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

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Date:   Sat, 12 Mar 2022 15:56:48 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Guo Ren <guoren@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>, linux-csky@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Chris Zankel <chris@...kel.net>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH] arch: patch_text: Fixup last cpu should be master

On Sat, Mar 12, 2022 at 7:56 AM <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 origin idea is that when
> the master CPU patch_text, others should wait for it. But current
> implementation is using the first CPU as master, which couldn't
> guarantee continue CPUs are waiting. This patch changes the last
> CPU as the master to solve the potaintial risk.
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> 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: Max Filippov <jcmvbkbc@...il.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> ---
>  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..6cfea9650e65 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() - 1)) {

atomic_inc_return returns the incremented value, so the last CPU gets
num_online_cpus(), not (num_online_cpus() - 1).

>                 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..19821a06a991 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() - 1)) {

Ditto.

>                 *(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..cca72a9388e3 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() - 1)) {

Ditto.

>                 ret =
>                     patch_text_nosync(patch->addr, &patch->insn,
>                                             GET_INSN_LENGTH(patch->insn));
> diff --git a/arch/xtensa/kernel/jump_label.c b/arch/xtensa/kernel/jump_label.c
> index 61cf6497a646..7e1d3f952eb3 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() - 1)) {

Ditto.

>                 local_patch_text(patch->addr, patch->data, patch->sz);
>                 atomic_inc(&patch->cpu_count);
>         } else {
> --
> 2.25.1
>


-- 
Thanks.
-- Max