[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/mm/vmscan.c b/mm/vmscan.c
index fd572bb..78865c8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1356,7 +1356,9 @@
pid = kernel_thread(kswapd, pgdat, CLONE_KERNEL);
BUG_ON(pid < 0);
+ read_lock(&tasklist_lock);
pgdat->kswapd = find_task_by_pid(pid);
+ read_unlock(&tasklist_lock);
}
total_memory = nr_free_pagecache_pages();
hotcpu_notifier(cpu_callback, 0);