[PATCH RT 07/17] arm64: replace read_lock to rcu lock in call_step_hook

[Steven Rostedt]

3.14.61-rt64-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Yang Shi <yang....@linaro.org>

BUG: sleeping function called from invalid context at 
kernel/locking/rtmutex.c:917
in_atomic(): 1, irqs_disabled(): 128, pid: 383, name: sh
Preemption disabled at:[<ffff800000124c18>] kgdb_cpu_enter+0x158/0x6b8

CPU: 3 PID: 383 Comm: sh Tainted: G        W       4.1.13-rt13 #2
Hardware name: Freescale Layerscape 2085a RDB Board (DT)
Call trace:
[<ffff8000000885e8>] dump_backtrace+0x0/0x128
[<ffff800000088734>] show_stack+0x24/0x30
[<ffff80000079a7c4>] dump_stack+0x80/0xa0
[<ffff8000000bd324>] ___might_sleep+0x18c/0x1a0
[<ffff8000007a20ac>] __rt_spin_lock+0x2c/0x40
[<ffff8000007a2268>] rt_read_lock+0x40/0x58
[<ffff800000085328>] single_step_handler+0x38/0xd8
[<ffff800000082368>] do_debug_exception+0x58/0xb8
Exception stack(0xffff80834a1e7c80 to 0xffff80834a1e7da0)
7c80: ffffff9c ffffffff 92c23ba0 0000ffff 4a1e7e40 ffff8083 001bfcc4 ffff8000
7ca0: f2000400 00000000 00000000 00000000 4a1e7d80 ffff8083 0049501c ffff8000
7cc0: 00005402 00000000 00aaa210 ffff8000 4a1e7ea0 ffff8083 000833f4 ffff8000
7ce0: ffffff9c ffffffff 92c23ba0 0000ffff 4a1e7ea0 ffff8083 001bfcc0 ffff8000
7d00: 4a0fc400 ffff8083 00005402 00000000 4a1e7d40 ffff8083 00490324 ffff8000
7d20: ffffff9c 00000000 92c23ba0 0000ffff 000a0000 00000000 00000000 00000000
7d40: 00000008 00000000 00080000 00000000 92c23b8b 0000ffff 92c23b8e 0000ffff
7d60: 00000038 00000000 00001cb2 00000000 00000005 00000000 92d7b498 0000ffff
7d80: 01010101 01010101 92be9000 0000ffff 00000000 00000000 00000030 00000000
[<ffff8000000833f4>] el1_dbg+0x18/0x6c

This issue is similar with 62c6c61("arm64: replace read_lock to rcu lock in
call_break_hook"), but comes to single_step_handler.

This also solves kgdbts boot test silent hang issue on 4.4 -rt kernel.

Cc: stable...@vger.kernel.org
Signed-off-by: Yang Shi <yang....@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
 arch/arm64/kernel/debug-monitors.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/debug-monitors.c 
b/arch/arm64/kernel/debug-monitors.c
index 636ba8b6240b..f66d668ffce9 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -190,19 +190,22 @@ static void clear_regs_spsr_ss(struct pt_regs *regs)
 /* EL1 Single Step Handler hooks */
 static LIST_HEAD(step_hook);
 DEFINE_RWLOCK(step_hook_lock);
+static DEFINE_RWLOCK(step_hook_lock);
+static DEFINE_SPINLOCK(step_hook_lock);
 
 void register_step_hook(struct step_hook *hook)
 {
-       write_lock(&step_hook_lock);
-       list_add(&hook->node, &step_hook);
-       write_unlock(&step_hook_lock);
+       spin_lock(&step_hook_lock);
+       list_add_rcu(&hook->node, &step_hook);
+       spin_unlock(&step_hook_lock);
 }
 
 void unregister_step_hook(struct step_hook *hook)
 {
-       write_lock(&step_hook_lock);
-       list_del(&hook->node);
-       write_unlock(&step_hook_lock);
+       spin_lock(&step_hook_lock);
+       list_del_rcu(&hook->node);
+       spin_unlock(&step_hook_lock);
+       synchronize_rcu();
 }
 
 /*
@@ -216,15 +219,15 @@ static int call_step_hook(struct pt_regs *regs, unsigned 
int esr)
        struct step_hook *hook;
        int retval = DBG_HOOK_ERROR;
 
-       read_lock(&step_hook_lock);
+       rcu_read_lock();
 
-       list_for_each_entry(hook, &step_hook, node)     {
+       list_for_each_entry_rcu(hook, &step_hook, node) {
                retval = hook->fn(regs, esr);
                if (retval == DBG_HOOK_HANDLED)
                        break;
        }
 
-       read_unlock(&step_hook_lock);
+       rcu_read_unlock();
 
        return retval;
 }
-- 
2.7.0