linux-kernel - Re: [PATCH RT 07/17] arm64: replace read_lock to rcu lock in call_step

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Date:	Thu, 3 Mar 2016 09:53:00 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Kacur <jkacur@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	stable-rt@...r.kernel.org, Yang Shi <yang.shi@...aro.org>
Subject: Re: [PATCH RT 07/17] arm64: replace read_lock to rcu lock in
 call_step_hook

Hi Steven,

On 02/03/2016:10:44:40 AM, Steven Rostedt wrote:
> 3.14.61-rt64-rc1 stable review patch.
> If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Yang Shi <yang.shi@...aro.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-rt@...r.kernel.org
> Signed-off-by: Yang Shi <yang.shi@...aro.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.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);

I think, this got wrong during backporting, no?
Should have been
-DEFINE_RWLOCK(step_hook_lock);

> +static DEFINE_SPINLOCK(step_hook_lock);

~Pratyush