[PATCH 3/4] ext4: fix a potential assertion failure due to improperly dirtied buffer

zhangshida
2024-08-30T05:37:54Z

On an old kernel version(4.19, ext3, data=journal, pagesize=64k),
an assertion failure will occasionally be triggered by the line below:
-----------
jbd2_journal_commit_transaction
{
...
J_ASSERT_BH(bh, !buffer_dirty(bh));
/*
* The buffer on BJ_Forget list and not jbddirty means
...
}
-----------

The same condition may also be applied to the lattest kernel version.

When blocksize < pagesize and we truncate a file, there can be buffers in
the mapping tail page beyond i_size. These buffers will be filed to
transaction's BJ_Forget list by ext4_journalled_invalidatepage() during
truncation. When the transaction doing truncate starts committing, we can
grow the file again. This calls __block_write_begin() which allocates new
blocks under these buffers in the tail page we go through the branch:

if (buffer_new(bh)) {
clean_bdev_bh_alias(bh);
if (folio_test_uptodate(folio)) {
clear_buffer_new(bh);
set_buffer_uptodate(bh);
mark_buffer_dirty(bh);
continue;
}
...
}

Hence buffers on BJ_Forget list of the committing transaction get marked
dirty and this triggers the jbd2 assertion.

Teach ext4_block_write_begin() to properly handle files with data
journalling by avoiding dirtying them directly. Instead of
folio_zero_new_buffers() we use ext4_journalled_zero_new_buffers() which
takes care of handling journalling. We also don't need to mark new uptodate
buffers as dirty in ext4_block_write_begin(). That will be either done
either by block_commit_write() in case of success or by
folio_zero_new_buffers() in case of failure.

Reported-by: Baolin Liu <liubaolin@kylinos.cn>
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
fs/ext4/ext4.h | 3 ++-
fs/ext4/inline.c | 7 ++++---
fs/ext4/inode.c | 42 ++++++++++++++++++++++++++++++++++--------
3 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 5f8257b68190..b653bd423b11 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3851,7 +3851,8 @@ static inline int ext4_buffer_uptodate(struct buffer_head *bh)
return buffer_uptodate(bh);
}

-extern int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
+extern int ext4_block_write_begin(handle_t *handle, struct folio *folio,
+ loff_t pos, unsigned len,
get_block_t *get_block);
#endif /* __KERNEL__ */

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 0a1a8431e281..8d5599d5af27 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -601,10 +601,11 @@ static int ext4_convert_inline_data_to_extent(struct address_space *mapping,
goto out;

if (ext4_should_dioread_nolock(inode)) {
- ret = ext4_block_write_begin(folio, from, to,
+ ret = ext4_block_write_begin(handle, folio, from, to,
ext4_get_block_unwritten);
} else
- ret = ext4_block_write_begin(folio, from, to, ext4_get_block);
+ ret = ext4_block_write_begin(handle, folio, from, to,
+ ext4_get_block);

if (!ret && ext4_should_journal_data(inode)) {
ret = ext4_walk_page_buffers(handle, inode,
@@ -856,7 +857,7 @@ static int ext4_da_convert_inline_data_to_extent(struct address_space *mapping,
goto out;
}

- ret = ext4_block_write_begin(folio, 0, inline_size,
+ ret = ext4_block_write_begin(NULL, folio, 0, inline_size,
ext4_da_get_block_prep);
if (ret) {
up_read(&EXT4_I(inode)->xattr_sem);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4964c67e029e..a28f279fd02f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -49,6 +49,11 @@

#include <trace/events/ext4.h>

+static void ext4_journalled_zero_new_buffers(handle_t *handle,
+ struct inode *inode,
+ struct folio *folio,
+ unsigned from, unsigned to);
+
static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
struct ext4_inode_info *ei)
{
@@ -1041,7 +1046,8 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
return ret;
}

-int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
+int ext4_block_write_begin(handle_t *handle, struct folio *folio,
+ loff_t pos, unsigned len,
get_block_t *get_block)
{
unsigned from = pos & (PAGE_SIZE - 1);
@@ -1055,6 +1061,7 @@ int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
struct buffer_head *bh, *head, *wait[2];
int nr_wait = 0;
int i;
+ bool should_journal_data = ext4_should_journal_data(inode);

BUG_ON(!folio_test_locked(folio));
BUG_ON(from > PAGE_SIZE);
@@ -1084,10 +1091,22 @@ int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
if (err)
break;
if (buffer_new(bh)) {
+ /*
+ * We may be zeroing partial buffers or all new
+ * buffers in case of failure. Prepare JBD2 for
+ * that.
+ */
+ if (should_journal_data)
+ do_journal_get_write_access(handle,
+ inode, bh);
if (folio_test_uptodate(folio)) {
- clear_buffer_new(bh);
+ /*
+ * Unlike __block_write_begin() we leave
+ * dirtying of new uptodate buffers to
+ * ->write_end() time or
+ * folio_zero_new_buffers().
+ */
set_buffer_uptodate(bh);
- mark_buffer_dirty(bh);
continue;
}
if (block_end > to || block_start < from)
@@ -1117,7 +1136,11 @@ int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
err = -EIO;
}
if (unlikely(err)) {
- folio_zero_new_buffers(folio, from, to);
+ if (should_journal_data)
+ ext4_journalled_zero_new_buffers(handle, inode, folio,
+ from, to);
+ else
+ folio_zero_new_buffers(folio, from, to);
} else if (fscrypt_inode_uses_fs_layer_crypto(inode)) {
for (i = 0; i < nr_wait; i++) {
int err2;
@@ -1215,10 +1238,11 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
folio_wait_stable(folio);

if (ext4_should_dioread_nolock(inode))
- ret = ext4_block_write_begin(folio, pos, len,
+ ret = ext4_block_write_begin(handle, folio, pos, len,
ext4_get_block_unwritten);
else
- ret = ext4_block_write_begin(folio, pos, len, ext4_get_block);
+ ret = ext4_block_write_begin(handle, folio, pos, len,
+ ext4_get_block);
if (!ret && ext4_should_journal_data(inode)) {
ret = ext4_walk_page_buffers(handle, inode,
folio_buffers(folio), from, to,
@@ -2951,7 +2975,8 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
if (IS_ERR(folio))
return PTR_ERR(folio);

- ret = ext4_block_write_begin(folio, pos, len, ext4_da_get_block_prep);
+ ret = ext4_block_write_begin(NULL, folio, pos, len,
+ ext4_da_get_block_prep);
if (ret < 0) {
folio_unlock(folio);
folio_put(folio);
@@ -6205,7 +6230,8 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
if (folio_pos(folio) + len > size)
len = size - folio_pos(folio);

- err = __block_write_begin(&folio->page, 0, len, ext4_get_block);
+ err = ext4_block_write_begin(handle, folio, 0, len,
+ ext4_get_block);
if (!err) {
ret = VM_FAULT_SIGBUS;
if (ext4_journal_folio_buffers(handle, folio, len))
--
2.33.0