[PATCH 1/3] proc: cleanup/simplify get_task_state/task_state_array

From: Oleg Nesterov
Date: Wed Nov 13 2013 - 09:35:54 EST


get_task_state() and task_state_array[] look confusing and
suboptimal, it is not clear what it can actually report to
user-space and task_state_array[] blows .data for no reason.

1. state = (tsk->state & TASK_REPORT) | tsk->exit_state is not
clear. TASK_REPORT is self-documenting but it is not clear
what ->exit_state can add.

Move the potential exit_state's (EXIT_ZOMBIE and EXIT_DEAD)
into TASK_REPORT and use it to calculate the final result.

2. With the change above it is obvious that task_state_array[]
has the unused entries just to make BUILD_BUG_ON() happy.

Change this BUILD_BUG_ON() to use TASK_REPORT rather than
TASK_STATE_MAX and shrink task_state_array[].

3. Turn the "while (state)" loop into fls(state).

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
fs/proc/array.c | 15 +++------------
include/linux/sched.h | 2 +-
2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index cbd0f1b..c995807 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -140,24 +140,15 @@ static const char * const task_state_array[] = {
"t (tracing stop)", /* 8 */
"Z (zombie)", /* 16 */
"X (dead)", /* 32 */
- "x (dead)", /* 64 */
- "K (wakekill)", /* 128 */
- "W (waking)", /* 256 */
- "P (parked)", /* 512 */
};

static inline const char *get_task_state(struct task_struct *tsk)
{
- unsigned int state = (tsk->state & TASK_REPORT) | tsk->exit_state;
- const char * const *p = &task_state_array[0];
+ unsigned int state = (tsk->state | tsk->exit_state) & TASK_REPORT;

- BUILD_BUG_ON(1 + ilog2(TASK_STATE_MAX) != ARRAY_SIZE(task_state_array));
+ BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != ARRAY_SIZE(task_state_array)-1);

- while (state) {
- p++;
- state >>= 1;
- }
- return *p;
+ return task_state_array[fls(state)];
}

static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e27baee..ee2c2e6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -163,7 +163,7 @@ extern char ___assert_task_state[1 - 2*!!(
/* get_task_state() */
#define TASK_REPORT (TASK_RUNNING | TASK_INTERRUPTIBLE | \
TASK_UNINTERRUPTIBLE | __TASK_STOPPED | \
- __TASK_TRACED)
+ __TASK_TRACED | EXIT_ZOMBIE | EXIT_DEAD)

#define task_is_traced(task) ((task->state & __TASK_TRACED) != 0)
#define task_is_stopped(task) ((task->state & __TASK_STOPPED) != 0)
--
1.5.5.1

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