kernel/linux.git/include/linux/rculist.h, branch linux-7.0.y

rculist: add list_splice_rcu() for private lists

2026-05-23T11:09:26+00:00

[ Upstream commit f902877b635551513729bdf9a8d1422c4aab7741 ] This patch adds a helper function, list_splice_rcu(), to safely splice a private (non-RCU-protected) list into an RCU-protected list. The function ensures that only the pointer visible to RCU readers (prev->next) is updated using rcu_assign_pointer(), while the rest of the list manipulations are performed with regular assignments, as the source list is private and not visible to concurrent RCU readers. This is useful for moving elements from a private list into a global RCU-protected list, ensuring safe publication for RCU readers. Subsystems with some sort of batching mechanism from userspace can benefit from this new function. The function __list_splice_rcu() has been added for clarity and to follow the same pattern as in the existing list_splice*() interfaces, where there is a check to ensure that the list to splice is not empty. Note that __list_splice_rcu() has no documentation for this reason. Reviewed-by: Paul E. McKenney Signed-off-by: Pablo Neira Ayuso Stable-dep-of: a6134e62dba2 ("netfilter: nf_tables: join hook list via splice_list_rcu() in commit phase") Signed-off-by: Sasha Levin

rculist: move list_for_each_rcu() to where it belongs

2025-08-25T17:13:26+00:00

The list_for_each_rcu() relies on the rcu_dereference() API which is not provided by the list.h. At the same time list.h is a low-level basic header that must not have dependencies like RCU, besides the fact of the potential circular dependencies in some cases. With all that said, move RCU related API to the rculist.h where it belongs. Signed-off-by: Andy Shevchenko Reviewed-by: Simona Vetter Reviewed-by: "Paul E. McKenney" Signed-off-by: Neeraj Upadhyay (AMD) Signed-off-by: "Paul E. McKenney"

rculist: add list_bidir_{del,prev}_rcu()

2025-01-09T15:58:52+00:00

Currently there is no primitive for retrieving the previous list member. To do this we need a new deletion primitive that doesn't poison the prev pointer and a corresponding retrieval helper. Note that it is not valid to ues both list_del_rcu() and list_bidir_del_rcu() on the same list. Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-4-6e3cdaf9b280@kernel.org Reviewed-by: Paul E. McKenney Reviewed-by: Jeff Layton Suggested-by: Paul E. McKenney Signed-off-by: Christian Brauner

rcu: Better define "atomic" for list replacement

2024-07-31T15:48:57+00:00

The kernel-doc headers for list_replace_rcu() and hlist_replace_rcu() claim that the replacement is atomic, which it is, but only for readers. Avoid confusion by making it clear that the atomic nature of these functions applies only to readers, not to concurrent updaters. Signed-off-by: Paul E. McKenney Signed-off-by: Neeraj Upadhyay

rculist.h: docs: Fix wrong function summary

2023-12-13T19:44:10+00:00

The brief summary in the docstring for function list_next_or_null_rcu() states that the function is supposed to provide the "first" member of a list, whereas in truth it returns the next member. Change the docstring so it describes what the function actually does. Signed-off-by: Philipp Stanner Signed-off-by: Paul E. McKenney Signed-off-by: Neeraj Upadhyay (AMD)

rculist: Unify documentation about missing list_empty_rcu()

2021-08-06T20:41:48+00:00

We have two separate sections that talk about why list_empty_rcu() is not needed, so this commit consolidates them. Signed-off-by: Julian Wiedmann [ paulmck: The usual wordsmithing. ] Signed-off-by: Paul E. McKenney

rculist: Introduce list/hlist_for_each_entry_srcu() macros

2020-08-25T01:36:09+00:00

list/hlist_for_each_entry_rcu() provides an optional cond argument to specify the lock held in the updater side. However for SRCU read side, not providing the cond argument results into false positive as whether srcu_read_lock is held or not is not checked implicitly. Therefore, on read side the lockdep expression srcu_read_lock_held(srcu struct) can solve this issue. However, the function still fails to check the cases where srcu protected list is traversed with rcu_read_lock() instead of srcu_read_lock(). Therefore, to remove the false negative, this patch introduces two new list traversal primitives : list_for_each_entry_srcu() and hlist_for_each_entry_srcu(). Both of the functions have non-optional cond argument as it is required for both read and update side, and simply checks if the cond is true. For regular read side the lockdep expression srcu_read_lock_head() can be passed as the cond argument to list/hlist_for_each_entry_srcu(). Suggested-by: Paolo Bonzini Tested-by: Suraj Upadhyay Tested-by: Naresh Kamboju [ paulmck: Add "true" per kbuild test robot feedback. ] Signed-off-by: Madhuparna Bhowmik Signed-off-by: Paul E. McKenney

Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-08-03T21:39:35+00:00

Pull locking updates from Ingo Molnar: - LKMM updates: mostly documentation changes, but also some new litmus tests for atomic ops. - KCSAN updates: the most important change is that GCC 11 now has all fixes in place to support KCSAN, so GCC support can be enabled again. Also more annotations. - futex updates: minor cleanups and simplifications - seqlock updates: merge preparatory changes/cleanups for the 'associated locks' facilities. - lockdep updates: - simplify IRQ trace event handling - add various new debug checks - simplify header dependencies, split out , decouple lockdep from other low level headers some more - fix NMI handling - misc cleanups and smaller fixes * tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits) kcsan: Improve IRQ state trace reporting lockdep: Refactor IRQ trace events fields into struct seqlock: lockdep assert non-preemptibility on seqcount_t write lockdep: Add preemption enabled/disabled assertion APIs seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount() seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs seqlock: Reorder seqcount_t and seqlock_t API definitions seqlock: seqcount_t latch: End read sections with read_seqcount_retry() seqlock: Properly format kernel-doc code samples Documentation: locking: Describe seqlock design and usage locking/qspinlock: Do not include atomic.h from qspinlock_types.h locking/atomic: Move ATOMIC_INIT into linux/types.h lockdep: Move list.h inclusion into lockdep.h locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs futex: Remove unused or redundant includes futex: Consistently use fshared as boolean futex: Remove needless goto's futex: Remove put_futex_key() rwsem: fix commas in initialisation docs: locking: Replace HTTP links with HTTPS ones ...

rculist: Add ASSERT_EXCLUSIVE_ACCESS() to __list_splice_init_rcu()

2020-06-29T19:04:48+00:00

After the sync() in __list_splice_init_rcu(), there should be no readers traversing the old list. This commit therefore enlists the help of KCSAN to verify this condition via a pair of calls to ASSERT_EXCLUSIVE_ACCESS(). Signed-off-by: Paul E. McKenney Cc: Marco Elver

rcu: Fix some kernel-doc warnings

2020-06-29T18:58:51+00:00

The current code provokes some kernel-doc warnings: ./kernel/rcu/tree.c:2915: warning: Function parameter or member 'count' not described in 'kfree_rcu_cpu' ./include/linux/rculist.h:517: warning: bad line: [@right ][node2 ... ] ./include/linux/rculist.h:2: WARNING: Unexpected indentation. This commit therefore moves the comment for "count" to the kernel-doc markup and adds a missing "*" on one kernel-doc continuation line. Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Paul E. McKenney