[PATCH v2 00/14] list: Prepare entry iterators to cache cursor state

[Christian König]

On 6/9/26 08:13, Kaitao Cheng wrote:
> From: Kaito Cheng <chengkaitao at kylinos.cn>
> 
> This series prepares for, and then updates, the list_for_each_entry()
> family so the common entry iterators cache their next or previous cursor
> before the loop body runs.

Why in the world would we want to do that?

The safe and non-safe variants have very distinct use cases and that is completely intentional.

What we could improve maybe is the documentation, from my experience an astonishing large amount of people have misconceptions about the safe variants.

> The first 13 patches open-code loops that intentionally depend on the
> old "derive the next entry from the current cursor at the end of the
> iteration" behaviour.  These loops append work to the list being walked,
> restart traversal after dropping a lock, skip an entry consumed by the
> current iteration, or otherwise adjust the cursor in the loop body.

Well I have to clearly reject the changes for subsystems/components I'm maintaining, that just looks horrible to me and I clearly don't see a good reason for that.

Regards,
Christian.

> 
> The final patch changes include/linux/list.h to keep a private cursor in
> the common entry iterators while preserving the public macro interface.
> The safe variants remain available when callers need the temporary
> cursor explicitly or have stronger mutation requirements.
> 
> 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 v1:
> https://lore.kernel.org/all/20260529082149.76764-1-kaitao.cheng@linux.dev/
> 
> Kaitao Cheng (14):
>   drbd: Open-code transfer log list walk
>   firewire: core: Open-code topology list walk
>   drm/bridge: Open-code bridge chain list walks
>   drm/i915/gt: Open-code active timeline walk
>   drm/i915: Open-code DFS dependency list walk
>   drm/ttm: Open-code reservation list walk
>   spi: fsi: Open-code message transfer walk
>   spi: stm32-ospi: Open-code message transfer walk
>   spi: stm32-qspi: Open-code message transfer walk
>   spi: tegra210-quad: Open-code message transfer walk
>   locking/locktorture: Open-code ww mutex list walk
>   locking/ww_mutex: Open-code stress reorder list walk
>   ASoC: dapm: Open-code widget invalidation walk
>   list: Cache cursors in entry iterators
> 
>  drivers/block/drbd/drbd_debugfs.c      |  4 ++-
>  drivers/firewire/core-topology.c       |  4 ++-
>  drivers/gpu/drm/drm_bridge.c           |  7 ++--
>  drivers/gpu/drm/i915/gt/intel_reset.c  |  4 ++-
>  drivers/gpu/drm/i915/i915_scheduler.c  |  4 ++-
>  drivers/gpu/drm/ttm/ttm_execbuf_util.c |  4 ++-
>  drivers/spi/spi-fsi.c                  |  5 ++-
>  drivers/spi/spi-stm32-ospi.c           |  4 ++-
>  drivers/spi/spi-stm32-qspi.c           |  5 ++-
>  drivers/spi/spi-tegra210-quad.c        |  4 ++-
>  include/linux/list.h                   | 46 ++++++++++++++++++++------
>  kernel/locking/locktorture.c           |  4 ++-
>  kernel/locking/test-ww_mutex.c         |  4 ++-
>  sound/soc/soc-dapm.c                   |  4 ++-
>  14 files changed, 78 insertions(+), 25 deletions(-)
> 
> --
> 2.43.0
>