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From: Al Viro <viro@zeniv.linux.org.uk>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	linux-fsdevel@vger.kernel.org,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	NeilBrown <neil@brown.name>, 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: Tue, 5 May 2026 23:50:28 +0100	[thread overview]
Message-ID: <20260505225028.GI3518998@ZenIV> (raw)
In-Reply-To: <afpj3FBrvHer0E6Y@pavilion.home>

On Tue, May 05, 2026 at 11:40:44PM +0200, Frederic Weisbecker wrote:

> > FWIW, back in 2015 spin_lock() did *not* provide an RCU read-side critical
> > area, according to https://lwn.net/Articles/652156/; would be nice to have
> > the history mentioned in D/RCU/whatisRCU.rst - at least to the level of
> > "once upon a time one *did* need an explicit rcu_read_lock() in addition
> > to spin_lock() - spin_lock() or preempt_disable() alone was not enough;
> > that has changed in <...>".
> > 
> > I'm not familiar enough with that code for that kind of archaeology ;-/
> > Could somebody help with that?  Paul?
> 
> That's quite outdated. Now preempt disabled, IRQs disabled, and spinlocks
> are all implicit RCU read sides. On non RT spinlocks disable preemption and
> on RT they call rcu_read_lock() internally.

Out of curiosity, how much headache do bitlocks cause on RT?  I mean, they
are unconditionally disabling preemption, RT or no RT...

  reply	other threads:[~2026-05-05 22:50 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
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 [this message]
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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