Re: [PATCH 6/6] sched: Change task_struct::state

Daniel Thompson
2021-06-07T10:45:06Z

On Wed, Jun 02, 2021 at 03:12:31PM +0200, Peter Zijlstra wrote:
> Change the type and name of task_struct::state. Drop the volatile and
> shrink it to an 'unsigned int'. Rename it in order to find all uses
> such that we can use READ_ONCE/WRITE_ONCE as appropriate.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> ...
> kernel/debug/kdb/kdb_support.c | 18 +++++++------
> ...
> --- a/kernel/debug/kdb/kdb_support.c
> +++ b/kernel/debug/kdb/kdb_support.c
> @@ -609,23 +609,25 @@ unsigned long kdb_task_state_string(cons
> */
> char kdb_task_state_char (const struct task_struct *p)
> {
> - int cpu;
> - char state;
> + unsigned int p_state;
> unsigned long tmp;
> + char state;
> + int cpu;
>
> if (!p ||
> copy_from_kernel_nofault(&tmp, (char *)p, sizeof(unsigned long)))
> return 'E';
>
> cpu = kdb_process_cpu(p);
> - state = (p->state == 0) ? 'R' :
> - (p->state < 0) ? 'U' :
> - (p->state & TASK_UNINTERRUPTIBLE) ? 'D' :
> - (p->state & TASK_STOPPED) ? 'T' :
> - (p->state & TASK_TRACED) ? 'C' :
> + p_state = READ_ONCE(p->__state);
> + state = (p_state == 0) ? 'R' :
> + (p_state < 0) ? 'U' :

Looks like the U here stands for Unreachable since this patch makes it
more obvious that this clause is (and previously was) exactly that!

Dropping the U state would be good since I guess this will show up as a
"new" warning in some tools. However it was a preexisting problem so with
or without this cleaned up:
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

Daniel.

> + (p_state & TASK_UNINTERRUPTIBLE) ? 'D' :
> + (p_state & TASK_STOPPED) ? 'T' :
> + (p_state & TASK_TRACED) ? 'C' :
> (p->exit_state & EXIT_ZOMBIE) ? 'Z' :
> (p->exit_state & EXIT_DEAD) ? 'E' :
> - (p->state & TASK_INTERRUPTIBLE) ? 'S' : '?';
> + (p_state & TASK_INTERRUPTIBLE) ? 'S' : '?';
> if (is_idle_task(p)) {
> /* Idle task. Is it really idle, apart from the kdb
> * interrupt? */