x76/0x80
[<ffffffff81002018>] do_notify_resume+0x98/0xd0
[<ffffffff8165779b>] int_signal+0x12/0x17
---[ end trace 0000000000000004 ]---

The reason is that spin_lock() is taken in atomic context, but
spin_unlock() is not.

Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
kernel/futex.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 9e26e87..2b676a2 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -562,16 +562,17 @@ void exit_pi_state_list(struct task_struct *curr)


- raw_spin_lock_irq(&curr->pi_lock);
* We dropped the pi-lock, so re-check whether this
* task still owns the PI-state:
if (head->next != next) {
+ raw_spin_lock_irq(&curr->pi_lock);

+ raw_spin_lock_irq(&curr->pi_lock);
WARN_ON(pi_state->owner != curr);

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