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[PATCH] proc: convert do_task_stat() to use lock_task_sighand()

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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: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-10-02 02:18:53 -07:00 committed by Linus Torvalds
parent 5e6b3f42ed
commit a593d6edeb
1 changed files with 35 additions and 28 deletions
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63
fs/proc/array.c
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@ -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);
min_flt += sig->min_flt;
maj_flt += sig->maj_flt;
utime = cputime_add(utime, sig->utime);
stime = cputime_add(stime, sig->stime);
}
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));
}
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)