With CONFIG_PREEMPT_RCU read_lock(tasklist_lock) doesn't imply rcu_read_lock(),
but find_pid_ns()->hlist_for_each_entry_rcu() should be safe under tasklist.
Usually it is, detach_pid() is always called under write_lock(tasklist_lock),
but copy_process() calls free_pid() lockless.
"#ifdef CONFIG_PREEMPT_RCU" is added mostly as documentation, perhaps it is
too ugly and should be removed.
Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
--- MM/kernel/fork.c~PR_RCU 2008-01-27 17:09:47.000000000 +0300
+++ MM/kernel/fork.c 2008-01-29 19:23:44.000000000 +0300
@@ -1335,8 +1335,19 @@ static struct task_struct *copy_process(
return p;
bad_fork_free_pid:
- if (pid != &init_struct_pid)
+ if (pid != &init_struct_pid) {
+#ifdef CONFIG_PREEMPT_RCU
+ /*
+ * read_lock(tasklist_lock) doesn't imply rcu_read_lock(),
+ * make sure find_pid() is safe under read_lock(tasklist).
+ */
+ write_lock_irq(&tasklist_lock);
+#endif
free_pid(pid);
+#ifdef CONFIG_PREEMPT_RCU
+ write_unlock_irq(&tasklist_lock);
+#endif
+ }
bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
bad_fork_cleanup_keys:
--
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