[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: 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>
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 279fbf5..35bd39d 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -321,7 +321,7 @@
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 @@
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 @@
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 @@
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)