From: Zhang Yi yi.zhang@huawei.com
[ Upstream commit 3c652c3a71de1d30d72dc82c3bead8deb48eb749 ]
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") Cc: stable@kernel.org Suggested-by: Jan Kara jack@suse.cz Signed-off-by: Zhang Yi yi.zhang@huawei.com Reviewed-by: Jan Kara jack@suse.cz Message-ID: 20250916093337.3161016-2-yi.zhang@huaweicloud.com Signed-off-by: Theodore Ts'o tytso@mit.edu [ Adjust context ] Signed-off-by: Sasha Levin sashal@kernel.org --- 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 72e9297d6adcb..97ff68f90d573 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -1550,6 +1550,7 @@ 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; @@ -1675,18 +1676,22 @@ 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); }
jbd_unlock_bh_state(bh); __brelse(bh); + if (wait_for_writeback) + wait_on_buffer(bh); drop: if (drop_reserve) { /* no need to reserve log space for this block -bzzz */