Message-ID: <CAJF2gTR6Pd3nVKt9e=rdMynBV0-EOmy5ZbndduEJiQLLe6vdpA@mail.gmail.com>
Date:   Mon, 21 Mar 2022 07:49:09 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Chris Zankel <chris@...kel.net>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH V2] arch: patch_text: Fixup last cpu should be master

On Mon, Mar 21, 2022 at 2:05 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>
> 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 Okay with split patches, @Arnd Bergmann what's your opinion?
We've got all arch vendors' agreements (arm64, csky, riscv, xtensa).

>
> 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.
Arnd has given some comments on unnecessary #error, maybe I need to update V2.

>
> > 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 {



-- 
Best Regards
 Guo Ren

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

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