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From: WANG Cong <xiyou.wangcong@gmail.com>
Subject: Re: what is spinlock depth
Date: Tue, 1 Feb 2011 06:40:06 +0000 (UTC)
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On Mon, 31 Jan 2011 15:27:08 -0500, Sri Ram Vemulpali wrote:

> Hi all,
> 
> I am reading spinlock code and looking at struct raw_spinlock. I found
> struct lockdep_map as member.
...
> Can anyone help me explain, how this struct helps the spinlock. Why do
> we need lockdepth.

Here "lockdep" is short for Lock Dependence, not Lock Depth.

We do have lock depth things, e.g. ->lock_depth of struct task_struct,
which means the nested level of BKL. But spinlock can't be nested.