first_tid:
/* If nr exceeds the number of threads there is nothing todo */
if (nr) {
if (nr >= get_nr_threads(leader))
goto done;
}
This is not reliable: sub-threads can exit after this check, so the
'for' loop below can overlap and proc_task_readdir() can return an
already filldir'ed dirents.
for (; pos && pid_alive(pos); pos = next_thread(pos)) {
if (--nr > 0)
continue;
Off-by-one error, will return 'leader' when nr == 1.
This patch tries to fix these problems and simplify the code.
Signed-off-by: Oleg Nesterov <[email protected]>
--- MM/fs/proc/base.c~ 2006-03-19 23:25:38.000000000 +0300
+++ MM/fs/proc/base.c 2006-03-20 00:01:12.000000000 +0300
@@ -2180,38 +2180,29 @@ int proc_pid_readdir(struct file * filp,
static struct task_struct *first_tid(struct task_struct *leader,
int tid, int nr)
{
- struct task_struct *pos = NULL;
+ struct task_struct *pos;
rcu_read_lock();
/* Attempt to start with the pid of a thread */
- if (tid && (nr > 0)) {
- pos = find_task_by_pid(tid);
- if (pos && (pos->group_leader != leader))
- pos = NULL;
- if (pos)
- nr = 0;
- }
-
- /* If nr exceeds the number of threads there is nothing todo */
- if (nr) {
- if (nr >= get_nr_threads(leader))
- goto done;
- }
-
- /* If we haven't found our starting place yet start with the
- * leader and walk nr threads forward.
- */
- if (!pos && (nr >= 0))
- pos = leader;
-
- for (; pos && pid_alive(pos); pos = next_thread(pos)) {
- if (--nr > 0)
- continue;
- get_task_struct(pos);
- goto done;
- }
- pos = NULL;
-done:
+ if (tid && (nr > 0)) {
+ pos = find_task_by_pid(tid);
+ if (pos && (pos->group_leader == leader))
+ goto found;
+ }
+
+ /* If we haven't found our starting place yet start
+ * with the leader and walk nr threads forward.
+ */
+ for (pos = leader; nr > 0; --nr) {
+ pos = next_thread(pos);
+ if (pos == leader) {
+ pos = NULL;
+ goto out;
+ }
+ }
+found:
+ get_task_struct(pos);
+out:
rcu_read_unlock();
return pos;
}
-
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