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Date:   Fri, 15 Nov 2019 11:22:10 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ted Tso <tytso@....edu>
Cc:     <linux-ext4@...r.kernel.org>, Eric Biggers <ebiggers@...nel.org>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH] jbd2: Make jbd2_handle_buffer_credits() handle reserved handles

The helper jbd2_handle_buffer_credits() doesn't correctly handle reserved
handles which can lead to crashes. Fix it getting of journal pointer to
work for reserved handles as well.

Fixes: a9a8344ee171 ("ext4, jbd2: Provide accessor function for handle credits")
Reported-by: Eric Biggers <ebiggers@...nel.org>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 include/linux/jbd2.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 3115eeb44039..a23a3528e07a 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1648,10 +1648,14 @@ static inline tid_t  jbd2_get_latest_transaction(journal_t *journal)
 	return tid;
 }
 
-
 static inline int jbd2_handle_buffer_credits(handle_t *handle)
 {
-	journal_t *journal = handle->h_transaction->t_journal;
+	journal_t *journal;
+
+	if (!handle->h_reserved)
+		journal = handle->h_transaction->t_journal;
+	else
+		journal = handle->h_journal;
 
 	return handle->h_total_credits -
 		DIV_ROUND_UP(handle->h_revoke_credits_requested,
-- 
2.16.4

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