bcachefs: Dump journal state when we get stuck

We had a bug reported where the journal is failing to allocate a journal
write - this should help figure out what's going on.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/journal_io.c

@@ -1383,6 +1383,7 @@ void bch2_journal_write(struct closure *cl)
 	struct jset_entry *start, *end;
 	struct jset *jset;
 	struct bio *bio;
+	char *journal_debug_buf = NULL;
 	bool validate_before_checksum = false;
 	unsigned i, sectors, bytes, u64s, nr_rw_members = 0;
 	int ret;
@@ -1484,6 +1485,12 @@ void bch2_journal_write(struct closure *cl)
 		goto retry_alloc;
 	}
 
+	if (ret) {
+		journal_debug_buf = kmalloc(4096, GFP_ATOMIC);
+		if (journal_debug_buf)
+			__bch2_journal_debug_to_text(&_PBUF(journal_debug_buf, 4096), j);
+	}
+
 	/*
 	 * write is allocated, no longer need to account for it in
 	 * bch2_journal_space_available():
@@ -1498,7 +1505,9 @@ void bch2_journal_write(struct closure *cl)
 	spin_unlock(&j->lock);
 
 	if (ret) {
-		bch_err(c, "Unable to allocate journal write");
+		bch_err(c, "Unable to allocate journal write:\n%s",
+			journal_debug_buf);
+		kfree(journal_debug_buf);
 		bch2_fatal_error(c);
 		continue_at(cl, journal_write_done, system_highpri_wq);
 		return;