Re: [PATCH v2 0/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:26PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@xxxxxxxxxx>
>
> Introduce for_each_process_rculock(), for_each_thread_rculock() and
> for_each_process_thread_rculock() macros that combine the existing
> iteration macros with scoped_guard(rcu), so that the RCU read lock
> is automatically acquired before iteration and released when the
> loop exits — including via break, goto, or return.
>
> The rest of the series converts manual rcu_read_lock()/
> rcu_read_unlock() and guard(rcu)() pairs across mm/, kernel/, fs/,
> lib/ and security/ to use the new macros.
>

Andrew - just a note (assuming Ye Liu is in agreement) I think all of the
below should be excluded from the cover letter that goes into the commit
message, including the checkpatch thing.

> Changes since v1 [1]:
>   - Rename macros from *_rcu to *_rculock, as suggested by Steven
>     Rostedt and acked by Thomas Gleixner, to avoid confusion with
>     existing *_rcu() list iterators that expect the caller to hold
>     the RCU read lock.
>   - Improve the comment on for_each_process_thread_rculock() to
>     document that 'break' only exits the inner loop and 'goto' is
>     needed to exit both loops (Thomas Gleixner).
>   - Rename the stale 'unlock:' label to 'out:' in hung_task.c, as
>     noted by Günther Noack.
>   - Clarify in patch 4 that page_pgoff() is safe outside the RCU
>     read-side critical section (SJ Park).
>   - CC all relevant maintainers on every patch (Lorenzo Stoakes).
>   - Drop the mm: prefix from patch 1, as the macros are in
>     include/linux/sched/signal.h (Michal Hocko).
>
> Patch 1 may trigger checkpatch "Macros with complex values should be
> enclosed in parentheses" errors.  These are false positives — the
> scoped_guard() pattern is a control-flow construct, not a multi-
> statement macro, and the same idiom is used elsewhere in the kernel.

While it's useful as a note to reviewers, in general checkpatch is taken
with a pinch of salt - it's a master of false positives so usually no need
to say this :)

>
> Suggested by Michal Hocko for the oom_kill path [2].
>
> [1] https://lore.kernel.org/all/20260904083001.553587-1-ye.liu@xxxxxxxxx/
> [2] https://lore.kernel.org/all/20260813092933.562028-1-ye.liu@xxxxxxxxx/
>
> Ye Liu (8):
>   sched: introduce for_each_process_rculock and for_each_thread_rculock
>   mm/oom_kill: convert process/thread iterators to for_each_*_rculock
>   mm/ksm: convert process iterator to for_each_process_rculock
>   mm/memory-failure: convert process iterator to for_each_process_rculock
>   kernel: convert process/thread iterators to for_each_*_rculock
>   fs: convert process/thread iterators to for_each_*_rculock
>   lib: convert process iterator to for_each_process_rculock
>   security/landlock: convert thread iterator to for_each_thread_rculock
>
>  fs/proc/base.c               |  4 +---
>  fs/resctrl/rdtgroup.c        |  8 ++------
>  include/linux/sched/signal.h | 25 +++++++++++++++++++++++++
>  kernel/cpu.c                 |  4 +---
>  kernel/freezer.c             |  4 +---
>  kernel/hung_task.c           | 11 ++++-------
>  kernel/locking/lockdep.c     |  4 +---
>  kernel/rcu/update.c          |  4 +---
>  kernel/sched/core.c          |  3 +--
>  kernel/sched/debug.c         |  4 +---
>  kernel/trace/fgraph.c        |  8 ++------
>  kernel/unwind/deferred.c     |  3 +--
>  lib/is_single_threaded.c     |  5 +----
>  mm/ksm.c                     |  4 +---
>  mm/memory-failure.c          | 16 ++++------------
>  mm/oom_kill.c                | 20 +++++---------------
>  security/landlock/tsync.c    |  8 ++------
>  17 files changed, 54 insertions(+), 81 deletions(-)
>
> Signed-off-by: Ye Liu <liuye@xxxxxxxxxx>
>
> --
> 2.25.1

--
Cheers, Lorenzo