linux-kernel - Re: [PATCH V2] arch: patch_text: Fixup last cpu should be master

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Date:   Sun, 20 Mar 2022 11:05:17 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     guoren@...nel.org
CC:     guoren@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        guoren@...ux.alibaba.com, jcmvbkbc@...il.com,
        Will Deacon <will@...nel.org>, catalin.marinas@....com,
        mhiramat@...nel.org, chris@...kel.net,
        Arnd Bergmann <arnd@...db.de>
Subject:     Re: [PATCH V2] arch: patch_text: Fixup last cpu should be master

On Sat, 12 Mar 2022 17:22:21 PST (-0800), guoren@...nel.org wrote:
> 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.
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Reviewed-by: Max Filippov <jcmvbkbc@...il.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Peter Zijlstra <peterz@...radead.org
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Chris Zankel <chris@...kel.net>
> Cc: Arnd Bergmann <arnd@...db.de>
>
> ---
> Changes in V2:
>  - Fixup last cpu should be num_online_cpus() by Max Filippov
>  - Fixup typos found by Max Filippov
> ---
>  arch/arm64/kernel/patching.c      | 4 ++--
>  arch/csky/kernel/probes/kprobes.c | 2 +-
>  arch/riscv/kernel/patch.c         | 2 +-
>  arch/xtensa/kernel/jump_label.c   | 2 +-
>  4 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
> index 771f543464e0..33e0fabc0b79 100644
> --- a/arch/arm64/kernel/patching.c
> +++ b/arch/arm64/kernel/patching.c
> @@ -117,8 +117,8 @@ static int __kprobes aarch64_insn_patch_text_cb(void *arg)
>  	int i, ret = 0;
>  	struct aarch64_insn_patch *pp = arg;
>
> -	/* The first CPU becomes master */
> -	if (atomic_inc_return(&pp->cpu_count) == 1) {
> +	/* The last CPU becomes master */
> +	if (atomic_inc_return(&pp->cpu_count) == num_online_cpus()) {
>  		for (i = 0; ret == 0 && i < pp->insn_cnt; i++)
>  			ret = aarch64_insn_patch_text_nosync(pp->text_addrs[i],
>  							     pp->new_insns[i]);
> diff --git a/arch/csky/kernel/probes/kprobes.c b/arch/csky/kernel/probes/kprobes.c
> index 42920f25e73c..34ba684d5962 100644
> --- a/arch/csky/kernel/probes/kprobes.c
> +++ b/arch/csky/kernel/probes/kprobes.c
> @@ -30,7 +30,7 @@ static int __kprobes patch_text_cb(void *priv)
>  	struct csky_insn_patch *param = priv;
>  	unsigned int addr = (unsigned int)param->addr;
>
> -	if (atomic_inc_return(&param->cpu_count) == 1) {
> +	if (atomic_inc_return(&param->cpu_count) == num_online_cpus()) {
>  		*(u16 *) addr = cpu_to_le16(param->opcode);
>  		dcache_wb_range(addr, addr + 2);
>  		atomic_inc(&param->cpu_count);
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 0b552873a577..765004b60513 100644
> --- 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));

Acked-by: Palmer Dabbelt <palmer@...osinc.com> # RISC-V

It's better if these sorts of things get split up: there's really no 
dependency between these diffs and having them together just makes for a 
merge/test headache for everyone.

I'm OK taking this through the RISC-V tree if other folks ack it, but 
for now I'm going to assume it's going to go in via somewhere else.

> diff --git a/arch/xtensa/kernel/jump_label.c b/arch/xtensa/kernel/jump_label.c
> index 61cf6497a646..b67efcd7e32c 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 {