linux-kernel - Re: [PATCH 3/4] vfs: count unlinked inodes

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Message-ID: <CAJfpegsSnu8CeApQ9_9CCwnReADHf_Er6EN0WSTkAFumtm=dQw@mail.gmail.com>
Date:	Mon, 21 Nov 2011 12:51:34 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, jack@...e.cz,
	akpm@...ux-foundation.org, toshi.okajima@...fujitsu.com,
	mszeredi@...e.cz
Subject: Re: [PATCH 3/4] vfs: count unlinked inodes

On Mon, Nov 21, 2011 at 12:34 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Nov 21, 2011 at 12:11:32PM +0100, Miklos Szeredi wrote:
>> Do not WARN_ON if set_nlink is called with zero count, just do a
>> ratelimited printk.  This happens on xfs and probably other
>> filesystems after an unclean shutdown when the filesystem reads inodes
>> which already have zero i_nlink.  Reported by Christoph Hellwig.
>
> Given that this is part of the normal recovery process printing anything
> seems like a bad idea.  I also don't think the code for this actually
> is correct.
>
> Remember when a filesystem recovery from unlinked but open inodes the
> following happens:
>
>  - we walk the list of unlinked but open inodes, and read them into
>   memory, remove the linkage and then iput it.
>
> With the current code that won't ever increment s_remove_count,

It will increment s_remove_count

+void set_nlink(struct inode *inode, unsigned int nlink)
+{
+       if (!nlink) {
+               printk_ratelimited(KERN_INFO
+                       "set_nlink() clearing i_nlink on %s inode %li\n",
+                       inode->i_sb->s_type->name, inode->i_ino);

here:

+               clear_nlink(inode);

> but
> decrement it from __destroy_inode.  I suspect the right fix is to
> simply not warn for a set_nlink to zero, but rather simply increment
> s_remove_count for that case.

I don't really care about the printk.  Without the printk
clear_nlink() is just a shorthand for set_nlink(0), which is fine, but
that's not what the original intention was AFAIK.

Thanks,
Miklos
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