linux-kernel - Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU symlinks

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Message-ID: <20150516015540.GP7232@ZenIV.linux.org.uk>
Date:	Sat, 16 May 2015 02:55:40 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	NeilBrown <neilb@...e.de>, Andreas Dilger <adilger@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC][PATCHSET v3] non-recursive pathname resolution & RCU
 symlinks

On Fri, May 15, 2015 at 06:47:04PM -0700, Linus Torvalds wrote:

> Now, maybe we could solve it with a new sleeping lock in the dentry
> itself. Maybe we could allocate the new dentry early, add it to the
> directory the usual way, but mark it as being "not ready" (so that
> d_lookup() wouldn't use it). And have the sleeping lock be a new
> sleeping lock in the dentry.

See upthread.  It might be doable (provided that we turn ->i_mutex into
rwsem, to keep the exclusion with directory _modifiers_), but it'll need
a really non-trivial code review of a bunch of filesystems, especially ones
that want to play with the list of children like ceph does.  And things
like sillyrename and dcache-populating readdir instances, albeit not as scary
as ceph.  And then there's lustre...
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