riscv: patch_text: Fixup last cpu should be master

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@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 043cb41a85de ("riscv: introduce interfaces to patch kernel code")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 3fe7a5296aa5897c4867a019e66315c1dfbe5888..1612e11f7bf6d60c9011b78c521f7a7dc206209c 100644 (file)
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -100,7 +100,7 @@ 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));