[PATCH] softirq: Replace this_cpu_write with __this_cpu_write if irq is disabled

[PATCH] softirq: Replace this_cpu_write with __this_cpu_write if irq is disabled

[Muchun Song]

Irq is disabled before this_cpu_write(), so we can Replace this_cpu_write()
with __this_cpu_write().

Signed-off-by: Muchun Song <smuchun@gmail.com>
---
 kernel/softirq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 2c3382378d94..eaf3bdf7c749 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -650,7 +650,7 @@ static int takeover_tasklets(unsigned int cpu)
 	/* Find end, append list for that CPU. */
 	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
-		this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
+		__this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 		per_cpu(tasklet_vec, cpu).head = NULL;
 		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 	}
-- 
2.17.1

[tip:irq/core] softirq: Use __this_cpu_write() in takeover_tasklets()

[tip-bot for Muchun Song]

Commit-ID:  8afecaa68df1e94a9d634f1f961533a925f239fc
Gitweb:     https://git.kernel.org/tip/8afecaa68df1e94a9d634f1f961533a925f239fc
Author:     Muchun Song <smuchun@gmail.com>
AuthorDate: Tue, 18 Jun 2019 22:33:05 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 23 Jun 2019 18:14:27 +0200

softirq: Use __this_cpu_write() in takeover_tasklets()

The code is executed with interrupts disabled, so it's safe to use
__this_cpu_write().

[ tglx: Massaged changelog ]

Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: joel@joelfernandes.org
Cc: rostedt@goodmis.org
Cc: frederic@kernel.org
Cc: paulmck@linux.vnet.ibm.com
Cc: alexander.levin@verizon.com
Cc: peterz@infradead.org
Link: https://lkml.kernel.org/r/20190618143305.2038-1-smuchun@gmail.com

---
 kernel/softirq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 2c3382378d94..eaf3bdf7c749 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -650,7 +650,7 @@ static int takeover_tasklets(unsigned int cpu)
 	/* Find end, append list for that CPU. */
 	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
 		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
-		this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
+		__this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
 		per_cpu(tasklet_vec, cpu).head = NULL;
 		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
 	}

Re: [PATCH] softirq: Replace this_cpu_write with __this_cpu_write if irq is disabled

[Paul E. McKenney]

On Tue, Jun 18, 2019 at 10:33:05PM +0800, Muchun Song wrote:
> Irq is disabled before this_cpu_write(), so we can Replace this_cpu_write()
> with __this_cpu_write().
> 
> Signed-off-by: Muchun Song <smuchun@gmail.com>

This passes light rcutorture testing, and looks rather low risk.

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

> ---
>  kernel/softirq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 2c3382378d94..eaf3bdf7c749 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -650,7 +650,7 @@ static int takeover_tasklets(unsigned int cpu)
>  	/* Find end, append list for that CPU. */
>  	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
>  		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
> -		this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
> +		__this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
>  		per_cpu(tasklet_vec, cpu).head = NULL;
>  		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
>  	}
> -- 
> 2.17.1
>