linux-kernel - Re: [syzbot] [mm?] INFO: task hung in __rmap_walk

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Message-ID: <aV_BoaOogKt3fGGI@casper.infradead.org>
Date: Thu, 8 Jan 2026 14:39:29 +0000
From: Matthew Wilcox <willy@...radead.org>
To: syzbot <syzbot+2d9c96466c978346b55f@...kaller.appspotmail.com>
Cc: Liam.Howlett@...cle.com, akpm@...ux-foundation.org, david@...hat.com,
	harry.yoo@...cle.com, jannh@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com, riel@...riel.com,
	syzkaller-bugs@...glegroups.com, vbabka@...e.cz
Subject: Re: [syzbot] [mm?] INFO: task hung in __rmap_walk_file

On Fri, Oct 10, 2025 at 01:49:30PM -0700, syzbot wrote:
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133e89e2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17f3ba7c580000

#syz test

diff --git a/mm/migrate.c b/mm/migrate.c
index 5169f9717f60..4688b9e38cd2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1458,6 +1458,7 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio,
 	int page_was_mapped = 0;
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
+	enum ttu_flags ttu = 0;
 
 	if (folio_ref_count(src) == 1) {
 		/* page was freed from under us. So we are done. */
@@ -1498,8 +1499,6 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio,
 		goto put_anon;
 
 	if (folio_mapped(src)) {
-		enum ttu_flags ttu = 0;
-
 		if (!folio_test_anon(src)) {
 			/*
 			 * In shared mappings, try_to_unmap could potentially
@@ -1516,16 +1515,17 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio,
 
 		try_to_migrate(src, ttu);
 		page_was_mapped = 1;
-
-		if (ttu & TTU_RMAP_LOCKED)
-			i_mmap_unlock_write(mapping);
 	}
 
 	if (!folio_mapped(src))
 		rc = move_to_new_folio(dst, src, mode);
 
 	if (page_was_mapped)
-		remove_migration_ptes(src, !rc ? dst : src, 0);
+		remove_migration_ptes(src, !rc ? dst : src,
+				ttu ? RMP_LOCKED : 0);
+
+	if (ttu & TTU_RMAP_LOCKED)
+		i_mmap_unlock_write(mapping);
 
 unlock_put_anon:
 	folio_unlock(dst);