linux-kernel - Re: [PATCH] context_tracking: Use arch_atomic_*() in __ct_user_enter and __ct_user

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Date:   Fri, 6 Jan 2023 06:53:31 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Genjian <zhanggenjian123@...il.com>
Cc:     frederic@...nel.org, linux-kernel@...r.kernel.org,
        Genjian Zhang <zhanggenjian@...inos.cn>,
        k2ci <kernel-bot@...inos.cn>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] context_tracking: Use arch_atomic_*() in __ct_user_enter
 and __ct_user_exit

On Thu, Nov 10, 2022 at 04:24:43PM +0800, Genjian wrote:
> From: Genjian Zhang <zhanggenjian@...inos.cn>
> 
> vmlinux.o: warning: objtool: __ct_user_enter+0x45: call to
> __kasan_check_write() leaves .noinstr.text section
> vmlinux.o: warning: objtool: __ct_user_exit+0x3f: call to
> __kasan_check_write() leaves .noinstr.text section
> 
> noinstr cannot have atomic_*() functions.because they have explicit
> instrumentation.Switch to arch_ prefixed atomic operation functions to
> avoid the explicit instrumentation.
> 
> Reported-by: k2ci <kernel-bot@...inos.cn>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Genjian Zhang <zhanggenjian@...inos.cn>

Apologies for the delay, but finally queued, thank you!  Frederic gave
his ack off-list, which I have included in the wordsmithed version below.
Could you please check to make sure that I did not mess anything up?

							Thanx, Paul

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

commit 936acd859f4a7b2b0f9900e26bc972385286df6e
Author: Genjian Zhang <zhanggenjian@...inos.cn>
Date:   Thu Nov 10 16:24:43 2022 +0800

    context_tracking: Use arch_atomic_*() in __ct_user_enter and __ct_user_exit
    
    The following diagnostics are issued by objtool:
    
    vmlinux.o: warning: objtool: __ct_user_enter+0x45: call to
    __kasan_check_write() leaves .noinstr.text section
    vmlinux.o: warning: objtool: __ct_user_exit+0x3f: call to
    __kasan_check_write() leaves .noinstr.text section
    
    The reason for these diagnostics is that code marked noinstr if prohibited
    from using atomic_*() functions, which have explicit instrumentation.
    Therefore, switch to arch_ prefixed atomic operation functions to avoid
    the explicit instrumentation.
    
    Reported-by: k2ci <kernel-bot@...inos.cn>
    Reported-by: kernel test robot <lkp@...el.com>
    Signed-off-by: Genjian Zhang <zhanggenjian@...inos.cn>
    Acked-by: Frederic Weisbecker <frederic@...nel.org>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 77978e3723771..a09f1c19336ae 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -510,7 +510,7 @@ void noinstr __ct_user_enter(enum ctx_state state)
 			 * In this we case we don't care about any concurrency/ordering.
 			 */
 			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE))
-				atomic_set(&ct->state, state);
+				arch_atomic_set(&ct->state, state);
 		} else {
 			/*
 			 * Even if context tracking is disabled on this CPU, because it's outside
@@ -527,7 +527,7 @@ void noinstr __ct_user_enter(enum ctx_state state)
 			 */
 			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
 				/* Tracking for vtime only, no concurrent RCU EQS accounting */
-				atomic_set(&ct->state, state);
+				arch_atomic_set(&ct->state, state);
 			} else {
 				/*
 				 * Tracking for vtime and RCU EQS. Make sure we don't race
@@ -535,7 +535,7 @@ void noinstr __ct_user_enter(enum ctx_state state)
 				 * RCU only requires RCU_DYNTICKS_IDX increments to be fully
 				 * ordered.
 				 */
-				atomic_add(state, &ct->state);
+				arch_atomic_add(state, &ct->state);
 			}
 		}
 	}
@@ -630,12 +630,12 @@ void noinstr __ct_user_exit(enum ctx_state state)
 			 * In this we case we don't care about any concurrency/ordering.
 			 */
 			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE))
-				atomic_set(&ct->state, CONTEXT_KERNEL);
+				arch_atomic_set(&ct->state, CONTEXT_KERNEL);
 
 		} else {
 			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
 				/* Tracking for vtime only, no concurrent RCU EQS accounting */
-				atomic_set(&ct->state, CONTEXT_KERNEL);
+				arch_atomic_set(&ct->state, CONTEXT_KERNEL);
 			} else {
 				/*
 				 * Tracking for vtime and RCU EQS. Make sure we don't race
@@ -643,7 +643,7 @@ void noinstr __ct_user_exit(enum ctx_state state)
 				 * RCU only requires RCU_DYNTICKS_IDX increments to be fully
 				 * ordered.
 				 */
-				atomic_sub(state, &ct->state);
+				arch_atomic_sub(state, &ct->state);
 			}
 		}
 	}