Commit a98b6094 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[PATCH] taskstats: don't use tasklist_lock 



Remove tasklist_lock from taskstats.c. find_task_by_pid() is rcu-safe.
->siglock allows us to traverse subthread without tasklist.

Q: delay accounting looks wrong to me.  If sub-thread has already called
taskstats_exit_send() but didn't call release_task(self) yet it will be
accounted twice.  The window is big.  No?

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent b8534d7b

kernel/taskstats.c

+24 −35
Original line number Diff line number Diff line
@@ -174,21 +174,19 @@ static void send_cpu_listeners(struct sk_buff *skb, unsigned int cpu) 
	up_write(&listeners->sem);

}



static int fill_pid(pid_t pid, struct task_struct *pidtsk,

static int fill_pid(pid_t pid, struct task_struct *tsk,

		struct taskstats *stats)

{

	int rc = 0;

	struct task_struct *tsk = pidtsk;



	if (!pidtsk) {

		read_lock(&tasklist_lock);

		tsk = find_task_by_pid(pid);

	if (!tsk) {

			read_unlock(&tasklist_lock);

			return -ESRCH;

		}

		rcu_read_lock();

		tsk = find_task_by_pid(pid);

		if (tsk)

			get_task_struct(tsk);

		read_unlock(&tasklist_lock);

		rcu_read_unlock();

		if (!tsk)

			return -ESRCH;

	} else

		get_task_struct(tsk);
@@ -214,40 +212,28 @@ static int fill_pid(pid_t pid, struct task_struct *pidtsk, 


}



static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk,

static int fill_tgid(pid_t tgid, struct task_struct *first,

		struct taskstats *stats)

{

	struct task_struct *tsk, *first;

	struct task_struct *tsk;

	unsigned long flags;

	int rc = -ESRCH;



	/*

	 * Add additional stats from live tasks except zombie thread group

	 * leaders who are already counted with the dead tasks

	 */

	first = tgidtsk;

	if (!first) {

		read_lock(&tasklist_lock);

	rcu_read_lock();

	if (!first)

		first = find_task_by_pid(tgid);

		if (!first) {

			read_unlock(&tasklist_lock);

			return -ESRCH;

		}

		get_task_struct(first);

		read_unlock(&tasklist_lock);

	} else

		get_task_struct(first);



	if (!first || !lock_task_sighand(first, &flags))

		goto out;



	tsk = first;

	read_lock(&tasklist_lock);

	/* Start with stats from dead tasks */

	if (first->sighand) {

		spin_lock_irqsave(&first->sighand->siglock, flags);

	if (first->signal->stats)

		memcpy(stats, first->signal->stats, sizeof(*stats));

		spin_unlock_irqrestore(&first->sighand->siglock, flags);

	}



	tsk = first;

	do {

		if (tsk->exit_state == EXIT_ZOMBIE && thread_group_leader(tsk))

			continue;
@@ -260,15 +246,18 @@ static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk, 
		delayacct_add_tsk(stats, tsk);



	} while_each_thread(first, tsk);

	read_unlock(&tasklist_lock);

	stats->version = TASKSTATS_VERSION;



	unlock_task_sighand(first, &flags);

	rc = 0;

out:

	rcu_read_unlock();



	stats->version = TASKSTATS_VERSION;

	/*

	 * Accounting subsytems can also add calls here to modify

	 * fields of taskstats.

	 */

	put_task_struct(first);

	return 0;

	return rc;

}

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