From 05eeae208d08a05a6980cf2ff61f02843c0955fd Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Sat, 25 Mar 2006 03:07:48 -0800 Subject: [PATCH] [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kthread.c | 2 ++ mm/vmscan.c | 2 ++ 2 files changed, 4 insertions(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 6a5373868a98..c5f3c6613b6d 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -115,7 +115,9 @@ static void keventd_create_kthread(void *_create) 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); } diff --git a/mm/vmscan.c b/mm/vmscan.c index fd572bbdc9f5..78865c849f8f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1356,7 +1356,9 @@ static int __init kswapd_init(void) 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); -- 2.30.2