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ext4: fix a potential assertion failure due to improperly dirtied buffer 

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>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240830053739.3588573-4-zhangshida@kylinos.cn
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Shida Zhang 2024-08-30 13:37:38 +08:00 committed by Theodore Ts'o
parent 6b730a4050
commit cb3de5fc87
3 changed files with 40 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/ext4/ext4.h
View File

@ -3853,7 +3853,8 @@ 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__ */

7
fs/ext4/inline.c
View File

@ -601,10 +601,11 @@ retry:
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);

42
fs/ext4/inode.c
View File

@ -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)
{
@ -1023,7 +1028,8 @@ 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);
@ -1037,6 +1043,7 @@ 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);
@ -1066,10 +1073,22 @@ 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)
@ -1099,7 +1118,11 @@ 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;
@ -1197,10 +1220,11 @@ retry_journal:
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,
@ -2926,7 +2950,8 @@ retry:
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);
@ -6183,7 +6208,8 @@ retry_alloc:
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))