From: Zhang Yi When releasing file system metadata blocks in jbd2_journal_forget(), if this buffer has not yet been checkpointed, it may have already been written back, currently be in the process of being written back, or has not yet written back. jbd2_journal_forget() calls jbd2_journal_try_remove_checkpoint() to check the buffer's status and add it to the current transaction if it has not been written back. This buffer can only be reallocated after the transaction is committed. jbd2_journal_try_remove_checkpoint() attempts to lock the buffer and check its dirty status while holding the buffer lock. If the buffer has already been written back, everything proceeds normally. However, there are two issues. First, the function returns immediately if the buffer is locked by the write-back process. It does not wait for the write-back to complete. Consequently, until the current transaction is committed and the block is reallocated, there is no guarantee that the I/O will complete. This means that ongoing I/O could write stale metadata to the newly allocated block, potentially corrupting data. Second, the function unlocks the buffer as soon as it detects that the buffer is still dirty. If a concurrent write-back occurs immediately after this unlocking and before clear_buffer_dirty() is called in jbd2_journal_forget(), data corruption can theoretically still occur. Although these two issues are unlikely to occur in practice since the undergoing metadata writeback I/O does not take this long to complete, it's better to explicitly ensure that all ongoing I/O operations are completed. Fixes: 597599268e3b ("jbd2: discard dirty data when forgetting an un-journalled buffer") Suggested-by: Jan Kara Signed-off-by: Zhang Yi --- fs/jbd2/transaction.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index c7867139af69..3e510564de6e 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -1659,6 +1659,7 @@ int jbd2_journal_forget(handle_t *handle, struct buffer_head *bh) int drop_reserve = 0; int err = 0; int was_modified = 0; + int wait_for_writeback = 0; if (is_handle_aborted(handle)) return -EROFS; @@ -1782,18 +1783,22 @@ int jbd2_journal_forget(handle_t *handle, struct buffer_head *bh) } /* - * The buffer is still not written to disk, we should - * attach this buffer to current transaction so that the - * buffer can be checkpointed only after the current - * transaction commits. + * The buffer has not yet been written to disk. We should + * either clear the buffer or ensure that the ongoing I/O + * is completed, and attach this buffer to current + * transaction so that the buffer can be checkpointed only + * after the current transaction commits. */ clear_buffer_dirty(bh); + wait_for_writeback = 1; __jbd2_journal_file_buffer(jh, transaction, BJ_Forget); spin_unlock(&journal->j_list_lock); } drop: __brelse(bh); spin_unlock(&jh->b_state_lock); + if (wait_for_writeback) + wait_on_buffer(bh); jbd2_journal_put_journal_head(jh); if (drop_reserve) { /* no need to reserve log space for this block -bzzz */ -- 2.46.1 From: Zhang Yi When freeing metadata blocks in nojournal mode, ext4_forget() calls bforget() to clear the dirty flag on the buffer_head and remvoe associated mappings. This is acceptable if the metadata has not yet begun to be written back. However, if the write-back has already started but is not yet completed, ext4_forget() will have no effect. Subsequently, ext4_mb_clear_bb() will immediately return the block to the mb allocator. This block can then be reallocated immediately, potentially causing an data corruption issue. Fix this by clearing the buffer's dirty flag and waiting for the ongoing I/O to complete, ensuring that no further writes to stale data will occur. Fixes: 16e08b14a455 ("ext4: cleanup clean_bdev_aliases() calls") Reported-by: Gao Xiang Closes: https://lore.kernel.org/linux-ext4/a9417096-9549-4441-9878-b1955b899b4e@huaweicloud.com/ Signed-off-by: Zhang Yi --- fs/ext4/ext4_jbd2.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c index b3e9b7bd7978..a0e66bc10093 100644 --- a/fs/ext4/ext4_jbd2.c +++ b/fs/ext4/ext4_jbd2.c @@ -280,9 +280,16 @@ int __ext4_forget(const char *where, unsigned int line, handle_t *handle, bh, is_metadata, inode->i_mode, test_opt(inode->i_sb, DATA_FLAGS)); - /* In the no journal case, we can just do a bforget and return */ + /* + * In the no journal case, we should wait for the ongoing buffer + * to complete and do a forget. + */ if (!ext4_handle_valid(handle)) { - bforget(bh); + if (bh) { + clear_buffer_dirty(bh); + wait_on_buffer(bh); + __bforget(bh); + } return 0; } -- 2.46.1