From: Al Viro <viro@zeniv.linux.org.uk>
To: NeilBrown <neil@brown.name>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>
Subject: Re: [RFC PATCH 02/25] alloc_path_pseudo(): make sure we don't end up with NORCU dentries for directories
Date: Tue, 5 May 2026 18:48:44 +0100 [thread overview]
Message-ID: <20260505174844.GE3518998@ZenIV> (raw)
In-Reply-To: <177796931573.1474915.17389032143652405017@noble.neil.brown.name>
On Tue, May 05, 2026 at 06:21:55PM +1000, NeilBrown wrote:
> On Tue, 05 May 2026, Al Viro wrote:
> > A lot of places relies upon directories never having NORCU dentries;
> > currently that property holds, but the proof is not straightforward
> > and rather brittle.
>
> This requirement is only indirectly documented in d_alloc_pseudo()
> where it says "the stuff that should never be anyone's children or
> parents", and they are for "lookup-less filesystems" wherein directories
> obviously cannot have a role.
> Would it be worth making it explicit?
> "A pseudo dentry must never be used for a directory"
The comment in d_alloc_pseudo() is going to be replaced; currently it's
flat-out inaccurate - memfd_create(2) will result in a NORCU dentry
on tmpfs, which is very definitely *NOT* a lookup-less filesystem.
I have a half-finished documentation on the rules for NORCU dentries -
adding that is in the "yet to be stabilized" local followups to this
series. I hope to get that dealt with during this cycle - this is not
the final iteration of that patchset.
next prev parent reply other threads:[~2026-05-05 17:48 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-05 5:53 [RFC PATCH 00/25] assorted dcache cleanups and fixes Al Viro
2026-05-05 5:53 ` [RFC PATCH 01/25] VFS: use wait_var_event for waiting in d_alloc_parallel() Al Viro
2026-05-05 5:53 ` [RFC PATCH 02/25] alloc_path_pseudo(): make sure we don't end up with NORCU dentries for directories Al Viro
2026-05-05 8:21 ` NeilBrown
2026-05-05 17:48 ` Al Viro [this message]
2026-05-05 5:53 ` [RFC PATCH 03/25] fix a race between d_find_any_alias() and final dput() of NORCU dentries Al Viro
2026-05-05 17:06 ` Linus Torvalds
2026-05-05 20:29 ` Al Viro
2026-05-05 5:53 ` [RFC PATCH 04/25] find_acceptable_alias(): skip NORCU aliases with zero refcount Al Viro
2026-05-05 5:53 ` [RFC PATCH 05/25] select_collect(): ignore dentries on shrink lists if they have positive refcounts Al Viro
2026-05-05 5:53 ` [RFC PATCH 06/25] make to_shrink_list() return whether it has moved dentry to list Al Viro
2026-05-05 5:53 ` [RFC PATCH 07/25] kill d_dispose_if_unused() Al Viro
2026-05-05 5:53 ` [RFC PATCH 08/25] d_prune_aliases(): make sure to skip NORCU aliases Al Viro
2026-05-05 5:53 ` [RFC PATCH 09/25] shrink_dentry_list(): start with removing from shrink list Al Viro
2026-05-07 20:39 ` Al Viro
2026-05-05 5:53 ` [RFC PATCH 10/25] fold lock_for_kill() into shrink_kill() Al Viro
2026-05-05 5:53 ` [RFC PATCH 11/25] fold lock_for_kill() and __dentry_kill() into common helper Al Viro
2026-05-05 5:53 ` [RFC PATCH 12/25] reducing rcu_read_lock() scopes in dput and friends, step 1 Al Viro
2026-05-05 8:55 ` NeilBrown
2026-05-05 14:22 ` Al Viro
2026-05-05 21:58 ` NeilBrown
2026-05-05 16:47 ` Linus Torvalds
2026-05-05 22:42 ` Al Viro
2026-05-07 7:35 ` Al Viro
2026-05-07 15:32 ` Linus Torvalds
2026-05-05 5:54 ` [RFC PATCH 13/25] reducing rcu_read_lock() scopes in dput and friends, step 2 Al Viro
2026-05-05 5:54 ` [RFC PATCH 14/25] reducing rcu_read_lock() scopes in dput and friends, step 3 Al Viro
2026-05-05 5:54 ` [RFC PATCH 15/25] reducing rcu_read_lock() scopes in dput and friends, step 4 Al Viro
2026-05-05 5:54 ` [RFC PATCH 16/25] reducing rcu_read_lock() scopes in dput and friends, step 5 Al Viro
2026-05-05 5:54 ` [RFC PATCH 17/25] reducing rcu_read_lock() scopes in dput and friends, step 6 Al Viro
2026-05-05 5:54 ` [RFC PATCH 18/25] adjust calling conventions of lock_for_kill(), fold __dentry_kill() into dentry_kill() Al Viro
2026-05-05 5:54 ` [RFC PATCH 19/25] document dentry_kill() Al Viro
2026-05-05 5:54 ` [RFC PATCH 20/25] d_walk(): shrink rcu_read_lock() scope Al Viro
2026-05-05 17:01 ` Linus Torvalds
2026-05-05 20:05 ` Al Viro
2026-05-05 21:40 ` Frederic Weisbecker
2026-05-05 22:50 ` Al Viro
2026-05-06 3:49 ` Paul E. McKenney
2026-05-07 22:39 ` NeilBrown
2026-05-07 23:21 ` Paul E. McKenney
2026-05-08 14:47 ` Al Viro
2026-05-08 22:03 ` Paul E. McKenney
2026-05-08 23:03 ` Al Viro
2026-05-08 3:01 ` Al Viro
2026-05-05 5:54 ` [RFC PATCH 21/25] shrinking rcu_read_lock() scope in d_alloc_parallel() Al Viro
2026-05-07 21:52 ` Jori Koolstra
2026-05-08 3:12 ` Al Viro
2026-05-08 9:28 ` Jori Koolstra
2026-05-05 5:54 ` [RFC PATCH 22/25] shrink_dentry_tree(): unify the calls of shrink_dentry_list() Al Viro
2026-05-05 5:54 ` [RFC PATCH 23/25] wind ->s_roots via ->d_sib instead of ->d_hash Al Viro
2026-05-05 5:54 ` [RFC PATCH 24/25] nfs: get rid of fake root dentries Al Viro
2026-05-05 5:54 ` [RFC PATCH 25/25] make cursors NORCU Al Viro
2026-05-05 17:09 ` [RFC PATCH 00/25] assorted dcache cleanups and fixes Linus Torvalds
2026-06-05 5:08 ` [PATCH v2 00/22] " Al Viro
2026-06-05 5:08 ` [PATCH v2 01/22] VFS: use wait_var_event for waiting in d_alloc_parallel() Al Viro
2026-06-05 5:08 ` [PATCH v2 02/22] alloc_path_pseudo(): make sure we don't end up with NORCU dentries for directories Al Viro
2026-06-05 5:08 ` [PATCH v2 03/22] fix a race between d_find_any_alias() and final dput() of NORCU dentries Al Viro
2026-06-05 5:08 ` [PATCH v2 04/22] find_acceptable_alias(): skip NORCU aliases with zero refcount Al Viro
2026-06-05 5:08 ` [PATCH v2 05/22] select_collect(): ignore dentries on shrink lists if they have positive refcounts Al Viro
2026-06-05 5:08 ` [PATCH v2 06/22] make to_shrink_list() return whether it has moved dentry to list Al Viro
2026-06-05 5:08 ` [PATCH v2 07/22] kill d_dispose_if_unused() Al Viro
2026-06-05 5:08 ` [PATCH v2 08/22] d_prune_aliases(): make sure to skip NORCU aliases Al Viro
2026-06-05 5:08 ` [PATCH v2 09/22] shrink_dentry_list(): start with removing from shrink list Al Viro
2026-06-05 5:08 ` [PATCH v2 10/22] fold lock_for_kill() into shrink_kill() Al Viro
2026-06-05 5:08 ` [PATCH v2 11/22] fold lock_for_kill() and __dentry_kill() into common helper Al Viro
2026-06-05 5:09 ` [PATCH v2 12/22] simplify safety for lock_for_kill() slowpath Al Viro
2026-06-05 5:09 ` [PATCH v2 13/22] Shift rcu_read_{,un}lock() inside fast_dput() Al Viro
2026-06-05 5:09 ` [PATCH v2 14/22] Document rcu_read_lock() use in select_collect2() Al Viro
2026-06-05 5:09 ` [PATCH v2 15/22] adjust calling conventions of lock_for_kill(), fold __dentry_kill() into dentry_kill() Al Viro
2026-06-05 5:09 ` [PATCH v2 16/22] document dentry_kill() Al Viro
2026-06-05 5:09 ` [PATCH v2 17/22] d_walk(): shrink rcu_read_lock() scope Al Viro
2026-06-05 5:09 ` [PATCH v2 18/22] shrinking rcu_read_lock() scope in d_alloc_parallel() Al Viro
2026-06-05 5:09 ` [PATCH v2 19/22] shrink_dentry_tree(): unify the calls of shrink_dentry_list() Al Viro
2026-06-05 5:09 ` [PATCH v2 20/22] wind ->s_roots via ->d_sib instead of ->d_hash Al Viro
2026-06-05 5:09 ` [PATCH v2 21/22] nfs: get rid of fake root dentries Al Viro
2026-06-05 5:09 ` [PATCH v2 22/22] make cursors NORCU Al Viro
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