linux-kernel - Re: [PATCH v2] kdb: use ktime_get_mono_fast_ns() instead of ktime_get

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Date:   Tue, 30 Jan 2018 09:48:41 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     jason.wessel@...driver.com, mingo@...nel.org, arnd@...db.de,
        broonie@...nel.org, kgdb-bugreport@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kdb: use ktime_get_mono_fast_ns() instead of
 ktime_get_ts()

On Mon, Jan 29, 2018 at 10:22:51AM +0800, Baolin Wang wrote:
> The kdb code will print the monotonic time by ktime_get_ts(), but
> the ktime_get_ts() will be protected by a sequence lock, that will
> introduce one deadlock risk if the lock was already held in the
> context from which we entered the debugger.
> 
> Thus we can use the ktime_get_mono_fast_ns() to get the monotonic
> time, which is NMI safe access to clock monotonic. Moreover we can
> remove the 'struct timespec', which is not y2038 safe.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>


> ---
> Changes since v1:
>  - Use ktime_get_mono_fast_ns() instead of ktime_get_seconds().
> ---
>  kernel/debug/kdb/kdb_main.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 69e70f4..bf1d0e0 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2486,10 +2486,10 @@ static int kdb_kill(int argc, const char **argv)
>   */
>  static void kdb_sysinfo(struct sysinfo *val)
>  {
> -	struct timespec uptime;
> -	ktime_get_ts(&uptime);
> +	u64 uptime = ktime_get_mono_fast_ns();
> +
>  	memset(val, 0, sizeof(*val));
> -	val->uptime = uptime.tv_sec;
> +	val->uptime = div_u64(uptime, NSEC_PER_SEC);
>  	val->loads[0] = avenrun[0];
>  	val->loads[1] = avenrun[1];
>  	val->loads[2] = avenrun[2];
> -- 
> 1.7.9.5
>