From 05eeae208d08a05a6980cf2ff61f02843c0955fd Mon Sep 17 00:00:00 2001
From: Andrew Morton <akpm@osdl.org>
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 <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
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);
--
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