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

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Message-ID: <27bff7e4-e25d-69bd-8a3c-1c100c7093f8@gmail.com>
Date:	Fri, 29 Jul 2016 08:07:54 -0600
From:	David Ahern <dsahern@...il.com>
To:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>,
	linux-kernel@...r.kernel.org
Cc:	ltc-kernel@...ml.intra.hitachi.co.jp,
	masumi.moritani.ju@...achi.com, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v3] perf sched: fix wrong conversion of task state

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@...achi.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  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")