[PATCH] find_task_by_pid() needs tasklist_lock
A couple of places are forgetting to take it.
The kswapd case is probably unimportant. keventd_create_kthread() was racy.
The whole thing is a bit flakey: you start a kernel thread, get its pid from
kernel_thread() then look up its task_struct.
a) It assumes that pid recycling takes a "long" time.
b) We get a task_struct but no reference was taken on it. The owner of the
kswapd and kthread task_struct*'s must assume that the new thread won't
exit unexpectedly. Because if it does, they're left holding dead memory
and any attempt to control or stop that task will crash.
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 6a53738..c5f3c66 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -115,7 +115,9 @@
create->result = ERR_PTR(pid);
} else {
wait_for_completion(&create->started);
+ read_lock(&tasklist_lock);
create->result = find_task_by_pid(pid);
+ read_unlock(&tasklist_lock);
}
complete(&create->done);
}