From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 29753361DBA; Mon, 27 Apr 2026 03:46:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777261623; cv=none; b=DjnrwLiswADVIYmN62FhuKC8agR0NqF6BeuaDHHF1L5J4s0GHnaxc0HOzQmG5Nz2182y4d9iOTmJhhwWWVS0T+UDGT31urd6Ufts3L6EQPYty7SoXmajpTXOlb9lGWQvM7UTrT+AxjfzREn/I6L63oJduKMag3XXy2gIIZuojDM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777261623; c=relaxed/simple; bh=PXtHrkpeoeEZCNni7njwoZ/gPRQg81Uvu64iZ5CXssk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rHBNOOrnPgW12zezDFmfdmH79fXvN2yMPA/DRmxCkoepoY0u8w0XykAutti8KLPhrbvfUeFQRtFc7LUFdbhp93OodRO3uiHMU/zQOn3TmcgS6KBYlxJ9ZRiWM+Ir5tqZoBSbtt9K3OruWwnNP0XbHUcw0YWphs+qPqjiZ4N6Ey4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=qaYZ7R1B; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="qaYZ7R1B" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=yX5gniV3PFQjBtZAVsjCI1d+uQEPy+M6yDq46UbG8R4=; b=qaYZ7R1BSz12zM7uf2Pg+BOLEI TaUVYBVdwxpOrDqPxJv+1tXBM6U+0fQ46t7C9VKfseuSBd25/FUIp0dBj4H9guVawLFF16xug3tc8 RXCDk17YKOxrTaGYw0X/yAaxwYUNTeF0VFyo/m0aplUX2MmEDzvwNZ/dJgt10idP3FmL866Xx+IkE D3o9g5gealOy2ZNy+yWUKVmBdQIwXXpVIFeQGOUcW2VgO6G2vN9IND4zEYziIXmsENC4bHcNqyiOZ YsakHfH5mFn/YYhM6B8Djcu7A5+F/8NDSkTSuvnPjQ3qzbjU/xBgUxv3n/j8cNW42jszBirn8XKGi qM+jQ0zw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wHCw1-0000000Avps-1Ify; Mon, 27 Apr 2026 03:47:01 +0000 Date: Mon, 27 Apr 2026 04:47:01 +0100 From: Al Viro To: NeilBrown Cc: Linus Torvalds , Christian Brauner , Jan Kara , Jeff Layton , Trond Myklebust , Anna Schumaker , Miklos Szeredi , Amir Goldstein , Jeremy Kerr , Ard Biesheuvel , Christoph Hellwig , linux-efi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel Subject: Re: [PATCH v2 00/19] Prepare to lift lookup out of exclusive lock for directory ops Message-ID: <20260427034701.GS3518998@ZenIV> References: <20260427033527.773006-1-neilb@ownmail.net> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260427033527.773006-1-neilb@ownmail.net> Sender: Al Viro On Mon, Apr 27, 2026 at 01:29:33PM +1000, NeilBrown wrote: > This patch set progresses my effort to improve concurrency of > directory operations and specifically to allow concurrent updates > in a given directory. > > It is a selection of patches from the 53-patch set I posted in March > which got relatively little response. Maybe a shorter set will be more > approachable. Got it, will post a review tomorrow. > This set: > - prepares the VFS in various ways > - make use of these preparations in ovl and NFS (the most challenging > filesystems for lookup as they do the most interesting things) > - make use in efivars and shmem which for different reasons need a small > change that seemed worth including here. > > The goal that these patch work towards is moving lookup out of i_rwsem > on the directory - except for the actual ->lookup call. This is itself > a step towards allowing broad concurrency of operations in a given > directory. > > There are two particular requirements before lookup can move outside the lock: > 1/ d_drop() mustn't be used before an operation completes: the dentry being present > in the dcache becomes part of the locking protocol. This in turn requires > d_splice_alias() to work with hashed negative dentries. > 2/ d_alloc_parallel() mustn't be called while i_rw_sem is held, as this would > result in a lock inversion. So d_alloc_noblock and others are introduced > to handle the various cases. > In a few cases we need to drop and re-take i_rw_sem inside ->lookup. > As lookup might be called with a shared or exclusive lock this requires > a new LOOKUP_SHARED flag which is ugly but can be removed after the > lookup is moved out of the lock (then ->lookup will only ever be called > with a shared lock). > > The full set of patches including these 19 and the rest to complete the > lifting of lookup out of the exclusive lock can be found at > github/neilbrown/linux in branch pdirops > > Significant changes since last time are: > - use wait_var_event for d_alloc_parallel() rather than effectively > duplicating that infrastructure - as suggested by Christop > - changes to ovl_readdir handling as discussed with Amir. > > Thanks, > NeilBrown > > > [PATCH v2 01/19] VFS: fix various typos in documentation for > [PATCH v2 02/19] VFS: enhance d_splice_alias() to handle in-lookup > [PATCH v2 03/19] VFS: allow d_alloc_name() to be used with ->d_hash > [PATCH v2 04/19] VFS: use wait_var_event for waiting in > [PATCH v2 05/19] VFS: introduce d_alloc_noblock() > [PATCH v2 06/19] VFS: add d_duplicate() > [PATCH v2 07/19] VFS: Add LOOKUP_SHARED flag. > [PATCH v2 08/19] VFS/xfs/ntfs: drop parent lock across > [PATCH v2 09/19] ovl: stop using lookup_one() in iterate_shared() > [PATCH v2 10/19] VFS/ovl: add d_alloc_noblock_return() > [PATCH v2 11/19] efivarfs: use d_alloc_name() > [PATCH v2 12/19] shmem: use d_duplicate() > [PATCH v2 13/19] nfs: remove d_drop()/d_alloc_parallel() from > [PATCH v2 14/19] nfs: use d_splice_alias() in nfs_link() > [PATCH v2 15/19] nfs: don't d_drop() before d_splice_alias() > [PATCH v2 16/19] nfs: don't d_drop() before d_splice_alias() in > [PATCH v2 17/19] nfs: Use d_alloc_noblock() in nfs_prime_dcache() > [PATCH v2 18/19] nfs: use d_alloc_noblock() in silly-rename > [PATCH v2 19/19] nfs: use d_duplicate()