linux-kernel - Re: [RFC PATCH] shrink_dcache

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Date:	Mon, 9 Jan 2012 21:26:55 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Chinner <david@...morbit.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	mgorman@...e.de, gregkh@...e.de, akpm@...ux-foundation.org
Subject: Re: [RFC PATCH] shrink_dcache_parent() deadlock

On Tue, Jan 10, 2012 at 07:59:07AM +1100, Dave Chinner wrote:
> > Comments?
> 
> Looks OK to me.

OK, grabbed.  And there's *more* fixes for obvious shite - by now I'm
really sick and tired of what people are doing with failure exits;
this morning catch just from looking through d_alloc_root() callers:
	isofs - inode leak
	ext4 - dentry leak + completely bogus handling of ext4_mb_init()
failure (stuff that hadn't been allocated gets freed, stuff that was
allocated isn't)
	ceph - d_alloc_root() can fail.  NULL pointer derefs galore...
)

Frankly, d_alloc_root() had been a bad API; it should've been doing
iput() on allocation failure.  I've added a trivial helper in the
local tree (d_make_root(inode) - same as d_alloc_root(inode) and do
iput(inode) if result turns out to be NULL).  Looks like *all* callers
of d_alloc_root() either turn out to be buggy or trivially convert to
d_make_root().  With a lot of boilerplate crap removed...

Hell knows...  Originally I thought about leaving both side-by-side, but
it really starts looking as if there's no reason to keep d_alloc_root()
at all...  I still have a couple of callers to check, though.
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