[v2,4/4] arm64: Remove unneeded rcu_read_lock from debug handlers
diff mbox series

Message ID 156378175027.12011.5591853683946780785.stgit@devnote2
State Superseded
Headers show
Series
  • arm64: kprobes: Fix some bugs in arm64 kprobes
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Commit Message

Masami Hiramatsu July 22, 2019, 7:49 a.m. UTC
Remove rcu_read_lock()/rcu_read_unlock() from debug exception
handlers since we are sure those are not preemptible and
interrupts are off.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
---
 arch/arm64/kernel/debug-monitors.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Comments

Paul E. McKenney July 22, 2019, 12:07 p.m. UTC | #1
On Mon, Jul 22, 2019 at 04:49:11PM +0900, Masami Hiramatsu wrote:
> Remove rcu_read_lock()/rcu_read_unlock() from debug exception
> handlers since we are sure those are not preemptible and
> interrupts are off.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.ibm.com>

From an RCU viewpoint:

Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>

> ---
>  arch/arm64/kernel/debug-monitors.c |   14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index f8719bd30850..48222a4760c2 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -207,16 +207,16 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr)
>  
>  	list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
>  
> -	rcu_read_lock();
> -
> +	/*
> +	 * Since single-step exception disables interrupt, this function is
> +	 * entirely not preemptible, and we can use rcu list safely here.
> +	 */
>  	list_for_each_entry_rcu(hook, list, node)	{
>  		retval = hook->fn(regs, esr);
>  		if (retval == DBG_HOOK_HANDLED)
>  			break;
>  	}
>  
> -	rcu_read_unlock();
> -
>  	return retval;
>  }
>  NOKPROBE_SYMBOL(call_step_hook);
> @@ -305,14 +305,16 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr)
>  
>  	list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
>  
> -	rcu_read_lock();
> +	/*
> +	 * Since brk exception disables interrupt, this function is
> +	 * entirely not preemptible, and we can use rcu list safely here.
> +	 */
>  	list_for_each_entry_rcu(hook, list, node) {
>  		unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
>  
>  		if ((comment & ~hook->mask) == hook->imm)
>  			fn = hook->fn;
>  	}
> -	rcu_read_unlock();
>  
>  	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
>  }
>

Patch
diff mbox series

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index f8719bd30850..48222a4760c2 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -207,16 +207,16 @@  static int call_step_hook(struct pt_regs *regs, unsigned int esr)
 
 	list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
 
-	rcu_read_lock();
-
+	/*
+	 * Since single-step exception disables interrupt, this function is
+	 * entirely not preemptible, and we can use rcu list safely here.
+	 */
 	list_for_each_entry_rcu(hook, list, node)	{
 		retval = hook->fn(regs, esr);
 		if (retval == DBG_HOOK_HANDLED)
 			break;
 	}
 
-	rcu_read_unlock();
-
 	return retval;
 }
 NOKPROBE_SYMBOL(call_step_hook);
@@ -305,14 +305,16 @@  static int call_break_hook(struct pt_regs *regs, unsigned int esr)
 
 	list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
 
-	rcu_read_lock();
+	/*
+	 * Since brk exception disables interrupt, this function is
+	 * entirely not preemptible, and we can use rcu list safely here.
+	 */
 	list_for_each_entry_rcu(hook, list, node) {
 		unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
 
 		if ((comment & ~hook->mask) == hook->imm)
 			fn = hook->fn;
 	}
-	rcu_read_unlock();
 
 	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
 }