Re: [PATCH v3 0/7] Prepare mutable list iterators to cache cursor state

[Alexei Starovoitov]

On Sun, Jun 21, 2026 at 9:06 PM Kaitao Cheng <kaitao.cheng@xxxxxxxxx> wrote:
>
> From: chengkaitao <chengkaitao@xxxxxxxxxx>
>
> The list_for_each*_safe() helpers are used when the loop body may remove
> the current entry.  Their current interface, however, forces every caller
> to define a temporary cursor outside the macro and pass it in, even when
> the caller never uses that cursor directly.  For most call sites this
> extra cursor is just boilerplate required by the macro implementation.
>
> This is awkward because the saved next pointer is an internal detail of
> the iteration.  Callers that only remove or move the current entry do not
> need to spell it out.
>
> The _safe() suffix has also caused confusion.  Christian Koenig pointed
> out that the name is easy to read as a thread-safe variant, especially
> for beginners, even though it only means that the iterator keeps enough
> state to tolerate removal of the current entry.  He suggested _mutable()
> as a clearer description of what the loop permits.
>
> Add *_mutable() iterator variants for list, hlist and llist.  The new
> helpers are variadic and support both forms.  In the common case, the
> caller omits the temporary cursor and the macro creates a unique internal
> cursor with typeof(pos) and __UNIQUE_ID().  If a loop really needs an
> explicit temporary cursor, the caller can still pass it and the helper
> keeps the existing *_safe() behaviour.
>
> For example, a call site may use the shorter form:
>
>   list_for_each_entry_mutable(pos, head, member)
>
> or keep the explicit temporary cursor form:
>
>   list_for_each_entry_mutable(pos, tmp, head, member)
>
> The existing *_safe() helpers remain available for compatibility.  This
> series only converts users in mm, block, kernel, init and io_uring.  If
> this approach looks acceptable, the remaining users can be converted in
> follow-up series.
>
> Changes in v3 (Christian König, Andy Shevchenko):
> - Convert safe list walks to mutable iterators
>
> Changes in v2 (Muchun Song, Andy Shevchenko):
> - Drop the list_for_each_entry_mutable*() helpers from v1 and make the
>   cursor change directly in the existing list_for_each_entry*() helpers.
> - Open-code special list walks that rely on updating the loop cursor in
>   the body, preserving their existing traversal semantics.
>
> Link to v2:
> https://lore.kernel.org/all/20260609061347.93688-1-kaitao.cheng@xxxxxxxxx/
>
> Link to v1:
> https://lore.kernel.org/all/20260529082149.76764-1-kaitao.cheng@xxxxxxxxx/
>
> Kaitao Cheng (7):
>   list: Add mutable iterator variants
>   llist: Add mutable iterator variants
>   mm: Use mutable list iterators
>   block: Use mutable list iterators
>   kernel: Use mutable list iterators
>   initramfs: Use mutable list iterator
>   io_uring: Use mutable list iterators
>
>  block/bfq-iosched.c                 |  17 +-
>  block/blk-cgroup.c                  |  12 +-
>  block/blk-flush.c                   |   4 +-
>  block/blk-iocost.c                  |  18 +-
>  block/blk-mq.c                      |   8 +-
>  block/blk-throttle.c                |   4 +-
>  block/kyber-iosched.c               |   4 +-
>  block/partitions/ldm.c              |   8 +-
>  block/sed-opal.c                    |   4 +-
>  include/linux/list.h                | 269 ++++++++++++++++++++++++----
>  include/linux/llist.h               |  81 +++++++--
>  init/initramfs.c                    |   5 +-
>  io_uring/cancel.c                   |   6 +-
>  io_uring/poll.c                     |   3 +-
>  io_uring/rw.c                       |   4 +-
>  io_uring/timeout.c                  |   8 +-
>  io_uring/uring_cmd.c                |   3 +-
>  kernel/audit_tree.c                 |   4 +-
>  kernel/audit_watch.c                |  16 +-
>  kernel/auditfilter.c                |   4 +-
>  kernel/auditsc.c                    |   4 +-
>  kernel/bpf/arena.c                  |  10 +-
>  kernel/bpf/arraymap.c               |   8 +-
>  kernel/bpf/bpf_local_storage.c      |   3 +-
>  kernel/bpf/bpf_lru_list.c           |  25 ++-
>  kernel/bpf/btf.c                    |  18 +-
>  kernel/bpf/cgroup.c                 |   7 +-
>  kernel/bpf/cpumap.c                 |   4 +-
>  kernel/bpf/devmap.c                 |  10 +-
>  kernel/bpf/helpers.c                |   8 +-
>  kernel/bpf/local_storage.c          |   4 +-
>  kernel/bpf/memalloc.c               |  16 +-
>  kernel/bpf/offload.c                |   8 +-
>  kernel/bpf/states.c                 |   4 +-
>  kernel/bpf/stream.c                 |   4 +-
>  kernel/bpf/verifier.c               |   6 +-
>  kernel/cgroup/cgroup-v1.c           |   4 +-
>  kernel/cgroup/cgroup.c              |  54 +++---
>  kernel/cgroup/dmem.c                |  12 +-
>  kernel/cgroup/rdma.c                |   8 +-
>  kernel/events/core.c                |  44 +++--
>  kernel/events/uprobes.c             |  12 +-
>  kernel/exit.c                       |   8 +-
>  kernel/fail_function.c              |   4 +-
>  kernel/gcov/clang.c                 |   4 +-
>  kernel/irq_work.c                   |   4 +-
>  kernel/kexec_core.c                 |   4 +-
>  kernel/kprobes.c                    |  16 +-
>  kernel/livepatch/core.c             |   4 +-
>  kernel/livepatch/core.h             |   4 +-
>  kernel/liveupdate/kho_block.c       |   4 +-
>  kernel/liveupdate/luo_flb.c         |   4 +-
>  kernel/locking/rwsem.c              |   2 +-
>  kernel/locking/test-ww_mutex.c      |   2 +-
>  kernel/module/main.c                |  11 +-
>  kernel/padata.c                     |   4 +-
>  kernel/power/snapshot.c             |   8 +-
>  kernel/power/wakelock.c             |   4 +-
>  kernel/printk/printk.c              |  11 +-
>  kernel/ptrace.c                     |   4 +-
>  kernel/rcu/rcutorture.c             |   3 +-
>  kernel/rcu/tasks.h                  |   9 +-
>  kernel/rcu/tree.c                   |   6 +-
>  kernel/resource.c                   |   4 +-
>  kernel/sched/core.c                 |   4 +-
>  kernel/sched/ext.c                  |  22 +--
>  kernel/sched/fair.c                 |  28 +--
>  kernel/sched/topology.c             |   4 +-
>  kernel/sched/wait.c                 |   4 +-
>  kernel/seccomp.c                    |   4 +-
>  kernel/signal.c                     |  11 +-
>  kernel/smp.c                        |   4 +-
>  kernel/taskstats.c                  |   8 +-
>  kernel/time/clockevents.c           |   6 +-
>  kernel/time/clocksource.c           |   4 +-
>  kernel/time/posix-cpu-timers.c      |   4 +-
>  kernel/time/posix-timers.c          |   3 +-
>  kernel/torture.c                    |   3 +-
>  kernel/trace/bpf_trace.c            |   4 +-
>  kernel/trace/ftrace.c               |  49 +++--
>  kernel/trace/ring_buffer.c          |  25 ++-
>  kernel/trace/trace.c                |  12 +-
>  kernel/trace/trace_dynevent.c       |   6 +-
>  kernel/trace/trace_dynevent.h       |   5 +-
>  kernel/trace/trace_events.c         |  35 ++--
>  kernel/trace/trace_events_filter.c  |   4 +-
>  kernel/trace/trace_events_hist.c    |   8 +-
>  kernel/trace/trace_events_trigger.c |  17 +-
>  kernel/trace/trace_events_user.c    |  16 +-
>  kernel/trace/trace_stat.c           |   4 +-
>  kernel/user-return-notifier.c       |   3 +-
>  kernel/workqueue.c                  |  16 +-
>  mm/backing-dev.c                    |   8 +-
>  mm/balloon.c                        |   8 +-
>  mm/cma.c                            |   4 +-
>  mm/compaction.c                     |   4 +-
>  mm/damon/core.c                     |   4 +-
>  mm/damon/sysfs-schemes.c            |   4 +-
>  mm/dmapool.c                        |   4 +-
>  mm/huge_memory.c                    |   8 +-
>  mm/hugetlb.c                        |  56 +++---
>  mm/hugetlb_vmemmap.c                |  16 +-
>  mm/khugepaged.c                     |  14 +-
>  mm/kmemleak.c                       |   7 +-
>  mm/ksm.c                            |  25 +--
>  mm/list_lru.c                       |   4 +-
>  mm/memcontrol-v1.c                  |   8 +-
>  mm/memory-failure.c                 |  12 +-
>  mm/memory-tiers.c                   |   4 +-
>  mm/migrate.c                        |  23 ++-
>  mm/mmu_notifier.c                   |   9 +-
>  mm/page_alloc.c                     |   8 +-
>  mm/page_reporting.c                 |   2 +-
>  mm/percpu.c                         |  11 +-
>  mm/pgtable-generic.c                |   4 +-
>  mm/rmap.c                           |  10 +-
>  mm/shmem.c                          |   9 +-
>  mm/slab_common.c                    |  14 +-
>  mm/slub.c                           |  33 ++--
>  mm/swapfile.c                       |   4 +-
>  mm/userfaultfd.c                    |  12 +-
>  mm/vmalloc.c                        |  24 +--
>  mm/vmscan.c                         |   7 +-
>  mm/zsmalloc.c                       |   4 +-
>  124 files changed, 875 insertions(+), 681 deletions(-)

Not sure what you were thinking, but this diff stat
is not landable.

pw-bot: cr