From: Guo Ren <guoren@linux.alibaba.com>

These patch_text implementations are using stop_machine_cpuslocked
infrastructure with atomic cpu_count. The original idea: When the
master CPU patch_text, the others should wait for it. But current
implementation is using the first CPU as master, which couldn't
guarantee the remaining CPUs are waiting. This patch changes the
last CPU as the master to solve the potential risk.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: <stable@vger.kernel.org>
---
 arch/xtensa/kernel/jump_label.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/xtensa/kernel/jump_label.c b/arch/xtensa/kernel/jump_label.c
index 0dde21e0d3de..ad1841cecdfb 100644
--- a/arch/xtensa/kernel/jump_label.c
+++ b/arch/xtensa/kernel/jump_label.c
@@ -40,7 +40,7 @@ static int patch_text_stop_machine(void *data)
 {
 	struct patch *patch = data;
 
-	if (atomic_inc_return(&patch->cpu_count) == 1) {
+	if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
 		local_patch_text(patch->addr, patch->data, patch->sz);
 		atomic_inc(&patch->cpu_count);
 	} else {
-- 
2.25.1

On Wed, Apr 6, 2022 at 7:28 AM <guoren@kernel.org> wrote:
>
> From: Guo Ren <guoren@linux.alibaba.com>
>
> These patch_text implementations are using stop_machine_cpuslocked
> infrastructure with atomic cpu_count. The original idea: When the
> master CPU patch_text, the others should wait for it. But current
> implementation is using the first CPU as master, which couldn't
> guarantee the remaining CPUs are waiting. This patch changes the
> last CPU as the master to solve the potential risk.
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: <stable@vger.kernel.org>
> ---
>  arch/xtensa/kernel/jump_label.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks. Applied to my xtensa tree.

-- Max

On Thu, Apr 7, 2022 at 11:35 AM Max Filippov <jcmvbkbc@gmail.com> wrote:
>
> On Wed, Apr 6, 2022 at 7:28 AM <guoren@kernel.org> wrote:
> >
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > These patch_text implementations are using stop_machine_cpuslocked
> > infrastructure with atomic cpu_count. The original idea: When the
> > master CPU patch_text, the others should wait for it. But current
> > implementation is using the first CPU as master, which couldn't
> > guarantee the remaining CPUs are waiting. This patch changes the
> > last CPU as the master to solve the potential risk.
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
> > Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
> > Cc: <stable@vger.kernel.org>
> > ---
> >  arch/xtensa/kernel/jump_label.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Thanks. Applied to my xtensa tree.
I've missed the "Fixes:" for stable@vger.kernel.org, so I would update
v3 to fix it.

>
> -- Max



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/