Re: [sos-linux-ext-patches] [PATCH RFC 09/11] mm/migrate: thread migration policy through a control struct

[Garg, Shivank]

On Wed, 2026-09-02 at 10:52 +0000, Shivank Garg wrote:
> Migration mode and reason describe one migration invocation, but are passed
> 

[...]

> @@ -2189,27 +2188,29 @@ static int migrate_folios_batch(struct list_head *from,
>   */
>  static int __migrate_lru_folios(struct list_head *from, new_folio_t get_new_folio,
>  		free_folio_t put_new_folio, unsigned long private,
> -		enum migrate_mode mode, enum migrate_reason reason,
> -		struct list_head *ret_folios,
> +		const struct migrate_control *ctl, struct list_head *ret_folios,
>  		struct migrate_pages_stats *stats)
>  {
>  	int rc, nr_failed = 0;
>  	LIST_HEAD(folios);
>  	LIST_HEAD(split_folios);
>  	struct migrate_pages_stats astats;
> +	struct migrate_control async_ctl;
>  
> -	if (mode == MIGRATE_ASYNC) {
> +	if (ctl->mode == MIGRATE_ASYNC) {
>  		rc = migrate_folios_batch(from, get_new_folio, put_new_folio,
> -				private, mode, reason, ret_folios,
> +				private, ctl, ret_folios,
>  				&split_folios, stats,
>  				NR_MAX_MIGRATE_PAGES_RETRY);
>  		goto out;
>  	}
>  
> +	async_ctl = *ctl;
> +	async_ctl.mode = MIGRATE_ASYNC;
>  	memset(&astats, 0, sizeof(astats));
>  	/* Try to migrate in batch with MIGRATE_ASYNC mode firstly */



Sashiko:
Can this lead to an uninitialized stack variable being used?
If __migrate_lru_folios() is called with ctl->mode == MIGRATE_ASYNC, the
early check jumps directly to the out label, bypassing the initialization
of async_ctl. If large folios were split during that first pass, the
!list_empty(&split_folios) check will be true.
Could this cause migrate_folios_batch() to execute with garbage policy? For
example, it might interpret the uninitialized async_ctl.mode as MIGRATE_SYNC,
causing unintended blocking and sleeping during what should be an asynchronous
migration.
--

Yes, this is valid issue. I should initialize async_ctl early before it make
goto jump.

---
 mm/migrate.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 731836664a86..c75300e00388 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2199,8 +2199,9 @@ static int __migrate_lru_folios(struct list_head *from, new_folio_t get_new_foli
 	LIST_HEAD(folios);
 	LIST_HEAD(split_folios);
 	struct migrate_pages_stats astats;
-	struct migrate_control async_ctl;
+	struct migrate_control async_ctl = *ctl;
 
+	async_ctl.mode = MIGRATE_ASYNC;
 	if (ctl->mode == MIGRATE_ASYNC) {
 		rc = migrate_folios_batch(from, get_new_folio, put_new_folio,
 				private, ctl, ret_folios,
@@ -2209,8 +2210,6 @@ static int __migrate_lru_folios(struct list_head *from, new_folio_t get_new_foli
 		goto out;
 	}
 
-	async_ctl = *ctl;
-	async_ctl.mode = MIGRATE_ASYNC;
 	memset(&astats, 0, sizeof(astats));
 	/* Try to migrate in batch with MIGRATE_ASYNC mode firstly */
 	rc = migrate_folios_batch(from, get_new_folio, put_new_folio, private,
-- 
2.43.0