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authorOleg Nesterov <oleg@tv-sign.ru>2008-07-25 04:47:31 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-25 13:53:38 -0400
commite4901f92a8dbe843e76651a50f7a2a6dd3d53474 (patch)
tree4cfd5edd17fcf1fe5e4372611c561928a99107d0 /fs
parent2b201a9eddf509e8e935b45e573648e36f4b623f (diff)
coredump: zap_threads: comments && use while_each_thread()
No changes in fs/exec.o The for_each_process() loop in zap_threads() is very subtle, it is not clear why we don't race with fork/exit/exec. Add the fat comment. Also, change the code to use while_each_thread(). Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c39
1 files changed, 32 insertions, 7 deletions
diff --git a/fs/exec.c b/fs/exec.c
index e41aef0fb351..af249af4ccab 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1517,7 +1517,7 @@ static void zap_process(struct task_struct *start)
1517 sigaddset(&t->pending.signal, SIGKILL); 1517 sigaddset(&t->pending.signal, SIGKILL);
1518 signal_wake_up(t, 1); 1518 signal_wake_up(t, 1);
1519 } 1519 }
1520 } while ((t = next_thread(t)) != start); 1520 } while_each_thread(start, t);
1521} 1521}
1522 1522
1523static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm, 1523static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
@@ -1539,7 +1539,36 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
1539 1539
1540 if (atomic_read(&mm->mm_users) == mm->core_waiters + 1) 1540 if (atomic_read(&mm->mm_users) == mm->core_waiters + 1)
1541 goto done; 1541 goto done;
1542 1542 /*
1543 * We should find and kill all tasks which use this mm, and we should
1544 * count them correctly into mm->core_waiters. We don't take tasklist
1545 * lock, but this is safe wrt:
1546 *
1547 * fork:
1548 * None of sub-threads can fork after zap_process(leader). All
1549 * processes which were created before this point should be
1550 * visible to zap_threads() because copy_process() adds the new
1551 * process to the tail of init_task.tasks list, and lock/unlock
1552 * of ->siglock provides a memory barrier.
1553 *
1554 * do_exit:
1555 * The caller holds mm->mmap_sem. This means that the task which
1556 * uses this mm can't pass exit_mm(), so it can't exit or clear
1557 * its ->mm.
1558 *
1559 * de_thread:
1560 * It does list_replace_rcu(&leader->tasks, &current->tasks),
1561 * we must see either old or new leader, this does not matter.
1562 * However, it can change p->sighand, so lock_task_sighand(p)
1563 * must be used. Since p->mm != NULL and we hold ->mmap_sem
1564 * it can't fail.
1565 *
1566 * Note also that "g" can be the old leader with ->mm == NULL
1567 * and already unhashed and thus removed from ->thread_group.
1568 * This is OK, __unhash_process()->list_del_rcu() does not
1569 * clear the ->next pointer, we will find the new leader via
1570 * next_thread().
1571 */
1543 rcu_read_lock(); 1572 rcu_read_lock();
1544 for_each_process(g) { 1573 for_each_process(g) {
1545 if (g == tsk->group_leader) 1574 if (g == tsk->group_leader)
@@ -1549,17 +1578,13 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
1549 do { 1578 do {
1550 if (p->mm) { 1579 if (p->mm) {
1551 if (p->mm == mm) { 1580 if (p->mm == mm) {
1552 /*
1553 * p->sighand can't disappear, but
1554 * may be changed by de_thread()
1555 */
1556 lock_task_sighand(p, &flags); 1581 lock_task_sighand(p, &flags);
1557 zap_process(p); 1582 zap_process(p);
1558 unlock_task_sighand(p, &flags); 1583 unlock_task_sighand(p, &flags);
1559 } 1584 }
1560 break; 1585 break;
1561 } 1586 }
1562 } while ((p = next_thread(p)) != g); 1587 } while_each_thread(g, p);
1563 } 1588 }
1564 rcu_read_unlock(); 1589 rcu_read_unlock();
1565done: 1590done: