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@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Acked-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
> 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