linux-kernel - [PATCH 5.4 45/62] xtensa: patch_text: Fixup last cpu should be master

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Date:   Tue, 26 Apr 2022 10:21:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Guo Ren <guoren@...nel.org>, Max Filippov <jcmvbkbc@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH 5.4 45/62] xtensa: patch_text: Fixup last cpu should be master

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

commit ee69d4be8fd064cd08270b4808d2dfece3614ee0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/xtensa/kernel/jump_label.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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
 {
 	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 {