[PATCH 0/8] mm: introduce for_each_process_rcu and for_each_thread_rcu

[PATCH 0/8] mm: introduce for_each_process_rcu and for_each_thread_rcu

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Introduce for_each_process_rcu(), for_each_thread_rcu() and
for_each_process_thread_rcu() 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.

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.

Suggested by Michal Hocko for the oom_kill path [1].

[1] https://lore.kernel.org/all/20260813092933.562028-1-ye.liu@linux.dev/

Ye Liu (8):
  mm: introduce for_each_process_rcu and for_each_thread_rcu
  mm/oom_kill: convert process/thread iterators to for_each_*_rcu
  mm/ksm: convert process iterator to for_each_process_rcu
  mm/memory-failure: convert process iterator to for_each_process_rcu
  kernel: convert process/thread iterators to for_each_*_rcu
  fs: convert process/thread iterators to for_each_*_rcu
  lib: convert process iterator to for_each_process_rcu
  security/landlock: convert thread iterator to for_each_thread_rcu

 fs/proc/base.c               |  4 +---
 fs/resctrl/rdtgroup.c        |  8 ++------
 include/linux/sched/signal.h | 19 +++++++++++++++++++
 kernel/cpu.c                 |  4 +---
 kernel/freezer.c             |  4 +---
 kernel/hung_task.c           |  7 ++-----
 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, 46 insertions(+), 79 deletions(-)

Signed-off-by: Ye Liu <liuye@kylinos.cn>

--
2.25.1

[PATCH 8/8] security/landlock: convert thread iterator to for_each_thread_rcu

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace guard(rcu)() + for_each_thread() with for_each_thread_rcu(),
so that the RCU read-side critical section is scoped to the loop body.

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 security/landlock/tsync.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/security/landlock/tsync.c b/security/landlock/tsync.c
index 0b71e158c3f5..f1c08aae179b 100644
--- a/security/landlock/tsync.c
+++ b/security/landlock/tsync.c
@@ -335,9 +335,7 @@ static size_t count_additional_threads(const struct tsync_works *works)
 
 	caller = current;
 
-	guard(rcu)();
-
-	for_each_thread(caller, thread) {
+	for_each_thread_rcu(caller, thread) {
 		/* Skip current, since it is initiating the sync. */
 		if (thread == caller)
 			continue;
@@ -376,9 +374,7 @@ static bool schedule_task_work(struct tsync_works *works,
 
 	caller = current;
 
-	guard(rcu)();
-
-	for_each_thread(caller, thread) {
+	for_each_thread_rcu(caller, thread) {
 		/* Skip current, since it is initiating the sync. */
 		if (thread == caller)
 			continue;
-- 
2.25.1

Re: [PATCH 8/8] security/landlock: convert thread iterator to for_each_thread_rcu

[Justin Suess]

On Fri, Sep 04, 2026 at 04:30:00PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace guard(rcu)() + for_each_thread() with for_each_thread_rcu(),
> so that the RCU read-side critical section is scoped to the loop body.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
>  security/landlock/tsync.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/security/landlock/tsync.c b/security/landlock/tsync.c
> index 0b71e158c3f5..f1c08aae179b 100644
> --- a/security/landlock/tsync.c
> +++ b/security/landlock/tsync.c
> @@ -335,9 +335,7 @@ static size_t count_additional_threads(const struct tsync_works *works)
>  
>  	caller = current;
>  
> -	guard(rcu)();
> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rcu(caller, thread) {
>  		/* Skip current, since it is initiating the sync. */
>  		if (thread == caller)
>  			continue;
> @@ -376,9 +374,7 @@ static bool schedule_task_work(struct tsync_works *works,
>  
>  	caller = current;
>  
> -	guard(rcu)();
> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rcu(caller, thread) {
>  		/* Skip current, since it is initiating the sync. */
>  		if (thread == caller)
>  			continue;

Reviewed-by: Justin Suess <utilityemal77@gmail.com>
> -- 
> 2.25.1
> 
> 

Re: [PATCH 8/8] security/landlock: convert thread iterator to for_each_thread_rcu

[Günther Noack]

On Fri, Sep 04, 2026 at 04:30:00PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace guard(rcu)() + for_each_thread() with for_each_thread_rcu(),
> so that the RCU read-side critical section is scoped to the loop body.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
>  security/landlock/tsync.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/security/landlock/tsync.c b/security/landlock/tsync.c
> index 0b71e158c3f5..f1c08aae179b 100644
> --- a/security/landlock/tsync.c
> +++ b/security/landlock/tsync.c
> @@ -335,9 +335,7 @@ static size_t count_additional_threads(const struct tsync_works *works)
>  
>  	caller = current;
>  
> -	guard(rcu)();
> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rcu(caller, thread) {
>  		/* Skip current, since it is initiating the sync. */
>  		if (thread == caller)
>  			continue;
> @@ -376,9 +374,7 @@ static bool schedule_task_work(struct tsync_works *works,
>  
>  	caller = current;
>  
> -	guard(rcu)();
> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rcu(caller, thread) {
>  		/* Skip current, since it is initiating the sync. */
>  		if (thread == caller)
>  			continue;
> -- 
> 2.25.1
> 

Reviewed-by: Günther Noack <gnoack3000@gmail.com>

Looks good, provided that the for_each_thread_rcu() macro gets
accepted.

Although, I find that in the Landlock case, it does not provide a very
strong advantage over the explicit "guard(rcu)();", and I find it
normally preferrable to use orthogonal APIs.

–Günther