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Date:   Wed,  7 Dec 2022 12:27:15 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ted Tso <tytso@....edu>
Cc:     <linux-ext4@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>
Subject: [PATCH v4 12/13] ext4: Stop providing .writepage hook

Now we don't need .writepage hook for anything anymore. Reclaim is fine
with relying on .writepages to clean pages and we often couldn't do much
from the .writepage callback anyway. We only need to provide
.migrate_folio callback for the ext4_journalled_aops - let's use
buffer_migrate_page_norefs() there so that buffers cannot be modified
under jdb2's hands as that can cause data corruption. For example when
commit code does writeout of transaction buffers in
jbd2_journal_write_metadata_buffer(), we don't hold page lock or have
page writeback bit set or have the buffer locked. So page migration code
would go and happily migrate the page elsewhere while the copy is
running thus corrupting data.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/inode.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f3b3792c1c96..acf9d23c1cfb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3718,7 +3718,6 @@ static int ext4_iomap_swap_activate(struct swap_info_struct *sis,
 static const struct address_space_operations ext4_aops = {
 	.read_folio		= ext4_read_folio,
 	.readahead		= ext4_readahead,
-	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_write_begin,
 	.write_end		= ext4_write_end,
@@ -3736,7 +3735,6 @@ static const struct address_space_operations ext4_aops = {
 static const struct address_space_operations ext4_journalled_aops = {
 	.read_folio		= ext4_read_folio,
 	.readahead		= ext4_readahead,
-	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_write_begin,
 	.write_end		= ext4_journalled_write_end,
@@ -3745,6 +3743,7 @@ static const struct address_space_operations ext4_journalled_aops = {
 	.invalidate_folio	= ext4_journalled_invalidate_folio,
 	.release_folio		= ext4_release_folio,
 	.direct_IO		= noop_direct_IO,
+	.migrate_folio		= buffer_migrate_folio_norefs,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
 	.swap_activate		= ext4_iomap_swap_activate,
@@ -3753,7 +3752,6 @@ static const struct address_space_operations ext4_journalled_aops = {
 static const struct address_space_operations ext4_da_aops = {
 	.read_folio		= ext4_read_folio,
 	.readahead		= ext4_readahead,
-	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_da_write_begin,
 	.write_end		= ext4_da_write_end,
-- 
2.35.3

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