ext4: fix cgroup writeback accounting with fs-layer encryption

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>

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index beaec6d81074a7e21c5ea3123700bd8332859a58..1e4db96a04e630b9a118d34580fa5c23c2db14a6 100644 (file)
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -409,7 +409,8 @@ static void io_submit_init_bio(struct ext4_io_submit *io,
 
 static void 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;
@@ -421,10 +422,11 @@ submit_and_retry:
        }
        if (io->io_bio == NULL)
                io_submit_init_bio(io, bh);
-       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_cgroup_owner(io->io_wbc, page, bh->b_size);
+       wbc_account_cgroup_owner(io->io_wbc, pagecache_page, bh->b_size);
        io->io_next_block++;
 }
 
@@ -561,8 +563,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
        do {
                if (!buffer_async_write(bh))
                        continue;
-               io_submit_add_bh(io, inode,
-                                bounce_page ? bounce_page : page, bh);
+               io_submit_add_bh(io, inode, page, bounce_page, bh);
        } while ((bh = bh->b_this_page) != head);
 unlock:
        unlock_page(page);