linux-kernel - [PATCH 5.15 041/177] riscv: patch_text: Fixup last cpu should be master

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Message-Id: <20220504153056.592587620@linuxfoundation.org>
Date:   Wed,  4 May 2022 18:43:54 +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>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH 5.15 041/177] riscv: patch_text: Fixup last cpu should be master

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

commit 8ec1442953c66a1d8462cccd8c20b7ba561f5915 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.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Acked-by: Palmer Dabbelt <palmer@...osinc.com>
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Fixes: 043cb41a85de ("riscv: introduce interfaces to patch kernel code")
Cc: stable@...r.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/riscv/kernel/patch.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -104,7 +104,7 @@ static int patch_text_cb(void *data)
 	struct patch_insn *patch = data;
 	int ret = 0;
 
-	if (atomic_inc_return(&patch->cpu_count) == 1) {
+	if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
 		ret =
 		    patch_text_nosync(patch->addr, &patch->insn,
 					    GET_INSN_LENGTH(patch->insn));