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[PATCH] arm64: replace read_lock to rcu lock in call_step_hook

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  [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Yang Shi <yang.shi@linaro.org> - 2016-02-09 00:20 +0100
    Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-02-09 10:10 +0100
    Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Will Deacon <will.deacon@arm.com> - 2016-02-09 16:00 +0100
      Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Steven Rostedt <rostedt@goodmis.org> - 2016-02-09 16:10 +0100
        Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Will Deacon <will.deacon@arm.com> - 2016-02-09 17:10 +0100
          Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Steven Rostedt <rostedt@goodmis.org> - 2016-02-09 17:20 +0100
          Re: [PATCH] arm64: replace read_lock to rcu lock in call_step_hook Catalin Marinas <catalin.marinas@arm.com> - 2016-02-09 17:30 +0100

#1329678 — [PATCH] arm64: replace read_lock to rcu lock in call_step_hook

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.

Signed-off-by: Yang Shi <yang.shi@linaro.org>
---
 arch/arm64/kernel/debug-monitors.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 8aee3ae..c1492ba 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -186,20 +186,21 @@ static void clear_regs_spsr_ss(struct pt_regs *regs)
 
 /* EL1 Single Step Handler hooks */
 static LIST_HEAD(step_hook);
-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();
 }
 
 /*
@@ -213,15 +214,15 @@ 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;
 }
-- 
2.0.2

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#1329976

* Yang Shi | 2016-02-08 14:49:24 [-0800]:

>BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
…
>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.

I am going to apply this for -RT.

Sebastian

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#1330306

On Mon, Feb 08, 2016 at 02:49:24PM -0800, Yang Shi wrote:
> 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.
> 
> Signed-off-by: Yang Shi <yang.shi@linaro.org>

Acked-by: Will Deacon <will.deacon@arm.com>

Will

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#1330318

On Tue, 9 Feb 2016 14:54:26 +0000
Will Deacon <will.deacon@arm.com> wrote:


> Acked-by: Will Deacon <will.deacon@arm.com>

Will,

The patch looks good to me. Do you want to take it through your tree?

It benefits mainline too as a rcu_read_lock() is more efficient than
rwlocks. Although I will say this is a slow path anyway.

-- Steve

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#1330398

On Tue, Feb 09, 2016 at 10:07:58AM -0500, Steven Rostedt wrote:
> On Tue, 9 Feb 2016 14:54:26 +0000
> Will Deacon <will.deacon@arm.com> wrote:
> 
> 
> > Acked-by: Will Deacon <will.deacon@arm.com>
> 
> Will,

Hi Steve,

> The patch looks good to me. Do you want to take it through your tree?
> 
> It benefits mainline too as a rcu_read_lock() is more efficient than
> rwlocks. Although I will say this is a slow path anyway.

I was thinking that Catalin would queue it for 4.6 in the arm64 tree,
since that's probably easiest in case any unlikely conflicts crop up.

Will

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#1330434

On Tue, 9 Feb 2016 16:04:42 +0000
Will Deacon <will.deacon@arm.com> wrote:
 
> > The patch looks good to me. Do you want to take it through your tree?
> > 
> > It benefits mainline too as a rcu_read_lock() is more efficient than
> > rwlocks. Although I will say this is a slow path anyway.  
> 
> I was thinking that Catalin would queue it for 4.6 in the arm64 tree,
> since that's probably easiest in case any unlikely conflicts crop up.

Oh, OK.

That's fine. I just didn't want you to think that the RT folks were
going to pull it in for mainline.

-- Steve

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#1330439

On Tue, Feb 09, 2016 at 04:04:42PM +0000, Will Deacon wrote:
> On Tue, Feb 09, 2016 at 10:07:58AM -0500, Steven Rostedt wrote:
> > On Tue, 9 Feb 2016 14:54:26 +0000
> > Will Deacon <will.deacon@arm.com> wrote:
> > 
> > 
> > > Acked-by: Will Deacon <will.deacon@arm.com>
> 
> > The patch looks good to me. Do you want to take it through your tree?
> > 
> > It benefits mainline too as a rcu_read_lock() is more efficient than
> > rwlocks. Although I will say this is a slow path anyway.
> 
> I was thinking that Catalin would queue it for 4.6 in the arm64 tree,
> since that's probably easiest in case any unlikely conflicts crop up.

Queued.

-- 
Catalin

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