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[PATCH] find_task_by_pid() needs tasklist_lock

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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>
This commit is contained in:
Andrew Morton 2006-03-25 03:07:48 -08:00 committed by Linus Torvalds
parent c1f5a19446
commit 05eeae208d
2 changed files with 4 additions and 0 deletions
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2
kernel/kthread.c
View File

@ -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);
}

2
mm/vmscan.c
View File

@ -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);