linux-kernel - Re: [PATCH 3/3] fs: befs: Increment i

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Message-ID: <20160604193242.GB14480@ZenIV.linux.org.uk>
Date:	Sat, 4 Jun 2016 20:32:42 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Salah Triki <salah.triki@....org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] fs: befs: Increment i_count when inode is found

On Sat, Jun 04, 2016 at 07:53:21PM +0100, Salah Triki wrote:
> As VFS expects, i_count field is incremented when the named inode is found.

VFS expects no such thing.  Incidentally, you have neither bothered to
check other filesystems nor cared to look at fs/inode.c.  OK, suppose you
have found a huge multi-filesystem bug - such things happen from time to
time.  But you have not even bothered to test your conjecture; this "fix"
had never been tried or even compiled.

What actually happens is that iget_locked() acquires a reference to inode.
That reference is either dropped by iget_failed() (called by befs_iget()
in case of failure to read and initialized the sucker) or used up by
d_add() as a reference to hold dentry->d_inode.

Similar situation holds for other filesystems; they do not need to manipulate
i_count at all.