linux-kernel - Re: [PATCH] Fix i_mutex handling in nfsd readdir.

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Date:	Sat, 18 Apr 2009 12:11:54 +0900
From:	hooanon05@...oo.co.jp
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>, bfields@...i.umich.edu,
	hch@...radead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Fix i_mutex handling in nfsd readdir. 


David Woodhouse:
> This patch fixes it by locking the directory's i_mutex again before
> calling the filldir functions. The original deadlocks which commit
> 14f7dd63 was designed to avoid are still avoided, because they were due
> to fs-internal locking, not i_mutex.
	:::
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1248,6 +1248,8 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
>  	int err;
>  	struct qstr this;
>  
> +	WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
> +
>  	err = __lookup_one_len(name, &this, base, len);

I'd suggest this checking is done only when CONFIG_DEBUG_KERNEL (or
something) is enabled. Because unconditional checking costs high for the
well-reviewed lookup code.


J. R. Okajima
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