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

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

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

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.

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.

Suggested by Michal Hocko for the oom_kill path [2].

[1] https://lore.kernel.org/all/20260904083001.553587-1-ye.liu@linux.dev/
[2] https://lore.kernel.org/all/20260813092933.562028-1-ye.liu@linux.dev/

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@kylinos.cn>

--
2.25.1

[PATCH v2 1/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Introduce for_each_process_rculock(), for_each_thread_rculock() and
for_each_process_thread_rculock() macros that acquire the RCU read
lock before the iteration starts and release it when the loop is left,
so that the RCU read-side critical section is scoped to the loop body
instead of an externally managed rcu_read_lock()/rcu_read_unlock()
pair.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
---
Changes in v2:
  - Rename macros from *_rcu to *_rculock (Steven Rostedt, Thomas Gleixner)
  - Improve comment on for_each_process_thread_rculock() double loop
  - Change prefix from mm: to sched: (Michal Hocko)
 include/linux/sched/signal.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 584ae88b435e..110ea9f131f3 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_SCHED_SIGNAL_H
 #define _LINUX_SCHED_SIGNAL_H
 
+#include <linux/cleanup.h>
 #include <linux/rculist.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
@@ -663,6 +664,30 @@ extern bool current_is_single_threaded(void);
 #define for_each_process_thread(p, t)	\
 	for_each_process(p) for_each_thread(p, t)
 
+/*
+ * Variants of for_each_process(), for_each_thread() and
+ * for_each_process_thread() that automatically acquire and release the
+ * RCU read lock via scoped_guard(rcu).  The lock is held for the
+ * duration of the loop and released on exit, including via break,
+ * goto, or return.
+ */
+#define for_each_process_rculock(p) \
+	scoped_guard(rcu) \
+	for (p = &init_task ; (p = next_task(p)) != &init_task ; )
+
+#define for_each_thread_rculock(p, t) \
+	scoped_guard(rcu) \
+	__for_each_thread((p)->signal, t)
+
+/*
+ * Double loop: 'break' only exits the inner for_each_thread() loop.
+ * Use 'goto' to exit both loops; the RCU read lock is released
+ * automatically when the scoped_guard scope is left.
+ */
+#define for_each_process_thread_rculock(p, t) \
+	scoped_guard(rcu) \
+	for_each_process(p) for_each_thread(p, t)
+
 typedef int (*proc_visitor)(struct task_struct *p, void *data);
 void walk_process_tree(struct task_struct *top, proc_visitor, void *);
 
-- 
2.25.1

[PATCH v2 2/8] mm/oom_kill: convert process/thread iterators to for_each_*_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() pairs wrapping
for_each_process()/for_each_thread() loops with for_each_process_rculock()
and for_each_thread_rculock(), which scope the RCU read lock to the
loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: SJ Park <sj@kernel.org>
---
Changes in v2:
  - Rename *_rcu to *_rculock
 mm/oom_kill.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5f372f6e26fa..ef2e1c423c1d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -94,8 +94,7 @@ static bool oom_cpuset_eligible(struct task_struct *start,
 	bool ret = false;
 	const nodemask_t *mask = oc->nodemask;
 
-	rcu_read_lock();
-	for_each_thread(start, tsk) {
+	for_each_thread_rculock(start, tsk) {
 		if (mask) {
 			/*
 			 * If this is a mempolicy constrained oom, tsk's
@@ -114,7 +113,6 @@ static bool oom_cpuset_eligible(struct task_struct *start,
 		if (ret)
 			break;
 	}
-	rcu_read_unlock();
 
 	return ret;
 }
@@ -368,11 +366,9 @@ static void select_bad_process(struct oom_control *oc)
 	else {
 		struct task_struct *p;
 
-		rcu_read_lock();
-		for_each_process(p)
+		for_each_process_rculock(p)
 			if (oom_evaluate_task(p, oc))
 				break;
-		rcu_read_unlock();
 	}
 }
 
@@ -430,14 +426,12 @@ static void dump_tasks(struct oom_control *oc)
 		struct task_struct *p;
 		int i = 0;
 
-		rcu_read_lock();
-		for_each_process(p) {
+		for_each_process_rculock(p) {
 			/* Avoid potential softlockup warning */
 			if ((++i & 1023) == 0)
 				touch_softlockup_watchdog();
 			dump_task(p, oc);
 		}
-		rcu_read_unlock();
 	}
 }
 
@@ -894,8 +888,7 @@ static bool task_will_free_mem(struct task_struct *task)
 	 * are dying as well to make sure that a) nobody pins its mm and
 	 * b) the task is also reapable by the oom reaper.
 	 */
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rculock(p) {
 		if (!process_shares_mm(p, mm))
 			continue;
 		if (same_thread_group(task, p))
@@ -904,7 +897,6 @@ static bool task_will_free_mem(struct task_struct *task)
 		if (!ret)
 			break;
 	}
-	rcu_read_unlock();
 
 	return ret;
 }
@@ -960,8 +952,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 	 * That thread will now get access to memory reserves since it has a
 	 * pending fatal signal.
 	 */
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rculock(p) {
 		if (!process_shares_mm(p, mm))
 			continue;
 		if (same_thread_group(p, victim))
@@ -982,7 +973,6 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 			continue;
 		do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
 	}
-	rcu_read_unlock();
 
 	if (can_oom_reap)
 		queue_oom_reaper(victim);
-- 
2.25.1

[PATCH v2 3/8] mm/ksm: convert process iterator to for_each_process_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
with for_each_process() loop in mm/ksm.c with for_each_process_rculock(),
which scopes the RCU read lock to the loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: SJ Park <sj@kernel.org>
---
Changes in v2:
  - Rename *_rcu to *_rculock
 mm/ksm.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 49d48d1e0998..69d30e80a090 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3280,8 +3280,7 @@ void collect_procs_ksm(const struct folio *folio, const struct page *page,
 		struct anon_vma *av = rmap_item->anon_vma;
 
 		anon_vma_lock_read(av);
-		rcu_read_lock();
-		for_each_process(tsk) {
+		for_each_process_rculock(tsk) {
 			struct anon_vma_chain *vmac;
 			const unsigned long addr = rmap_item->address & PAGE_MASK;
 			const unsigned long index = rmap_item->linear_page_index;
@@ -3298,7 +3297,6 @@ void collect_procs_ksm(const struct folio *folio, const struct page *page,
 				}
 			}
 		}
-		rcu_read_unlock();
 		anon_vma_unlock_read(av);
 	}
 }
-- 
2.25.1

[PATCH v2 4/8] mm/memory-failure: convert process iterator to for_each_process_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
with for_each_process() loop in mm/memory-failure.c with
for_each_process_rculock(), which scopes the RCU read lock to the
loop body via scoped_guard(rcu).

In collect_procs_file(), the page_pgoff() call now falls outside the
RCU read-side critical section.  This is safe because page_pgoff()
only reads folio->index and does not traverse any RCU-protected
structures.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
  - Clarify page_pgoff() safety outside RCU lock (SJ Park)
 mm/memory-failure.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a8b03e2920ba..7d93deb1f7b3 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -555,8 +555,7 @@ static void collect_procs_anon(const struct folio *folio,
 		return;
 
 	pgoff = page_pgoff(folio, page);
-	rcu_read_lock();
-	for_each_process(tsk) {
+	for_each_process_rculock(tsk) {
 		struct vm_area_struct *vma;
 		struct anon_vma_chain *vmac;
 		struct task_struct *t = task_early_kill(tsk, force_early);
@@ -572,7 +571,6 @@ static void collect_procs_anon(const struct folio *folio,
 			add_to_kill_anon_file(t, page, vma, to_kill, addr);
 		}
 	}
-	rcu_read_unlock();
 	anon_vma_unlock_read(av);
 }
 
@@ -589,9 +587,8 @@ static void collect_procs_file(const struct folio *folio,
 	pgoff_t pgoff;
 
 	i_mmap_lock_read(mapping);
-	rcu_read_lock();
 	pgoff = page_pgoff(folio, page);
-	for_each_process(tsk) {
+	for_each_process_rculock(tsk) {
 		struct task_struct *t = task_early_kill(tsk, force_early);
 		unsigned long addr;
 
@@ -611,7 +608,6 @@ static void collect_procs_file(const struct folio *folio,
 			add_to_kill_anon_file(t, page, vma, to_kill, addr);
 		}
 	}
-	rcu_read_unlock();
 	i_mmap_unlock_read(mapping);
 }
 
@@ -635,8 +631,7 @@ static void collect_procs_fsdax(const struct page *page,
 	struct task_struct *tsk;
 
 	i_mmap_lock_read(mapping);
-	rcu_read_lock();
-	for_each_process(tsk) {
+	for_each_process_rculock(tsk) {
 		struct task_struct *t = tsk;
 
 		/*
@@ -653,7 +648,6 @@ static void collect_procs_fsdax(const struct page *page,
 				add_to_kill_fsdax(t, page, vma, to_kill, pgoff);
 		}
 	}
-	rcu_read_unlock();
 	i_mmap_unlock_read(mapping);
 }
 #endif /* CONFIG_FS_DAX */
@@ -2288,8 +2282,7 @@ static void collect_procs_pfn(struct pfn_address_space *pfn_space,
 	struct address_space *mapping = pfn_space->mapping;
 
 	i_mmap_lock_read(mapping);
-	rcu_read_lock();
-	for_each_process(tsk) {
+	for_each_process_rculock(tsk) {
 		struct task_struct *t = tsk;
 
 		t = task_early_kill(tsk, true);
@@ -2303,7 +2296,6 @@ static void collect_procs_pfn(struct pfn_address_space *pfn_space,
 				add_to_kill_pgoff(t, vma, to_kill, pgoff);
 		}
 	}
-	rcu_read_unlock();
 	i_mmap_unlock_read(mapping);
 }
 
-- 
2.25.1

[PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
pairs combined with for_each_process(), for_each_thread() and
for_each_process_thread() loops across kernel/ with the
for_each_*_rculock() macros, which scope the RCU read lock to the
loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
  - Rename stale 'unlock:' label to 'out:' in hung_task.c (Günther Noack)
 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 +--
 9 files changed, 13 insertions(+), 32 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b3c8553d7bd6..00638d2abc0f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1254,8 +1254,7 @@ void clear_tasks_mm_cpumask(int cpu)
 	 * full-fledged tasklist_lock.
 	 */
 	WARN_ON(cpu_online(cpu));
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rculock(p) {
 		struct task_struct *t;
 
 		/*
@@ -1268,7 +1267,6 @@ void clear_tasks_mm_cpumask(int cpu)
 		arch_clear_mm_cpumask_cpu(cpu, t->mm);
 		task_unlock(t);
 	}
-	rcu_read_unlock();
 }
 
 /* Take this CPU down. */
diff --git a/kernel/freezer.c b/kernel/freezer.c
index a76bf957fb32..7a870f71dcf6 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -217,11 +217,9 @@ void thaw_process(struct task_struct *p)
 {
 	struct task_struct *t;
 
-	rcu_read_lock();
-	for_each_thread(p, t) {
+	for_each_thread_rculock(p, t) {
 		__thaw_task(t);
 	}
-	rcu_read_unlock();
 }
 
 /**
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 6fcc94ce4ca9..73a5ad3be9a8 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 		return;
 
 	this_round_count = 0;
-	rcu_read_lock();
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rculock(g, t) {
 		if (!max_count--)
-			goto unlock;
+			goto out;
 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 			if (!rcu_lock_break(g, t))
-				goto unlock;
+				goto out;
 			last_break = jiffies;
 		}
 
@@ -337,9 +336,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 			hung_task_info(t, timeout, this_round_count);
 		}
 	}
- unlock:
-	rcu_read_unlock();
-
+out:
 	if (!this_round_count)
 		return;
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c56a7f91d72e..ea218dc75ad5 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6834,15 +6834,13 @@ void debug_show_all_locks(void)
 	}
 	pr_warn("\nShowing all locks held in the system:\n");
 
-	rcu_read_lock();
-	for_each_process_thread(g, p) {
+	for_each_process_thread_rculock(g, p) {
 		if (!p->lockdep_depth)
 			continue;
 		lockdep_print_held_locks(p);
 		touch_nmi_watchdog();
 		touch_all_softlockup_watchdogs();
 	}
-	rcu_read_unlock();
 
 	pr_warn("\n");
 	pr_warn("=============================================\n\n");
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 2a778b8ab4ad..d8e0b5896db9 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -548,15 +548,13 @@ void synchronize_rcu_trivial_preempt(void)
 	struct task_struct *t;
 
 	smp_mb(); // Order prior accesses before grace-period start.
-	rcu_read_lock(); // Protect task list.
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rculock(g, t) {
 		if (t == current)
 			continue;  // Don't deadlock on ourselves!
 		// Order later rcu_read_lock() on other tasks after QS.
 		while (smp_load_acquire(&t->rcu_trivial_preempt_nesting))
 			continue;
 	}
-	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_trivial_preempt);
 #endif // #if IS_ENABLED(CONFIG_TRIVIAL_PREEMPT_RCU)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0697ed0f1c3d..fd5bdd2cb798 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2005,8 +2005,7 @@ static void uclamp_sync_util_min_rt_default(void)
 	smp_mb__after_spinlock();
 	read_unlock(&tasklist_lock);
 
-	guard(rcu)();
-	for_each_process_thread(g, p)
+	for_each_process_thread_rculock(g, p)
 		uclamp_update_util_min_rt_default(p);
 }
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 72236db67983..cdae165b98f7 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1029,14 +1029,12 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 #endif
 		   "\n");
 
-	rcu_read_lock();
-	for_each_process_thread(g, p) {
+	for_each_process_thread_rculock(g, p) {
 		if (task_cpu(p) != rq_cpu)
 			continue;
 
 		print_task(m, rq, p);
 	}
-	rcu_read_unlock();
 }
 
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 40d373d65f9b..f797ce119223 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1057,11 +1057,10 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
 		}
 	}
 
-	rcu_read_lock();
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rculock(g, t) {
 		if (start == end) {
 			ret = -EAGAIN;
-			goto unlock;
+			goto free;
 		}
 
 		if (t->ret_stack == NULL) {
@@ -1074,9 +1073,6 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
 			t->ret_stack = ret_stack_list[start++];
 		}
 	}
-
-unlock:
-	rcu_read_unlock();
 free:
 	for (i = start; i < end; i++)
 		kmem_cache_free(fgraph_stack_cachep, ret_stack_list[i]);
diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c
index 5bea47314254..ecfe1336095e 100644
--- a/kernel/unwind/deferred.c
+++ b/kernel/unwind/deferred.c
@@ -319,9 +319,8 @@ void unwind_deferred_cancel(struct unwind_work *work)
 
 	synchronize_srcu(&unwind_srcu);
 
-	guard(rcu)();
 	/* Clear this bit from all threads */
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rculock(g, t) {
 		atomic_long_andnot(BIT(bit),
 				   &t->unwind_info.unwind_mask);
 		if (t->unwind_info.cache)
-- 
2.25.1

[PATCH v2 6/8] fs: convert process/thread iterators to for_each_*_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
with for_each_process() and for_each_process_thread() loops in fs/
with the for_each_*_rculock() macros, which scope the RCU read lock
to the loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
 fs/proc/base.c        | 4 +---
 fs/resctrl/rdtgroup.c | 8 ++------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6a39de424f62..3de4f4557e4c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1160,8 +1160,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
 	if (mm) {
 		struct task_struct *p;
 
-		rcu_read_lock();
-		for_each_process(p) {
+		for_each_process_rculock(p) {
 			if (same_thread_group(task, p))
 				continue;
 
@@ -1177,7 +1176,6 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
 			}
 			task_unlock(p);
 		}
-		rcu_read_unlock();
 		mmdrop(mm);
 	}
 err_unlock:
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5dcbb0a964e8..b14df8b23f1a 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -709,14 +709,12 @@ int rdtgroup_tasks_assigned(struct rdtgroup *r)
 
 	lockdep_assert_held(&rdtgroup_mutex);
 
-	rcu_read_lock();
-	for_each_process_thread(p, t) {
+	for_each_process_thread_rculock(p, t) {
 		if (is_closid_match(t, r) || is_rmid_match(t, r)) {
 			ret = 1;
 			break;
 		}
 	}
-	rcu_read_unlock();
 
 	return ret;
 }
@@ -826,15 +824,13 @@ static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
 	struct task_struct *p, *t;
 	pid_t pid;
 
-	rcu_read_lock();
-	for_each_process_thread(p, t) {
+	for_each_process_thread_rculock(p, t) {
 		if (is_closid_match(t, r) || is_rmid_match(t, r)) {
 			pid = task_pid_vnr(t);
 			if (pid)
 				seq_printf(s, "%d\n", pid);
 		}
 	}
-	rcu_read_unlock();
 }
 
 static int rdtgroup_tasks_show(struct kernfs_open_file *of,
-- 
2.25.1

[PATCH v2 7/8] lib: convert process iterator to for_each_process_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
with for_each_process() loop in lib/ with for_each_process_rculock(),
which scopes the RCU read lock to the loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Acked-by: Michal Hocko <mhocko@suse.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
 lib/is_single_threaded.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index 8c98b20bfc41..4e7fe85454ab 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -26,8 +26,7 @@ bool current_is_single_threaded(void)
 		return true;
 
 	ret = false;
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rculock(p) {
 		if (unlikely(p->flags & PF_KTHREAD))
 			continue;
 		if (unlikely(p == task->group_leader))
@@ -48,7 +47,5 @@ bool current_is_single_threaded(void)
 	}
 	ret = true;
 found:
-	rcu_read_unlock();
-
 	return ret;
 }
-- 
2.25.1

[PATCH v2 8/8] security/landlock: convert thread iterator to for_each_thread_rculock

[Ye Liu]

From: Ye Liu <liuye@kylinos.cn>

Replace guard(rcu)() + for_each_thread() with for_each_thread_rculock(),
which scopes the RCU read lock to the loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
Reviewed-by: Justin Suess <utilityemal77@gmail.com>
Reviewed-by: Günther Noack <gnoack3000@gmail.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
 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..a578af640aad 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_rculock(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_rculock(caller, thread) {
 		/* Skip current, since it is initiating the sync. */
 		if (thread == caller)
 			continue;
-- 
2.25.1

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@kylinos.cn>
>
> 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@linux.dev/
> [2] https://lore.kernel.org/all/20260813092933.562028-1-ye.liu@linux.dev/
>
> 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@kylinos.cn>
>
> --
> 2.25.1

--
Cheers, Lorenzo

Re: [PATCH v2 1/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:27PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Introduce for_each_process_rculock(), for_each_thread_rculock() and
> for_each_process_thread_rculock() macros that acquire the RCU read
> lock before the iteration starts and release it when the loop is left,
> so that the RCU read-side critical section is scoped to the loop body
> instead of an externally managed rcu_read_lock()/rcu_read_unlock()
> pair.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Some nits below, with those addressed, LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename macros from *_rcu to *_rculock (Steven Rostedt, Thomas Gleixner)
>   - Improve comment on for_each_process_thread_rculock() double loop
>   - Change prefix from mm: to sched: (Michal Hocko)
>  include/linux/sched/signal.h | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> index 584ae88b435e..110ea9f131f3 100644
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -2,6 +2,7 @@
>  #ifndef _LINUX_SCHED_SIGNAL_H
>  #define _LINUX_SCHED_SIGNAL_H
>
> +#include <linux/cleanup.h>
>  #include <linux/rculist.h>
>  #include <linux/signal.h>
>  #include <linux/sched.h>
> @@ -663,6 +664,30 @@ extern bool current_is_single_threaded(void);
>  #define for_each_process_thread(p, t)	\
>  	for_each_process(p) for_each_thread(p, t)
>
> +/*
> + * Variants of for_each_process(), for_each_thread() and
> + * for_each_process_thread() that automatically acquire and release the
> + * RCU read lock via scoped_guard(rcu).  The lock is held for the
> + * duration of the loop and released on exit, including via break,
> + * goto, or return.
> + */
> +#define for_each_process_rculock(p) \
> +	scoped_guard(rcu) \
> +	for (p = &init_task ; (p = next_task(p)) != &init_task ; )

NIT: Can you indent the for loop by a tab? Since the for is in
scoped_guard() scope and that's not made clear.

> +
> +#define for_each_thread_rculock(p, t) \
> +	scoped_guard(rcu) \
> +	__for_each_thread((p)->signal, t)

Same comment as above.

> +
> +/*
> + * Double loop: 'break' only exits the inner for_each_thread() loop.
> + * Use 'goto' to exit both loops; the RCU read lock is released
> + * automatically when the scoped_guard scope is left.
> + */
> +#define for_each_process_thread_rculock(p, t) \
> +	scoped_guard(rcu) \
> +	for_each_process(p) for_each_thread(p, t)

Yeah this is even worse for clarity :) I know the existing defines do itg
this way but it's kinda confusing.

I know it's a bit fugly, but it's MUCH clearer as:

	#define for_each_process_thread_rculock(p, t) \
		scoped_guard(rcu) \
			for_each_process(p) \
				for_each_thread(p, t)

> +
>  typedef int (*proc_visitor)(struct task_struct *p, void *data);
>  void walk_process_tree(struct task_struct *top, proc_visitor, void *);
>
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 2/8] mm/oom_kill: convert process/thread iterators to for_each_*_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:28PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs wrapping
> for_each_process()/for_each_thread() loops with for_each_process_rculock()
> and for_each_thread_rculock(), which scope the RCU read lock to the
> loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: SJ Park <sj@kernel.org>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>  mm/oom_kill.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5f372f6e26fa..ef2e1c423c1d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -94,8 +94,7 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  	bool ret = false;
>  	const nodemask_t *mask = oc->nodemask;
>
> -	rcu_read_lock();
> -	for_each_thread(start, tsk) {
> +	for_each_thread_rculock(start, tsk) {
>  		if (mask) {
>  			/*
>  			 * If this is a mempolicy constrained oom, tsk's
> @@ -114,7 +113,6 @@ static bool oom_cpuset_eligible(struct task_struct *start,
>  		if (ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>
>  	return ret;
>  }
> @@ -368,11 +366,9 @@ static void select_bad_process(struct oom_control *oc)
>  	else {
>  		struct task_struct *p;
>
> -		rcu_read_lock();
> -		for_each_process(p)
> +		for_each_process_rculock(p)
>  			if (oom_evaluate_task(p, oc))
>  				break;
> -		rcu_read_unlock();
>  	}
>  }
>
> @@ -430,14 +426,12 @@ static void dump_tasks(struct oom_control *oc)
>  		struct task_struct *p;
>  		int i = 0;
>
> -		rcu_read_lock();
> -		for_each_process(p) {
> +		for_each_process_rculock(p) {
>  			/* Avoid potential softlockup warning */
>  			if ((++i & 1023) == 0)
>  				touch_softlockup_watchdog();
>  			dump_task(p, oc);
>  		}
> -		rcu_read_unlock();
>  	}
>  }
>
> @@ -894,8 +888,7 @@ static bool task_will_free_mem(struct task_struct *task)
>  	 * are dying as well to make sure that a) nobody pins its mm and
>  	 * b) the task is also reapable by the oom reaper.
>  	 */
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rculock(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
>  		if (same_thread_group(task, p))
> @@ -904,7 +897,6 @@ static bool task_will_free_mem(struct task_struct *task)
>  		if (!ret)
>  			break;
>  	}
> -	rcu_read_unlock();
>
>  	return ret;
>  }
> @@ -960,8 +952,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  	 * That thread will now get access to memory reserves since it has a
>  	 * pending fatal signal.
>  	 */
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rculock(p) {
>  		if (!process_shares_mm(p, mm))
>  			continue;
>  		if (same_thread_group(p, victim))
> @@ -982,7 +973,6 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  			continue;
>  		do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
>  	}
> -	rcu_read_unlock();
>
>  	if (can_oom_reap)
>  		queue_oom_reaper(victim);
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 3/8] mm/ksm: convert process iterator to for_each_process_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:29PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in mm/ksm.c with for_each_process_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: SJ Park <sj@kernel.org>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>  mm/ksm.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 49d48d1e0998..69d30e80a090 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -3280,8 +3280,7 @@ void collect_procs_ksm(const struct folio *folio, const struct page *page,
>  		struct anon_vma *av = rmap_item->anon_vma;
>
>  		anon_vma_lock_read(av);
> -		rcu_read_lock();
> -		for_each_process(tsk) {
> +		for_each_process_rculock(tsk) {
>  			struct anon_vma_chain *vmac;
>  			const unsigned long addr = rmap_item->address & PAGE_MASK;
>  			const unsigned long index = rmap_item->linear_page_index;
> @@ -3298,7 +3297,6 @@ void collect_procs_ksm(const struct folio *folio, const struct page *page,
>  				}
>  			}
>  		}
> -		rcu_read_unlock();
>  		anon_vma_unlock_read(av);
>  	}
>  }
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 1/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Oleg Nesterov]

On 09/07, Ye Liu wrote:
>
> Introduce for_each_process_rculock(), for_each_thread_rculock() and
> for_each_process_thread_rculock() macros that acquire the RCU read
> lock before the iteration starts and release it when the loop is left,
> so that the RCU read-side critical section is scoped to the loop body
> instead of an externally managed rcu_read_lock()/rcu_read_unlock()
> pair.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks, I personally like the new _rculock suffix more ;)

I see the comments about indentation from Lorenzo, I am fine either way.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>

Re: [PATCH v2 4/8] mm/memory-failure: convert process iterator to for_each_process_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:30PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() loop in mm/memory-failure.c with
> for_each_process_rculock(), which scopes the RCU read lock to the
> loop body via scoped_guard(rcu).
>
> In collect_procs_file(), the page_pgoff() call now falls outside the
> RCU read-side critical section.  This is safe because page_pgoff()
> only reads folio->index and does not traverse any RCU-protected
> structures.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Miaohe Lin <linmiaohe@huawei.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>   - Clarify page_pgoff() safety outside RCU lock (SJ Park)
>  mm/memory-failure.c | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index a8b03e2920ba..7d93deb1f7b3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -555,8 +555,7 @@ static void collect_procs_anon(const struct folio *folio,
>  		return;
>
>  	pgoff = page_pgoff(folio, page);
> -	rcu_read_lock();
> -	for_each_process(tsk) {
> +	for_each_process_rculock(tsk) {
>  		struct vm_area_struct *vma;
>  		struct anon_vma_chain *vmac;
>  		struct task_struct *t = task_early_kill(tsk, force_early);
> @@ -572,7 +571,6 @@ static void collect_procs_anon(const struct folio *folio,
>  			add_to_kill_anon_file(t, page, vma, to_kill, addr);
>  		}
>  	}
> -	rcu_read_unlock();
>  	anon_vma_unlock_read(av);
>  }
>
> @@ -589,9 +587,8 @@ static void collect_procs_file(const struct folio *folio,
>  	pgoff_t pgoff;
>
>  	i_mmap_lock_read(mapping);
> -	rcu_read_lock();
>  	pgoff = page_pgoff(folio, page);
> -	for_each_process(tsk) {
> +	for_each_process_rculock(tsk) {
>  		struct task_struct *t = task_early_kill(tsk, force_early);
>  		unsigned long addr;
>
> @@ -611,7 +608,6 @@ static void collect_procs_file(const struct folio *folio,
>  			add_to_kill_anon_file(t, page, vma, to_kill, addr);
>  		}
>  	}
> -	rcu_read_unlock();
>  	i_mmap_unlock_read(mapping);
>  }
>
> @@ -635,8 +631,7 @@ static void collect_procs_fsdax(const struct page *page,
>  	struct task_struct *tsk;
>
>  	i_mmap_lock_read(mapping);
> -	rcu_read_lock();
> -	for_each_process(tsk) {
> +	for_each_process_rculock(tsk) {
>  		struct task_struct *t = tsk;
>
>  		/*
> @@ -653,7 +648,6 @@ static void collect_procs_fsdax(const struct page *page,
>  				add_to_kill_fsdax(t, page, vma, to_kill, pgoff);
>  		}
>  	}
> -	rcu_read_unlock();
>  	i_mmap_unlock_read(mapping);
>  }
>  #endif /* CONFIG_FS_DAX */
> @@ -2288,8 +2282,7 @@ static void collect_procs_pfn(struct pfn_address_space *pfn_space,
>  	struct address_space *mapping = pfn_space->mapping;
>
>  	i_mmap_lock_read(mapping);
> -	rcu_read_lock();
> -	for_each_process(tsk) {
> +	for_each_process_rculock(tsk) {
>  		struct task_struct *t = tsk;
>
>  		t = task_early_kill(tsk, true);
> @@ -2303,7 +2296,6 @@ static void collect_procs_pfn(struct pfn_address_space *pfn_space,
>  				add_to_kill_pgoff(t, vma, to_kill, pgoff);
>  		}
>  	}
> -	rcu_read_unlock();
>  	i_mmap_unlock_read(mapping);
>  }
>
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
> pairs combined with for_each_process(), for_each_thread() and
> for_each_process_thread() loops across kernel/ with the
> for_each_*_rculock() macros, which scope the RCU read lock to the
> loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>   - Rename stale 'unlock:' label to 'out:' in hung_task.c (Günther Noack)
>  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 +--
>  9 files changed, 13 insertions(+), 32 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index b3c8553d7bd6..00638d2abc0f 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1254,8 +1254,7 @@ void clear_tasks_mm_cpumask(int cpu)
>  	 * full-fledged tasklist_lock.
>  	 */
>  	WARN_ON(cpu_online(cpu));
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rculock(p) {
>  		struct task_struct *t;
>
>  		/*
> @@ -1268,7 +1267,6 @@ void clear_tasks_mm_cpumask(int cpu)
>  		arch_clear_mm_cpumask_cpu(cpu, t->mm);
>  		task_unlock(t);
>  	}
> -	rcu_read_unlock();
>  }
>
>  /* Take this CPU down. */
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index a76bf957fb32..7a870f71dcf6 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -217,11 +217,9 @@ void thaw_process(struct task_struct *p)
>  {
>  	struct task_struct *t;
>
> -	rcu_read_lock();
> -	for_each_thread(p, t) {
> +	for_each_thread_rculock(p, t) {
>  		__thaw_task(t);
>  	}
> -	rcu_read_unlock();
>  }
>
>  /**
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 6fcc94ce4ca9..73a5ad3be9a8 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  		return;
>
>  	this_round_count = 0;
> -	rcu_read_lock();
> -	for_each_process_thread(g, t) {
> +	for_each_process_thread_rculock(g, t) {
>  		if (!max_count--)
> -			goto unlock;
> +			goto out;
>  		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
>  			if (!rcu_lock_break(g, t))
> -				goto unlock;
> +				goto out;
>  			last_break = jiffies;
>  		}
>
> @@ -337,9 +336,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  			hung_task_info(t, timeout, this_round_count);
>  		}
>  	}
> - unlock:
> -	rcu_read_unlock();
> -
> +out:
>  	if (!this_round_count)
>  		return;
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c56a7f91d72e..ea218dc75ad5 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -6834,15 +6834,13 @@ void debug_show_all_locks(void)
>  	}
>  	pr_warn("\nShowing all locks held in the system:\n");
>
> -	rcu_read_lock();
> -	for_each_process_thread(g, p) {
> +	for_each_process_thread_rculock(g, p) {
>  		if (!p->lockdep_depth)
>  			continue;
>  		lockdep_print_held_locks(p);
>  		touch_nmi_watchdog();
>  		touch_all_softlockup_watchdogs();
>  	}
> -	rcu_read_unlock();
>
>  	pr_warn("\n");
>  	pr_warn("=============================================\n\n");
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index 2a778b8ab4ad..d8e0b5896db9 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -548,15 +548,13 @@ void synchronize_rcu_trivial_preempt(void)
>  	struct task_struct *t;
>
>  	smp_mb(); // Order prior accesses before grace-period start.
> -	rcu_read_lock(); // Protect task list.
> -	for_each_process_thread(g, t) {
> +	for_each_process_thread_rculock(g, t) {
>  		if (t == current)
>  			continue;  // Don't deadlock on ourselves!
>  		// Order later rcu_read_lock() on other tasks after QS.
>  		while (smp_load_acquire(&t->rcu_trivial_preempt_nesting))
>  			continue;
>  	}
> -	rcu_read_unlock();
>  }
>  EXPORT_SYMBOL_GPL(synchronize_rcu_trivial_preempt);
>  #endif // #if IS_ENABLED(CONFIG_TRIVIAL_PREEMPT_RCU)
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0697ed0f1c3d..fd5bdd2cb798 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2005,8 +2005,7 @@ static void uclamp_sync_util_min_rt_default(void)
>  	smp_mb__after_spinlock();
>  	read_unlock(&tasklist_lock);
>
> -	guard(rcu)();
> -	for_each_process_thread(g, p)
> +	for_each_process_thread_rculock(g, p)
>  		uclamp_update_util_min_rt_default(p);
>  }
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 72236db67983..cdae165b98f7 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -1029,14 +1029,12 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
>  #endif
>  		   "\n");
>
> -	rcu_read_lock();
> -	for_each_process_thread(g, p) {
> +	for_each_process_thread_rculock(g, p) {
>  		if (task_cpu(p) != rq_cpu)
>  			continue;
>
>  		print_task(m, rq, p);
>  	}
> -	rcu_read_unlock();
>  }
>
>  void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 40d373d65f9b..f797ce119223 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1057,11 +1057,10 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
>  		}
>  	}
>
> -	rcu_read_lock();
> -	for_each_process_thread(g, t) {
> +	for_each_process_thread_rculock(g, t) {
>  		if (start == end) {
>  			ret = -EAGAIN;
> -			goto unlock;
> +			goto free;
>  		}
>
>  		if (t->ret_stack == NULL) {
> @@ -1074,9 +1073,6 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
>  			t->ret_stack = ret_stack_list[start++];
>  		}
>  	}
> -
> -unlock:
> -	rcu_read_unlock();
>  free:
>  	for (i = start; i < end; i++)
>  		kmem_cache_free(fgraph_stack_cachep, ret_stack_list[i]);
> diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c
> index 5bea47314254..ecfe1336095e 100644
> --- a/kernel/unwind/deferred.c
> +++ b/kernel/unwind/deferred.c
> @@ -319,9 +319,8 @@ void unwind_deferred_cancel(struct unwind_work *work)
>
>  	synchronize_srcu(&unwind_srcu);
>
> -	guard(rcu)();
>  	/* Clear this bit from all threads */
> -	for_each_process_thread(g, t) {
> +	for_each_process_thread_rculock(g, t) {
>  		atomic_long_andnot(BIT(bit),
>  				   &t->unwind_info.unwind_mask);
>  		if (t->unwind_info.cache)
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 6/8] fs: convert process/thread iterators to for_each_*_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:32PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() and for_each_process_thread() loops in fs/
> with the for_each_*_rculock() macros, which scope the RCU read lock
> to the loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>  fs/proc/base.c        | 4 +---
>  fs/resctrl/rdtgroup.c | 8 ++------
>  2 files changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 6a39de424f62..3de4f4557e4c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1160,8 +1160,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
>  	if (mm) {
>  		struct task_struct *p;
>
> -		rcu_read_lock();
> -		for_each_process(p) {
> +		for_each_process_rculock(p) {
>  			if (same_thread_group(task, p))
>  				continue;
>
> @@ -1177,7 +1176,6 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
>  			}
>  			task_unlock(p);
>  		}
> -		rcu_read_unlock();
>  		mmdrop(mm);
>  	}
>  err_unlock:
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 5dcbb0a964e8..b14df8b23f1a 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -709,14 +709,12 @@ int rdtgroup_tasks_assigned(struct rdtgroup *r)
>
>  	lockdep_assert_held(&rdtgroup_mutex);
>
> -	rcu_read_lock();
> -	for_each_process_thread(p, t) {
> +	for_each_process_thread_rculock(p, t) {
>  		if (is_closid_match(t, r) || is_rmid_match(t, r)) {
>  			ret = 1;
>  			break;
>  		}
>  	}
> -	rcu_read_unlock();
>
>  	return ret;
>  }
> @@ -826,15 +824,13 @@ static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
>  	struct task_struct *p, *t;
>  	pid_t pid;
>
> -	rcu_read_lock();
> -	for_each_process_thread(p, t) {
> +	for_each_process_thread_rculock(p, t) {
>  		if (is_closid_match(t, r) || is_rmid_match(t, r)) {
>  			pid = task_pid_vnr(t);
>  			if (pid)
>  				seq_printf(s, "%d\n", pid);
>  		}
>  	}
> -	rcu_read_unlock();
>  }
>
>  static int rdtgroup_tasks_show(struct kernfs_open_file *of,
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 7/8] lib: convert process iterator to for_each_process_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:33PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in lib/ with for_each_process_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>  lib/is_single_threaded.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
> index 8c98b20bfc41..4e7fe85454ab 100644
> --- a/lib/is_single_threaded.c
> +++ b/lib/is_single_threaded.c
> @@ -26,8 +26,7 @@ bool current_is_single_threaded(void)
>  		return true;
>
>  	ret = false;
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rculock(p) {
>  		if (unlikely(p->flags & PF_KTHREAD))
>  			continue;
>  		if (unlikely(p == task->group_leader))
> @@ -48,7 +47,5 @@ bool current_is_single_threaded(void)
>  	}
>  	ret = true;
>  found:
> -	rcu_read_unlock();
> -
>  	return ret;
>  }
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 8/8] security/landlock: convert thread iterator to for_each_thread_rculock

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 04:13:34PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
>
> Replace guard(rcu)() + for_each_thread() with for_each_thread_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Reviewed-by: Justin Suess <utilityemal77@gmail.com>
> Reviewed-by: Günther Noack <gnoack3000@gmail.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> Changes in v2:
>   - Rename *_rcu to *_rculock
>  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..a578af640aad 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)();

OK looked at the file and confirmed the function exits just after the below
section so fine :)

> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rculock(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)();

Similar here.

> -
> -	for_each_thread(caller, thread) {
> +	for_each_thread_rculock(caller, thread) {
>  		/* Skip current, since it is initiating the sync. */
>  		if (thread == caller)
>  			continue;
> --
> 2.25.1
>

--
Cheers, Lorenzo

Re: [PATCH v2 1/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:27PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Introduce for_each_process_rculock(), for_each_thread_rculock() and
> for_each_process_thread_rculock() macros that acquire the RCU read
> lock before the iteration starts and release it when the loop is left,
> so that the RCU read-side critical section is scoped to the loop body
> instead of an externally managed rcu_read_lock()/rcu_read_unlock()
> pair.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Lorenzo already picked up the nits, this is really nice otherwise.

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 2/8] mm/oom_kill: convert process/thread iterators to for_each_*_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:28PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs wrapping
> for_each_process()/for_each_thread() loops with for_each_process_rculock()
> and for_each_thread_rculock(), which scope the RCU read lock to the
> loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: SJ Park <sj@kernel.org>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 3/8] mm/ksm: convert process iterator to for_each_process_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:29PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in mm/ksm.c with for_each_process_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: SJ Park <sj@kernel.org>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 4/8] mm/memory-failure: convert process iterator to for_each_process_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:30PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() loop in mm/memory-failure.c with
> for_each_process_rculock(), which scopes the RCU read lock to the
> loop body via scoped_guard(rcu).
> 
> In collect_procs_file(), the page_pgoff() call now falls outside the
> RCU read-side critical section.  This is safe because page_pgoff()
> only reads folio->index and does not traverse any RCU-protected
> structures.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Miaohe Lin <linmiaohe@huawei.com>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 6/8] fs: convert process/thread iterators to for_each_*_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:32PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() and for_each_process_thread() loops in fs/
> with the for_each_*_rculock() macros, which scope the RCU read lock
> to the loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 7/8] lib: convert process iterator to for_each_process_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:33PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in lib/ with for_each_process_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 8/8] security/landlock: convert thread iterator to for_each_thread_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:34PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace guard(rcu)() + for_each_thread() with for_each_thread_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Reviewed-by: Justin Suess <utilityemal77@gmail.com>
> Reviewed-by: Günther Noack <gnoack3000@gmail.com>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
> pairs combined with for_each_process(), for_each_thread() and
> for_each_process_thread() loops across kernel/ with the
> for_each_*_rculock() macros, which scope the RCU read lock to the
> loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Question below

> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 6fcc94ce4ca9..73a5ad3be9a8 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  		return;
>  
>  	this_round_count = 0;
> -	rcu_read_lock();
> -	for_each_process_thread(g, t) {
> +	for_each_process_thread_rculock(g, t) {
>  		if (!max_count--)
> -			goto unlock;
> +			goto out;
... snip ...
> - unlock:
> -	rcu_read_unlock();
> -
> +out:
>  	if (!this_round_count)
>  		return;
>  

The sunken rcu_read_lock()/unlock() + scoped_guard usage makes this goto
at a minimum very confusing, if not actually broken.

Are we sure this isn't broken as-written? Generally we don't mix cleanup
and goto for exactly this reason.

~Gregory

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Oleg Nesterov]

On 09/07, Gregory Price wrote:
>
> On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> >  		return;
> >
> >  	this_round_count = 0;
> > -	rcu_read_lock();
> > -	for_each_process_thread(g, t) {
> > +	for_each_process_thread_rculock(g, t) {
> >  		if (!max_count--)
> > -			goto unlock;
> > +			goto out;
> ... snip ...
> > - unlock:
> > -	rcu_read_unlock();
> > -
> > +out:
> >  	if (!this_round_count)
> >  		return;
> >
>
> The sunken rcu_read_lock()/unlock() + scoped_guard usage makes this goto
> at a minimum very confusing, if not actually broken.

I am afraid I misunderstood you concerns...

This patch renames the "unlock:" label to "out:", and to me this makes sense.

Unfortunately for_each_process_thread() and the new helper can't use "break".

Oleg.

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Gregory Price]

On Mon, Sep 07, 2026 at 07:57:15PM +0200, Oleg Nesterov wrote:
> On 09/07, Gregory Price wrote:
> >
> > On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> > > --- a/kernel/hung_task.c
> > > +++ b/kernel/hung_task.c
> > > @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > >  		return;
> > >
> > >  	this_round_count = 0;
> > > -	rcu_read_lock();
> > > -	for_each_process_thread(g, t) {
> > > +	for_each_process_thread_rculock(g, t) {
> > >  		if (!max_count--)
> > > -			goto unlock;
> > > +			goto out;
> > ... snip ...
> > > - unlock:
> > > -	rcu_read_unlock();
> > > -
> > > +out:
> > >  	if (!this_round_count)
> > >  		return;
> > >
> >
> > The sunken rcu_read_lock()/unlock() + scoped_guard usage makes this goto
> > at a minimum very confusing, if not actually broken.
> 
> I am afraid I misunderstood you concerns...
>

This might be my - admittedly shallow - understanding of scoped_guard,
but does scoped guard handle goto correctly?

On the surface it looks like it would skip the unlock entirely.

That is what i mean by "at a minimum very confusing, if not broken"
and why it's generally discouraged to mix cleanup.h and goto.

~Gregory

Re: [PATCH v2 1/8] sched: introduce for_each_process_rculock and for_each_thread_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:27 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Introduce for_each_process_rculock(), for_each_thread_rculock() and
> for_each_process_thread_rculock() macros that acquire the RCU read
> lock before the iteration starts and release it when the loop is left,
> so that the RCU read-side critical section is scoped to the loop body
> instead of an externally managed rcu_read_lock()/rcu_read_unlock()
> pair.

Looks good to me.

> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Assuming Lorenzo's indentation change requests are accepted,

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 4/8] mm/memory-failure: convert process iterator to for_each_process_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:30 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() loop in mm/memory-failure.c with
> for_each_process_rculock(), which scopes the RCU read lock to the
> loop body via scoped_guard(rcu).
> 
> In collect_procs_file(), the page_pgoff() call now falls outside the
> RCU read-side critical section.  This is safe because page_pgoff()
> only reads folio->index and does not traverse any RCU-protected
> structures.

Thank you for clarifying :)

> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Miaohe Lin <linmiaohe@huawei.com>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:31 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
> pairs combined with for_each_process(), for_each_thread() and
> for_each_process_thread() loops across kernel/ with the
> for_each_*_rculock() macros, which scope the RCU read lock to the
> loop body via scoped_guard(rcu).
> 
> No functional change.

Looks good and correct to me.

> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 6/8] fs: convert process/thread iterators to for_each_*_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:32 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pairs combined
> with for_each_process() and for_each_process_thread() loops in fs/
> with the for_each_*_rculock() macros, which scope the RCU read lock
> to the loop body via scoped_guard(rcu).
> 
> No functional change.

Looks good and correct to me.

> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 7/8] lib: convert process iterator to for_each_process_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:33 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in lib/ with for_each_process_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
> 
> No functional change.

Looks good and correct to me.

> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 8/8] security/landlock: convert thread iterator to for_each_thread_rculock

[SJ Park]

On Mon,  7 Sep 2026 16:13:34 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> From: Ye Liu <liuye@kylinos.cn>
> 
> Replace guard(rcu)() + for_each_thread() with for_each_thread_rculock(),
> which scopes the RCU read lock to the loop body via scoped_guard(rcu).
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> Reviewed-by: Justin Suess <utilityemal77@gmail.com>
> Reviewed-by: Günther Noack <gnoack3000@gmail.com>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Oleg Nesterov]

On 09/07, Gregory Price wrote:
>
> On Mon, Sep 07, 2026 at 07:57:15PM +0200, Oleg Nesterov wrote:
> > On 09/07, Gregory Price wrote:
> > >
> > > On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> > > > --- a/kernel/hung_task.c
> > > > +++ b/kernel/hung_task.c
> > > > @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > > >  		return;
> > > >
> > > >  	this_round_count = 0;
> > > > -	rcu_read_lock();
> > > > -	for_each_process_thread(g, t) {
> > > > +	for_each_process_thread_rculock(g, t) {
> > > >  		if (!max_count--)
> > > > -			goto unlock;
> > > > +			goto out;
> > > ... snip ...
> > > > - unlock:
> > > > -	rcu_read_unlock();
> > > > -
> > > > +out:
> > > >  	if (!this_round_count)
> > > >  		return;
> > > >
> > >
> > > The sunken rcu_read_lock()/unlock() + scoped_guard usage makes this goto
> > > at a minimum very confusing, if not actually broken.
> >
> > I am afraid I misunderstood you concerns...
> >
>
> This might be my - admittedly shallow - understanding of scoped_guard,
> but does scoped guard handle goto correctly?

Yes, it does,

> and why it's generally discouraged to mix cleanup.h and goto.

Hmm, why? I didn't know...

Oleg.