[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 2/8] mm/oom_kill: convert process/thread iterators to for_each_*_rcu

[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_rcu()
and 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>
---
 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..8dd025965810 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_rcu(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_rcu(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_rcu(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_rcu(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_rcu(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

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

[Michal Hocko]

On Fri 04-09-26 16:29:54, 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_rcu()
> and 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>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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..8dd025965810 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_rcu(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_rcu(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_rcu(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_rcu(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_rcu(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

-- 
Michal Hocko
SUSE Labs

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

[SJ Park]

On Fri,  4 Sep 2026 16:29:54 +0800 Ye Liu <ye.liu@linux.dev> 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_rcu()
> and for_each_thread_rcu(), so that the RCU read-side critical section
> is scoped to the loop body.

Looks clean to me :)

> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

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


Thanks,
SJ

[...]

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

[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_rcu().

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 mm/ksm.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 49d48d1e0998..fa5e4c47fb1b 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_rcu(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

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

[Michal Hocko]

On Fri 04-09-26 16:29:55, 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_rcu().
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/ksm.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 49d48d1e0998..fa5e4c47fb1b 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_rcu(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
> 

-- 
Michal Hocko
SUSE Labs

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

[SJ Park]

On Fri,  4 Sep 2026 16:29:55 +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 mm/ksm.c with for_each_process_rcu().
> 
> No functional change.

Looks clean to me, thank you.

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

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


Thanks,
SJ

[...]

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

[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_rcu().

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 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..63a2ff08ee33 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_rcu(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_rcu(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_rcu(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_rcu(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

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

[Michal Hocko]

On Fri 04-09-26 16:29:56, 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_rcu().
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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..63a2ff08ee33 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_rcu(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_rcu(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_rcu(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_rcu(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
> 

-- 
Michal Hocko
SUSE Labs

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

[SJ Park]

On Fri,  4 Sep 2026 16:29:56 +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_rcu().
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> ---
>  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..63a2ff08ee33 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_rcu(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_rcu(tsk) {
>  		struct task_struct *t = task_early_kill(tsk, force_early);
>  		unsigned long addr;

This moves pgoff assignment out of the RCU critical section.  Is this fine and
making no real functional change?  If it is fine and no functiona change, could
we clarify the reasons on the commit message?


Thanks,
SJ

[...]

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

[Miaohe Lin]

On 2026/9/4 16:29, 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_rcu().
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

With SJ's comment addressed:

Acked-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks.
.

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

[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_*_rcu() macros.

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 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 +--
 9 files changed, 11 insertions(+), 30 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b3c8553d7bd6..bc70fd21561a 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_rcu(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..a27b2382fda9 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_rcu(p, t) {
 		__thaw_task(t);
 	}
-	rcu_read_unlock();
 }
 
 /**
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 6fcc94ce4ca9..76871f78497f 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -315,8 +315,7 @@ 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_rcu(g, t) {
 		if (!max_count--)
 			goto unlock;
 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
@@ -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();
-
+unlock:
 	if (!this_round_count)
 		return;
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c56a7f91d72e..9c3dce0f0c4b 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_rcu(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..c48a84a0da82 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_rcu(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..a41cdd2ff02f 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_rcu(g, p)
 		uclamp_update_util_min_rt_default(p);
 }
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 72236db67983..8f37b1a7adfe 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_rcu(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..e522433ec8a5 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_rcu(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..61fe2d4727ce 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_rcu(g, t) {
 		atomic_long_andnot(BIT(bit),
 				   &t->unwind_info.unwind_mask);
 		if (t->unwind_info.cache)
-- 
2.25.1

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Mixing goto-based error cleanup with guard() scopes in the same function (`alloc_retstack_tasklist`).
--

commit f2b0046bb431ebefb3d059e22788f2810f0e6684
Author: Ye Liu <liuye@kylinos.cn>
kernel: convert process/thread iterators to for_each_*_rcu

This commit converts multiple manual rcu_read_lock() and iterator blocks
across the kernel to use the new for_each_*_rcu() macros.

> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 40d373d65f9b9..e522433ec8a5a 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_rcu(g, t) {
>  		if (start == end) {
>  			ret = -EAGAIN;
> -			goto unlock;
> +			goto free;

[Severity: Low]
Does this change violate the cleanup subsystem guidelines by mixing paradigms?

The for_each_process_thread_rcu() macro expands to include a
scoped_guard(rcu). However, alloc_retstack_tasklist() still uses a goto free
statement to manually clean up the ret_stack_list array allocations upon error.

According to the kernel guidelines in include/linux/cleanup.h, the
expectation is that a given function either converts all resources requiring
a goto cleanup to scope-based cleanup, or converts none of them. Mixing
goto-based error handling with guard() or scoped_guard() scopes in the same
function should be avoided.

>  		}
>  
>  		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]);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260904083001.553587-1-ye.liu@linux.dev?part=5

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

[Michal Hocko]

On Fri 04-09-26 16:29:57, 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_*_rcu() macros.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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 +--
>  9 files changed, 11 insertions(+), 30 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index b3c8553d7bd6..bc70fd21561a 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_rcu(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..a27b2382fda9 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_rcu(p, t) {
>  		__thaw_task(t);
>  	}
> -	rcu_read_unlock();
>  }
>  
>  /**
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 6fcc94ce4ca9..76871f78497f 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -315,8 +315,7 @@ 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_rcu(g, t) {
>  		if (!max_count--)
>  			goto unlock;
>  		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
> @@ -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();
> -
> +unlock:
>  	if (!this_round_count)
>  		return;
>  
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c56a7f91d72e..9c3dce0f0c4b 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_rcu(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..c48a84a0da82 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_rcu(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..a41cdd2ff02f 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_rcu(g, p)
>  		uclamp_update_util_min_rt_default(p);
>  }
>  
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 72236db67983..8f37b1a7adfe 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_rcu(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..e522433ec8a5 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_rcu(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..61fe2d4727ce 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_rcu(g, t) {
>  		atomic_long_andnot(BIT(bit),
>  				   &t->unwind_info.unwind_mask);
>  		if (t->unwind_info.cache)
> -- 
> 2.25.1
> 

-- 
Michal Hocko
SUSE Labs

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

[Günther Noack]

On Fri, Sep 04, 2026 at 04:29:57PM +0800, Ye Liu wrote:
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 6fcc94ce4ca9..76871f78497f 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -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();
> -
> +unlock:
>  	if (!this_round_count)
>  		return;

The label name "unlock" is misleading now.  There is no further unlock
happening after it any more.

–Günther

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

[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_*_rcu() macros.

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 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..da36ba73dc17 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_rcu(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..3f96d21b84ab 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_rcu(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_rcu(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

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

[Oleg Nesterov]

On 09/04, Ye Liu wrote:
>
> @@ -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_rcu(p) {
>  			if (same_thread_group(task, p))
>  				continue;

Hmm... I am not aware of for_each_process_rcu(), but looking at this
change I guess it includes something like scope_guard(rcu) ?

Perhaps makes sense, but the naming looks sligthly confusing to me.
I mean, to for_each_process_rcu() looks like (say) list_for_each_entry_rcu()
where _rcu has another meaning...

Oleg.

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

[Lorenzo Stoakes (ARM)]

Please cc everybody on every patch in the series :) it makes it incredible hard
for me to see context otherwise.

I can already see a comment I'd like to leave on another patch in the series but
it's a total pain for me go retrieve that to do it.

And I worry about acking one bit only to find out a horrible flaw in another
part :P

Can you please make sure to do that on any respin?...

On Fri, Sep 04, 2026 at 04:29:58PM +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_*_rcu() macros.

Probably worth mentioning that they hold the RCU lock in a scoped guard over the
operation.

>
> No functional change.
>
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

In general it looks reasonable to me, but I wonder if you're correctly including
linux/cleanup.h to have the scope guard available...

Anyway can check that on respin with the right cc ;)

> ---
>  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..da36ba73dc17 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)

Side-note - I wonder if this really belongs in mm/oom_kill.c? Seems really odd
to have it here.

>  	if (mm) {
>  		struct task_struct *p;
>
> -		rcu_read_lock();
> -		for_each_process(p) {
> +		for_each_process_rcu(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..3f96d21b84ab 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_rcu(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_rcu(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 6/8] fs: convert process/thread iterators to for_each_*_rcu

[Michal Hocko]

On Fri 04-09-26 16:29:58, 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_*_rcu() macros.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@kylinos.cn>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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..da36ba73dc17 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_rcu(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..3f96d21b84ab 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_rcu(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_rcu(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
> 

-- 
Michal Hocko
SUSE Labs

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

[Alexey Dobriyan]

On Fri, Sep 04, 2026 at 04:29:58PM +0800, Ye Liu wrote:
> --- 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_rcu(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:

What's going on here?
Now it's RCU unlock after mmdrop().

These scoped guards kind of suck unless you allow infinite line length.

	A

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

[Lorenzo Stoakes (ARM)]

On Tue, Sep 08, 2026 at 07:45:15PM +0300, Alexey Dobriyan wrote:
> On Fri, Sep 04, 2026 at 04:29:58PM +0800, Ye Liu wrote:
> > --- 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_rcu(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:
>
> What's going on here?
> Now it's RCU unlock after mmdrop().

No it's not, scoped_guard() is scoped to the for_each_process_rcu() block which
ends before mmdrop(), i.e. the exact same scope as before.

That closing '}' is attached to the if (mm).

>
> These scoped guards kind of suck unless you allow infinite line length.
>
> 	A

--
Cheers, Lorenzo

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

[Alexey Dobriyan]

On Tue, Sep 08, 2026 at 06:10:17PM +0100, Lorenzo Stoakes (ARM) wrote:
> On Tue, Sep 08, 2026 at 07:45:15PM +0300, Alexey Dobriyan wrote:
> > On Fri, Sep 04, 2026 at 04:29:58PM +0800, Ye Liu wrote:
> > > --- 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_rcu(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:
> >
> > What's going on here?
> > Now it's RCU unlock after mmdrop().
> 
> No it's not, scoped_guard() is scoped to the for_each_process_rcu() block which
> ends before mmdrop(), i.e. the exact same scope as before.
> 
> That closing '}' is attached to the if (mm).

OK.

I think naming (and macro) are misguided:
* _rcu means "use under RCU section opened elsewhere",
  this one is "I open and close RCU section myself".

* not every 2 lines should be combined into new interface.

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

[Lorenzo Stoakes (ARM)]

On Tue, Sep 08, 2026 at 08:26:54PM +0300, Alexey Dobriyan wrote:
> On Tue, Sep 08, 2026 at 06:10:17PM +0100, Lorenzo Stoakes (ARM) wrote:
> > On Tue, Sep 08, 2026 at 07:45:15PM +0300, Alexey Dobriyan wrote:
> > > On Fri, Sep 04, 2026 at 04:29:58PM +0800, Ye Liu wrote:
> > > > --- 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_rcu(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:
> > >
> > > What's going on here?
> > > Now it's RCU unlock after mmdrop().
> >
> > No it's not, scoped_guard() is scoped to the for_each_process_rcu() block which
> > ends before mmdrop(), i.e. the exact same scope as before.
> >
> > That closing '}' is attached to the if (mm).
>
> OK.
>
> I think naming (and macro) are misguided:
> * _rcu means "use under RCU section opened elsewhere",
>   this one is "I open and close RCU section myself".

You're replying to a v1 of a series that has a v2 which changes the naming.

>
> * not every 2 lines should be combined into new interface.

Nobody is suggesting every 2 lines should be combined into a new interface.

They're suggesting that explicitly tying lock lifetime to block scope is a
really good idea.

And having debugged lots of locking issues, I agree.

Anyway the v2 is at:

https://lore.kernel.org/all/20260907081334.1152889-1-ye.liu@linux.dev/


--
Cheers, Lorenzo

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

[Oleg Nesterov]

On 09/08, Alexey Dobriyan wrote:
>
> On Fri, Sep 04, 2026 at 04:29:58PM +0800, Ye Liu wrote:
> > --- 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_rcu(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:
>
> What's going on here?
> Now it's RCU unlock after mmdrop().

Confused... Why do you think so?

I think mmdrop() is called after rcu_read_unlock(), with or without this change.

No?

Oleg.

[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