Re: [PATCH] kdb: use ktime_get_seconds() instead of ktime_get_ts()

[Arnd Bergmann]

On Fri, Jan 26, 2018 at 4:03 AM, Baolin Wang <baolin.wang@xxxxxxxxxx> 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.
>
> Since kdb is only interested in the second field, we can use the
> ktime_get_seconds() to get the monotonic time without a lock,
> moreover we can remove the 'struct timespec', which is not y2038
> safe.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
> ---
>  kernel/debug/kdb/kdb_main.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 69e70f4..f0fc6f7 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2486,10 +2486,8 @@ static int kdb_kill(int argc, const char **argv)
>   */
>  static void kdb_sysinfo(struct sysinfo *val)
>  {
> -       struct timespec uptime;
> -       ktime_get_ts(&uptime);
>         memset(val, 0, sizeof(*val));
> -       val->uptime = uptime.tv_sec;
> +       val->uptime = ktime_get_seconds();
>         val->loads[0] = avenrun[0];
>         val->loads[1] = avenrun[1];
>         val->loads[2] = avenrun[2];

Using ktime_get_seconds() avoids locking problems, but I wonder what
would happen if we trigger the 'WARN_ON(timekeeping_suspended)'
from kdb. Is that a problem? If it is, we have to use ktime_get_mono_fast_ns()
and div_u64() instead.

       Arnd