From: Amir Goldstein <amir73il@gmail.com>
To: NeilBrown <neil@brown.name>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
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>, 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 07/19] VFS: Add LOOKUP_SHARED flag.
Date: Mon, 27 Apr 2026 09:43:04 +0200 [thread overview]
Message-ID: <CAOQ4uxi8rqkbhK4=8N1ncfU1m6bjdHLbinSf=j3k0oVEaSa-wA@mail.gmail.com> (raw)
In-Reply-To: <20260427040517.828226-8-neilb@ownmail.net>
On Mon, Apr 27, 2026 at 6:06 AM NeilBrown <neilb@ownmail.net> wrote:
>
> From: NeilBrown <neil@brown.name>
>
> Some ->lookup handlers will need to drop and retake the parent lock, so
> they can safely use d_alloc_parallel().
>
> ->lookup can be called with the parent lock either exclusive or shared.
>
> A new flag, LOOKUP_SHARED, tells ->lookup how the parent is locked.
>
> This is rather ugly, but will be gone soon after we move
> d_alloc_parallel() out of the directory lock as ->lookup() will *always*
> called with a shared lock on the parent.
Neil,
Forgive me for being skeptical about the *always* part.
How long ago did we add ->iterate_shared()?
It's true that Linus eventually got rid of ->iterate(), but we did not
get rid of the assumption that iterate_shared() might be upgraded
to exclusive lock.
The obvious reason is that *someone* needs to do this work for
old filesystems, which are also hard to test and nobody wants to
touch them.
I have nothing against this patch, but I think it is more realistic
to state that LOOKUP_SHARED is here to stay, so if you think it
is too ugly, maybe there is something to be done about it.
Personally, I do not see the ugliness though.
Am I misjudging the situation of shared lookup wrt old filesystems?
Thanks,
Amir.
next prev parent reply other threads:[~2026-04-27 7:43 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 4:01 [PATCH v3 00/19] Prepare to lift lookup out of exclusive lock for directory ops NeilBrown
2026-04-27 4:01 ` [PATCH v3 01/19] VFS: fix various typos in documentation for start_creating start_removing etc NeilBrown
2026-04-27 4:01 ` [PATCH v3 02/19] VFS: enhance d_splice_alias() to handle in-lookup dentries NeilBrown
2026-04-27 4:01 ` [PATCH v3 03/19] VFS: allow d_alloc_name() to be used with ->d_hash NeilBrown
2026-04-28 2:10 ` Al Viro
2026-04-29 2:44 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 04/19] VFS: use wait_var_event for waiting in d_alloc_parallel() NeilBrown
2026-04-28 3:37 ` Al Viro
2026-04-28 11:18 ` NeilBrown
2026-04-28 14:22 ` Al Viro
2026-04-28 23:26 ` NeilBrown
2026-04-29 5:26 ` Al Viro
2026-04-29 17:07 ` Al Viro
2026-04-29 21:03 ` Linus Torvalds
2026-04-30 23:51 ` NeilBrown
2026-05-01 1:11 ` Al Viro
2026-05-01 1:39 ` NeilBrown
2026-05-01 1:45 ` NeilBrown
2026-05-01 3:37 ` Al Viro
2026-05-01 10:46 ` NeilBrown
2026-05-01 1:20 ` NeilBrown
2026-04-28 16:32 ` Linus Torvalds
2026-04-27 4:01 ` [PATCH v3 05/19] VFS: introduce d_alloc_noblock() NeilBrown
2026-04-28 2:22 ` Al Viro
2026-04-28 11:24 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 06/19] VFS: add d_duplicate() NeilBrown
2026-04-27 4:01 ` [PATCH v3 07/19] VFS: Add LOOKUP_SHARED flag NeilBrown
2026-04-27 7:43 ` Amir Goldstein [this message]
2026-04-27 8:47 ` NeilBrown
2026-04-27 9:05 ` Amir Goldstein
2026-04-27 23:51 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 08/19] VFS/xfs/ntfs: drop parent lock across d_alloc_parallel() in d_add_ci() NeilBrown
2026-04-27 7:49 ` Amir Goldstein
2026-04-27 8:48 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 09/19] ovl: stop using lookup_one() in iterate_shared() handling NeilBrown
2026-04-27 10:10 ` Amir Goldstein
2026-04-28 0:24 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 10/19] VFS/ovl: add d_alloc_noblock_return() NeilBrown
2026-04-27 9:40 ` Amir Goldstein
2026-04-28 0:34 ` NeilBrown
2026-04-28 4:35 ` Al Viro
2026-04-28 11:44 ` NeilBrown
2026-04-27 4:01 ` [PATCH v3 11/19] efivarfs: use d_alloc_name() NeilBrown
2026-04-27 4:01 ` [PATCH v3 12/19] shmem: use d_duplicate() NeilBrown
2026-04-27 4:01 ` [PATCH v3 13/19] nfs: remove d_drop()/d_alloc_parallel() from nfs_atomic_open() NeilBrown
2026-04-27 4:01 ` [PATCH v3 14/19] nfs: use d_splice_alias() in nfs_link() NeilBrown
2026-04-27 4:01 ` [PATCH v3 15/19] nfs: don't d_drop() before d_splice_alias() NeilBrown
2026-04-27 4:01 ` [PATCH v3 16/19] nfs: don't d_drop() before d_splice_alias() in atomic_create NeilBrown
2026-04-27 4:01 ` [PATCH v3 17/19] nfs: Use d_alloc_noblock() in nfs_prime_dcache() NeilBrown
2026-04-27 4:01 ` [PATCH v3 18/19] nfs: use d_alloc_noblock() in silly-rename NeilBrown
2026-04-27 4:01 ` [PATCH v3 19/19] nfs: use d_duplicate() NeilBrown
2026-04-27 8:42 ` [syzbot ci] Re: Prepare to lift lookup out of exclusive lock for directory ops syzbot ci
2026-04-28 23:16 ` NeilBrown
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