[PATCH 4.14] ext4: fix cgroup writeback accounting with fs-layer encryption

[PATCH 4.14] ext4: fix cgroup writeback accounting with fs-layer encryption

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

commit ffec85d53d0f39ee4680a2cf0795255e000e1feb upstream.

When writing a page from an encrypted file that is using
filesystem-layer encryption (not inline encryption), ext4 encrypts the
pagecache page into a bounce page, then writes the bounce page.

It also passes the bounce page to wbc_account_cgroup_owner().  That's
incorrect, because the bounce page is a newly allocated temporary page
that doesn't have the memory cgroup of the original pagecache page.
This makes wbc_account_cgroup_owner() not account the I/O to the owner
of the pagecache page as it should.

Fix this by always passing the pagecache page to
wbc_account_cgroup_owner().

Fixes: 001e4a8775f6 ("ext4: implement cgroup writeback support")
Cc: stable@vger.kernel.org
Reported-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230203005503.141557-1-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/page-io.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 3de933354a08b..bf910f2664690 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -388,7 +388,8 @@ static int io_submit_init_bio(struct ext4_io_submit *io,
 
 static int io_submit_add_bh(struct ext4_io_submit *io,
 			    struct inode *inode,
-			    struct page *page,
+			    struct page *pagecache_page,
+			    struct page *bounce_page,
 			    struct buffer_head *bh)
 {
 	int ret;
@@ -403,10 +404,11 @@ static int io_submit_add_bh(struct ext4_io_submit *io,
 			return ret;
 		io->io_bio->bi_write_hint = inode->i_write_hint;
 	}
-	ret = bio_add_page(io->io_bio, page, bh->b_size, bh_offset(bh));
+	ret = bio_add_page(io->io_bio, bounce_page ?: pagecache_page,
+			   bh->b_size, bh_offset(bh));
 	if (ret != bh->b_size)
 		goto submit_and_retry;
-	wbc_account_io(io->io_wbc, page, bh->b_size);
+	wbc_account_io(io->io_wbc, pagecache_page, bh->b_size);
 	io->io_next_block++;
 	return 0;
 }
@@ -514,8 +516,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 	do {
 		if (!buffer_async_write(bh))
 			continue;
-		ret = io_submit_add_bh(io, inode,
-				       data_page ? data_page : page, bh);
+		ret = io_submit_add_bh(io, inode, page, data_page, bh);
 		if (ret) {
 			/*
 			 * We only get here on ENOMEM.  Not much else
-- 
2.39.2