linux-kernel - Re: [PATCH] xfs: i_state of inode is changed after the inode is freed

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Message-Id: <20060822164847m-saito@mail.aom.tnes.nec.co.jp>
Date:	Tue, 22 Aug 2006 16:48:47 +0900
From:	Masayuki Saito <m-saito@...s.nec.co.jp>
To:	David Chinner <dgc@....com>
Cc:	Nathan Scott <nathans@....com>, xfs@....sgi.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: i_state of inode is changed after the inode is freed

Hi Nathan, David,

I had the vacation too.

David Chinner <dgc@....com> wrote:
>Hmmm - Idon't think we should iput() before we wake up any pinned waiters.
>When we have a waiter on i_ipin_wait (called from xfs_iflush()), we have
>a thread sleeping with the inode locked.
>
>If we then call iput() and it drops the last reference, we can call back
>into the filesystem and start transactions. Those transactions will need
>to lock the inode. Hence I think the above can deadlock when racing against
>an inode flush. 
>
>The code should probably read:
>
>	if (dropped last pincount) {
>		int need_iput = 0;
>		struct inode *inode;
>
>		spin_lock(i_flags_lock)
>		if (!reclaimable) {
>			if (!vp) {
>				if (!(i_state & (NEW|CLEAR))) {
>					inode = igrab(inode)
>					if (inode) {
>						need_iput = 1	
>						mark_inode_dirty_sync(inode)
>					}
>				}
>			}
>		}
>		spin_unlock(i_flags_lock)
>		wake_up(&ip->i_ipin_wait)
>		if (need_iput)
>			iput(inode);
>	}
>
>to avoid this possible deadlock.

OK, I see your point.  There is wait_event(in xfs_iunpin_wait) that should
be wake_up'ed(in xfs_iunpin), so deadlock can occur.

I'll update my patch and test it.  Please wait for a few moments.
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