Re: [PATCH v3] perf sched: fix wrong conversion of task state

[David Ahern]

On 7/28/16 10:00 PM, Tomoki Sekiyama wrote:
> sched_out_state() converts the prev_state u64 bitmask to a char in
> a wrong way, which may cause invalid memory access.
> TASK_STATE_TO_CHAR_STR should also be fixed to adapt current
> kernel's sched.h.

Masami's point is that this should be 2 separate patches -- as suggested 
by the 'also' in the description.

> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@xxxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
>  tools/perf/builtin-sched.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 0dfe8df..5776263 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -70,7 +70,7 @@ struct sched_atom {
>  	struct task_desc	*wakee;
>  };
>
> -#define TASK_STATE_TO_CHAR_STR "RSDTtZXxKWP"
> +#define TASK_STATE_TO_CHAR_STR "RSDTtXZxKWPNn"

Patch 1 updates this macro to latest kernel version.

>  enum thread_state {
>  	THREAD_SLEEPING = 0,
> @@ -897,9 +897,10 @@ static int thread_atoms_insert(struct perf_sched *sched, struct thread *thread)
>
>  static char sched_out_state(u64 prev_state)
>  {
> -	const char *str = TASK_STATE_TO_CHAR_STR;
> +	const char str[] = TASK_STATE_TO_CHAR_STR;
> +	unsigned int bit = prev_state ? __ffs(prev_state) + 1 : 0;
>
> -	return str[prev_state];
> +	return bit < ARRAY_SIZE(str) - 1 ? str[bit] : '?';
>  }
>
>  static int

Patch 2 fixes access to str by treating prev_state as a bitmask and 
adding the Fixes:

Fixes: cdce9d738b91e ("perf sched: Add sched latency profiling")