Re: [PATCH] context_tracking: Use arch_atomic_*() in __ct_user_enter and __ct_user_exit

From: Paul E. McKenney
Date: Fri Jan 06 2023 - 09:53:45 EST


On Thu, Nov 10, 2022 at 04:24:43PM +0800, Genjian wrote:
> From: Genjian Zhang <zhanggenjian@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Genjian Zhang <zhanggenjian@xxxxxxxxxx>

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@xxxxxxxxxx>
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@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Genjian Zhang <zhanggenjian@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

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);
}
}
}