From: Al Viro <viro@zeniv.linux.org.uk>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: NeilBrown <neil@brown.name>,
Frederic Weisbecker <frederic@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Boqun Feng <boqun@kernel.org>,
Joel Fernandes <joelagnelf@nvidia.com>,
Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [RFC PATCH 20/25] d_walk(): shrink rcu_read_lock() scope
Date: Fri, 8 May 2026 15:47:54 +0100 [thread overview]
Message-ID: <20260508144754.GB2636677@ZenIV> (raw)
In-Reply-To: <586a6402-ae1a-47c5-b054-f02cbd457928@paulmck-laptop>
On Thu, May 07, 2026 at 04:21:28PM -0700, Paul E. McKenney wrote:
> Alternatively, if the bitlock acquisition is always a trylock-style
> operation with no tight loop around the trylock, it should not be
> necessary to disable preemption. (Give or take the expectations of the
> code in the critical section, of course!)
In dcache we have two of those - hash chains in the main dentry hash
(insertion and removal only; RCU for traversals) and, more unpleasantly,
hash chains in the in-lookup hash. Those have search-and-insert-new
and removal, the former with full traversal of the chain under the
lock.
The entries are there for duration of ->lookup(), so it stuffing a lot
of them in there might be feasible with a bunch of lookups for different
names on a stuck network filesystem (each with a separate thread blocked
waiting for server to reply)...
next prev parent reply other threads:[~2026-05-08 14:47 UTC|newest]
Thread overview: 53+ 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
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 [this message]
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
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