Commit a593d6ed authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] proc: convert do_task_stat() to use lock_task_sighand() 



Drop tasklist_lock. ->siglock protects almost all interesting data
(including sub-threads traversal) except:

	->signal->tty
		protected by tty_mutex

	->real_parent
		the task can't be unhashed while we are holding
		->siglock, so ->real_parent can change from under us
		but we can safely dereference it under rcu_read_lock()

	->pgrp/->session
		we can get inconsistent numbers if the task does
		sys_setsid/daemonize at the same time. I hope this
		is acceptable.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5e6b3f42

fs/proc/array.c

+35 −28
Original line number Diff line number Diff line
@@ -321,7 +321,7 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole) 
	sigset_t sigign, sigcatch;

	char state;

	int res;

 	pid_t ppid, pgid = -1, sid = -1;

 	pid_t ppid = 0, pgid = -1, sid = -1;

	int num_threads = 0;

	struct mm_struct *mm;

	unsigned long long start_time;
@@ -329,8 +329,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole) 
	unsigned long  min_flt = 0,  maj_flt = 0;

	cputime_t cutime, cstime, utime, stime;

	unsigned long rsslim = 0;

	struct task_struct *t;

	char tcomm[sizeof(task->comm)];

	unsigned long flags;



	state = *get_task_state(task);

	vsize = eip = esp = 0;
@@ -348,15 +348,33 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole) 
	cutime = cstime = utime = stime = cputime_zero;



	mutex_lock(&tty_mutex);

	read_lock(&tasklist_lock);

	if (task->sighand) {

		spin_lock_irq(&task->sighand->siglock);

		num_threads = atomic_read(&task->signal->count);

	rcu_read_lock();

	if (lock_task_sighand(task, &flags)) {

		struct signal_struct *sig = task->signal;

		struct tty_struct *tty = sig->tty;



		if (tty) {

			/*

			 * sig->tty is not stable, but tty_mutex

			 * protects us from release_dev(tty)

			 */

			barrier();

			tty_pgrp = tty->pgrp;

			tty_nr = new_encode_dev(tty_devnum(tty));

		}



		num_threads = atomic_read(&sig->count);

		collect_sigign_sigcatch(task, &sigign, &sigcatch);



		cmin_flt = sig->cmin_flt;

		cmaj_flt = sig->cmaj_flt;

		cutime = sig->cutime;

		cstime = sig->cstime;

		rsslim = sig->rlim[RLIMIT_RSS].rlim_cur;



		/* add up live thread stats at the group level */

		if (whole) {

			t = task;

			struct task_struct *t = task;

			do {

				min_flt += t->min_flt;

				maj_flt += t->maj_flt;
@@ -364,31 +382,20 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole) 
				stime = cputime_add(stime, t->stime);

				t = next_thread(t);

			} while (t != task);

		}



		spin_unlock_irq(&task->sighand->siglock);

	}

	if (task->signal) {

		if (task->signal->tty) {

			tty_pgrp = task->signal->tty->pgrp;

			tty_nr = new_encode_dev(tty_devnum(task->signal->tty));

			min_flt += sig->min_flt;

			maj_flt += sig->maj_flt;

			utime = cputime_add(utime, sig->utime);

			stime = cputime_add(stime, sig->stime);

		}



		sid = sig->session;

		pgid = process_group(task);

		sid = task->signal->session;

		cmin_flt = task->signal->cmin_flt;

		cmaj_flt = task->signal->cmaj_flt;

		cutime = task->signal->cutime;

		cstime = task->signal->cstime;

		rsslim = task->signal->rlim[RLIMIT_RSS].rlim_cur;

		if (whole) {

			min_flt += task->signal->min_flt;

			maj_flt += task->signal->maj_flt;

			utime = cputime_add(utime, task->signal->utime);

			stime = cputime_add(stime, task->signal->stime);

		}

		ppid = rcu_dereference(task->real_parent)->tgid;



		unlock_task_sighand(task, &flags);

	}

	ppid = pid_alive(task) ? task->group_leader->real_parent->tgid : 0;

	read_unlock(&tasklist_lock);

	rcu_read_unlock();

	mutex_unlock(&tty_mutex);



	if (!whole || num_threads<2)

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