Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220712021527.109921-1-lihuafei1@huawei.com> <20220712021527.109921-3-lihuafei1@huawei.com>
In-Reply-To: <20220712021527.109921-3-lihuafei1@huawei.com>
From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Mon, 18 Jul 2022 11:01:33 +0200
Message-ID: <CACRpkdY0Jo7rzXjc10dLLrHnDkoBphvNYiyF5q8iHz-8QqaEwA@mail.gmail.com>
Subject: Re: [PATCH 2/5] ARM: stacktrace: Avoid duplicate saving of exception
 PC value
To:     Li Huafei <lihuafei1@huawei.com>
Cc:     linux@armlinux.org.uk, rmk+kernel@armlinux.org.uk, ardb@kernel.org,
        will@kernel.org, mark.rutland@arm.com, broonie@kernel.org,
        peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
        alexander.shishkin@linux.intel.com, jolsa@kernel.org,
        namhyung@kernel.org, arnd@arndb.de, rostedt@goodmis.org,
        nick.hawkins@hpe.com, john@phrozen.org, mhiramat@kernel.org,
        ast@kernel.org, linyujun809@huawei.com, ndesaulniers@google.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, Jul 12, 2022 at 4:18 AM Li Huafei <lihuafei1@huawei.com> wrote:

> Because an exception stack frame is not created in the exception entry,
> save_trace() does special handling for the exception PC, but this is
> only needed when CONFIG_FRAME_POINTER_UNWIND=y. When
> CONFIG_ARM_UNWIND=y, unwind annotations have been added to the exception
> entry and save_trace() will repeatedly save the exception PC:
>
>     [0x7f000090] hrtimer_hander+0x8/0x10 [hrtimer]
>     [0x8019ec50] __hrtimer_run_queues+0x18c/0x394
>     [0x8019f760] hrtimer_run_queues+0xbc/0xd0
>     [0x8019def0] update_process_times+0x34/0x80
>     [0x801ad2a4] tick_periodic+0x48/0xd0
>     [0x801ad3dc] tick_handle_periodic+0x1c/0x7c
>     [0x8010f2e0] twd_handler+0x30/0x40
>     [0x80177620] handle_percpu_devid_irq+0xa0/0x23c
>     [0x801718d0] generic_handle_domain_irq+0x24/0x34
>     [0x80502d28] gic_handle_irq+0x74/0x88
>     [0x8085817c] generic_handle_arch_irq+0x58/0x78
>     [0x80100ba8] __irq_svc+0x88/0xc8
>     [0x80108114] arch_cpu_idle+0x38/0x3c
>     [0x80108114] arch_cpu_idle+0x38/0x3c    <==== duplicate saved exception PC
>     [0x80861bf8] default_idle_call+0x38/0x130
>     [0x8015d5cc] do_idle+0x150/0x214
>     [0x8015d978] cpu_startup_entry+0x18/0x1c
>     [0x808589c0] rest_init+0xd8/0xdc
>     [0x80c00a44] arch_post_acpi_subsys_init+0x0/0x8
>
> We can move the special handling of the exception PC in save_trace() to
> the unwind_frame() of the frame pointer unwinder.
>
> Signed-off-by: Li Huafei <lihuafei1@huawei.com>

This is another very nice patch!
Reviewed-by: Linus Waleij <linus.walleij@linaro.org>

Nitpick:

> +               if ((unsigned long)&regs[1] > ALIGN(frame->sp, THREAD_SIZE))
> +                       return -EINVAL;

It'd be nice to add a comment saying what is in regs[1] at this point
so it is easier to understand the code. Not your fault as it is just
moved code, but if you have time please add a small comment.

Yours,
Linus Walleij