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Date: Sat, 2 Jun 2007 15:49:42 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Eric Sandeen <sandeen@sandeen.net>, Jan Kara <jack@suse.cz>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] Fix possible leakage of blocks in UDF
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On Sun, 3 Jun 2007 00:01:46 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:

> [Andrew Morton - Sat, Jun 02, 2007 at 12:16:16PM -0700]
> [...snip...]
> | 
> | No, the problem is that the patch caused the kernel to take inode_lock
> | within the newly-added drop_inode(), btu drop_inode() is already called
> | under inode_lock.
> | 
> | It has nothing to do with lock_kernel() and it has nothing to do with
> | sleeping.
> | 
> 
> Andrew, the only call that could leading to subseq. inode_lock lock
> is mark_inode_dirty() I guess (and that is snown by Eric's dump)
> but as I shown you in my dbg print without SMP it's OK. So
> is it SMP who lead to lock? How it depends on it? (I understand
> that is a stupid question for you but if you have time explain
> me this please ;)
> 

When CONFIG_SMP=n, spin_lock() is a no-op.  (Except with CONFIG_PREEMPT=y,
in which case spin_lock() will disable kernel preemption on SMP and non-SMP
kernels)

When CONFIG_SMP=y, spin_lock() really does take a lock.  But if this thread
already holds this lock, we'll deadlock.