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	Tue, 28 Apr 2026 02:22:45 +0000
Date: Tue, 28 Apr 2026 03:22:45 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: NeilBrown <neil@brown.name>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Jeff Layton <jlayton@kernel.org>,
	Trond Myklebust <trondmy@kernel.org>,
	Anna Schumaker <anna@kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Amir Goldstein <amir73il@gmail.com>, Jeremy Kerr <jk@ozlabs.org>,
	Ard Biesheuvel <ardb@kernel.org>, linux-efi@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
	linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 05/19] VFS: introduce d_alloc_noblock()
Message-ID: <20260428022245.GU3518998@ZenIV>
References: <20260427040517.828226-1-neilb@ownmail.net>
 <20260427040517.828226-6-neilb@ownmail.net>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Mon, Apr 27, 2026 at 02:01:23PM +1000, NeilBrown wrote:
> From: NeilBrown <neil@brown.name>
> 
> Several filesystems use the results of readdir to prime the dcache.
> These filesystems use d_alloc_parallel() which can block if there is a
> concurrent lookup.  Blocking in that case is pointless as the lookup
> will add info to the dcache and there is no value in the readdir waiting
> to see if it should add the info too.

... except that there is - large part of the reasons for that in the original
user (procfs) is that we want getdents() + open() + fstat() + compare ->st_ino
from fstat() with ->d_ino from getdents() to work, even if you race with lookup
from another process coming in the middle of your getdents().

What are your plans in that area?