linux-kernel - Re: [PATCH] watchdog: qcom: Avoid context switch in restart handler

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Message-ID: <c2ba5062-3274-e706-3e43-cb2ca6919154@roeck-us.net>
Date:   Sun, 6 Dec 2020 23:13:43 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        wim@...ux-watchdog.org
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: qcom: Avoid context switch in restart handler

On 12/6/20 10:00 PM, Manivannan Sadhasivam wrote:
> The use of msleep() in the restart handler will cause scheduler to
> induce a context switch which is not desirable. This generates below
> warning on SDX55 when WDT is the only available restart source:
> 
> [   39.800188] reboot: Restarting system
> [   39.804115] ------------[ cut here ]------------
> [   39.807855] WARNING: CPU: 0 PID: 678 at kernel/rcu/tree_plugin.h:297 rcu_note_context_switch+0x190/0x764
> [   39.812538] Modules linked in:
> [   39.821954] CPU: 0 PID: 678 Comm: reboot Not tainted 5.10.0-rc1-00063-g33a9990d1d66-dirty #47
> [   39.824854] Hardware name: Generic DT based system
> [   39.833470] [<c0310fbc>] (unwind_backtrace) from [<c030c544>] (show_stack+0x10/0x14)
> [   39.838154] [<c030c544>] (show_stack) from [<c0c218f0>] (dump_stack+0x8c/0xa0)
> [   39.846049] [<c0c218f0>] (dump_stack) from [<c0322f80>] (__warn+0xd8/0xf0)
> [   39.853058] [<c0322f80>] (__warn) from [<c0c1dc08>] (warn_slowpath_fmt+0x64/0xc8)
> [   39.859925] [<c0c1dc08>] (warn_slowpath_fmt) from [<c038b6f4>] (rcu_note_context_switch+0x190/0x764)
> [   39.867503] [<c038b6f4>] (rcu_note_context_switch) from [<c0c2aa3c>] (__schedule+0x84/0x640)
> [   39.876685] [<c0c2aa3c>] (__schedule) from [<c0c2b050>] (schedule+0x58/0x10c)
> [   39.885095] [<c0c2b050>] (schedule) from [<c0c2eed0>] (schedule_timeout+0x1e8/0x3d4)
> [   39.892135] [<c0c2eed0>] (schedule_timeout) from [<c039ad40>] (msleep+0x2c/0x38)
> [   39.899947] [<c039ad40>] (msleep) from [<c0a59d0c>] (qcom_wdt_restart+0xc4/0xcc)
> [   39.907319] [<c0a59d0c>] (qcom_wdt_restart) from [<c0a58290>] (watchdog_restart_notifier+0x18/0x28)
> [   39.914715] [<c0a58290>] (watchdog_restart_notifier) from [<c03468e0>] (atomic_notifier_call_chain+0x60/0x84)
> [   39.923487] [<c03468e0>] (atomic_notifier_call_chain) from [<c030ae64>] (machine_restart+0x78/0x7c)
> [   39.933551] [<c030ae64>] (machine_restart) from [<c0348048>] (__do_sys_reboot+0xdc/0x1e0)
> [   39.942397] [<c0348048>] (__do_sys_reboot) from [<c0300060>] (ret_fast_syscall+0x0/0x54)
> [   39.950721] Exception stack(0xc3e0bfa8 to 0xc3e0bff0)
> [   39.958855] bfa0:                   0001221c bed2fe24 fee1dead 28121969 01234567 00000000
> [   39.963832] bfc0: 0001221c bed2fe24 00000003 00000058 000225e0 00000000 00000000 00000000
> [   39.971985] bfe0: b6e62560 bed2fc84 00010fd8 b6e62580
> [   39.980124] ---[ end trace 3f578288bad866e4 ]---
> 
> Hence, replace msleep() with mdelay() to fix this issue.
> 
> Fixes: 05e487d905ab ("watchdog: qcom: register a restart notifier")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
>  drivers/watchdog/qcom-wdt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index ab7465d186fd..cdf754233e53 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -148,7 +148,7 @@ static int qcom_wdt_restart(struct watchdog_device *wdd, unsigned long action,
>  	 */
>  	wmb();
>  
> -	msleep(150);
> +	mdelay(150);
>  	return 0;
>  }
>  
>