linux-kernel - Re: [PATCH V3] riscv: patch_text: Fixup last cpu should be master

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Date:   Sun, 24 Apr 2022 15:33:57 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Masami Hiramatsu <mhiramat@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH V3] riscv: patch_text: Fixup last cpu should be master

On Sat, Apr 23, 2022 at 12:02 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>
> On Thu, 21 Apr 2022 15:57:32 PDT (-0700), Palmer Dabbelt wrote:
> > On Wed, 06 Apr 2022 07:16:49 PDT (-0700), 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>
> >> Acked-by: Palmer Dabbelt <palmer@...osinc.com>
> >> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> >> Cc: <stable@...r.kernel.org>
> >> ---
> >>  arch/riscv/kernel/patch.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> 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));
> >
> > Thanks, this is on fixes.
>
> Sorry, I forgot to add the Fixes and stable tags.  I just fixed that up,
> but I'm going to hold off on this one until next week's PR to make sure
> it has time to go through linux-next.

https://lore.kernel.org/linux-riscv/20220407073323.743224-3-guoren@kernel.org/

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/