linux-kernel - Re: [RFC] freeing unlinked file indefinitely delayed

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Message-ID: <20150712150035.GJ17109@ZenIV.linux.org.uk>
Date:	Sun, 12 Jul 2015 16:00:35 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ben Myers <bpm@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC] freeing unlinked file indefinitely delayed

On Wed, Jul 08, 2015 at 10:41:43AM -0500, Ben Myers wrote:

> The bug rings a bell for me so I will stick my neck out instead of
> lurking.  Don't you need to sample that link count under the filesystems
> internal lock in order to avoid an unlink/iget race?  I suggest creating
> a helper to prune disconnected dentries which a filesystem could call in
> .unlink.  That would avoid the risk of unintended side effects with the
> d_alloc/d_free/icache approach and have provable link count correctness.

For one thing, this patch does *not* check for i_nlink at all.  For another,
there's no such thing as 'filesystems internal lock' for i_nlink protection -
that's handled by i_mutex...  And what does iget() have to do with any of that?
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