[PATCH v2 1/1] jbd2: gracefully abort on checkpointing state corruptions

[Milos Nikic <nikic.milos@gmail.com>]

This patch targets two internal state machine invariants in checkpoint.c
residing inside functions that natively return integer error codes.

- In jbd2_cleanup_journal_tail(): A blocknr of 0 indicates a severely
corrupted journal superblock. Replaced the J_ASSERT with a WARN_ON_ONCE
and a graceful journal abort, returning -EFSCORRUPTED.

- In jbd2_log_do_checkpoint(): Replaced the J_ASSERT_BH checking for
an unexpected buffer_jwrite state. If the warning triggers, we
explicitly drop the just-taken get_bh() reference and call __flush_batch()
to safely clean up any previously queued buffers in the j_chkpt_bhs array,
preventing a memory leak before returning -EFSCORRUPTED.

Signed-off-by: Milos Nikic <nikic.milos@gmail.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
---
 Changes in v2:

    Replaced the -EUCLEAN error code with -EFSCORRUPTED to better align with ext4/jbd2 semantics for on-disk metadata inconsistencies (per Baokun's review).

    Reordered the error path in jbd2_log_do_checkpoint() so that jbd2_journal_abort() is called after __flush_batch(). This ensures cleanly batched buffers are logically flushed before the journal kill switch is flipped.

    Collected Reviewed-by tags from Andreas Dilger, Zhang Yi, and Baokun Li.

Changes in v1:

    Initial implementation converting J_ASSERTs in jbd2_cleanup_journal_tail() and jbd2_log_do_checkpoint() to WARN_ON_ONCE and graceful journal aborts.

 fs/jbd2/checkpoint.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index de89c5bef607..1508e2f54462 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -267,7 +267,15 @@ int jbd2_log_do_checkpoint(journal_t *journal)
 			 */
 			BUFFER_TRACE(bh, "queue");
 			get_bh(bh);
-			J_ASSERT_BH(bh, !buffer_jwrite(bh));
+			if (WARN_ON_ONCE(buffer_jwrite(bh))) {
+				put_bh(bh); /* drop the ref we just took */
+				spin_unlock(&journal->j_list_lock);
+				/* Clean up any previously batched buffers */
+				if (batch_count)
+					__flush_batch(journal, &batch_count);
+				jbd2_journal_abort(journal, -EFSCORRUPTED);
+				return -EFSCORRUPTED;
+			}
 			journal->j_chkpt_bhs[batch_count++] = bh;
 			transaction->t_chp_stats.cs_written++;
 			transaction->t_checkpoint_list = jh->b_cpnext;
@@ -325,7 +333,10 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
 
 	if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
 		return 1;
-	J_ASSERT(blocknr != 0);
+	if (WARN_ON_ONCE(blocknr == 0)) {
+		jbd2_journal_abort(journal, -EFSCORRUPTED);
+		return -EFSCORRUPTED;
+	}
 
 	/*
 	 * We need to make sure that any blocks that were recently written out
-- 
2.53.0