linux-ext4 - [PATCH 3/3] mm/migrate: avoid atomic context on buffer_migrate_folio

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Message-ID: <20250330064732.3781046-4-mcgrof@kernel.org>
Date: Sat, 29 Mar 2025 23:47:32 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: brauner@...nel.org,
	jack@...e.cz,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org,
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Cc: willy@...radead.org,
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Subject: [PATCH 3/3] mm/migrate: avoid atomic context on buffer_migrate_folio_norefs() migration

The buffer_migrate_folio_norefs() should avoid holding the spin lock
held in order to ensure we can support large folios. The prior commit
"fs/buffer: avoid races with folio migrations on __find_get_block_slow()"
ripped out the only rationale for having the atomic context,  so we can
remove the spin lock call now.

Reported-by: kernel test robot <oliver.sang@...el.com>
Reported-by: syzbot+f3c6fda1297c748a7076@...kaller.appspotmail.com
Closes: https://lore.kernel.org/oe-lkp/202503101536.27099c77-lkp@intel.com
Fixes: 3c20917120ce ("block/bdev: enable large folio support for large logical block sizes")
Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
 mm/migrate.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 712ddd11f3f0..f3047c685706 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -861,12 +861,12 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 			}
 			bh = bh->b_this_page;
 		} while (bh != head);
+		spin_unlock(&mapping->i_private_lock);
 		if (busy) {
 			if (invalidated) {
 				rc = -EAGAIN;
 				goto unlock_buffers;
 			}
-			spin_unlock(&mapping->i_private_lock);
 			invalidate_bh_lrus();
 			invalidated = true;
 			goto recheck_buffers;
@@ -884,8 +884,6 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 	} while (bh != head);
 
 unlock_buffers:
-	if (check_refs)
-		spin_unlock(&mapping->i_private_lock);
 	bh = head;
 	do {
 		unlock_buffer(bh);
-- 
2.47.2