linux-kernel - [PATCH 1/3] xtensa: patch_text: Fixup last cpu should be master

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Date:   Tue, 19 Apr 2022 23:16:09 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        Chris Zankel <chris@...kel.net>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Guo Ren <guoren@...nel.org>, Max Filippov <jcmvbkbc@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>, stable@...r.kernel.org
Subject: [PATCH 1/3] xtensa: patch_text: Fixup last cpu should be master

From: Guo Ren <guoren@...ux.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.

Fixes: 64711f9a47d4 ("xtensa: implement jump_label support")
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Reviewed-by: Max Filippov <jcmvbkbc@...il.com>
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: <stable@...r.kernel.org>
Message-Id: <20220407073323.743224-4-guoren@...nel.org>
Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
 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 {
-- 
2.30.2