In commit code, we scan buffers attached to a transaction. During this
scan, we sometimes have to drop j_list_lock and then we recheck whether
the journal buffer head didn't get freed by journal_try_to_free_buffers().
But checking for buffer_jbd(bh) isn't enough because a new journal head
could get attached to our buffer head. So add a check whether the journal
head remained the same and whether it's still at the same transaction and
list.
This is a nasty bug and can cause problems like memory corruption (use after
free) or trigger various assertions in JBD code (observed).
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/jbd/commit.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
Andrew, would you please merge it? Thanks. BTW, JBD2 does not have the problem
since we handle ordered mode data buffers differently there.
diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 06560c5..618e21c 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -241,7 +241,7 @@ write_out_data:
spin_lock(&journal->j_list_lock);
}
/* Someone already cleaned up the buffer? */
- if (!buffer_jbd(bh)
+ if (!buffer_jbd(bh) || bh2jh(bh) != jh
|| jh->b_transaction != commit_transaction
|| jh->b_jlist != BJ_SyncData) {
jbd_unlock_bh_state(bh);
@@ -478,7 +478,9 @@ void journal_commit_transaction(journal_t *journal)
spin_lock(&journal->j_list_lock);
continue;
}
- if (buffer_jbd(bh) && jh->b_jlist == BJ_Locked) {
+ if (buffer_jbd(bh) && bh2jh(bh) == jh &&
+ jh->b_transaction == commit_transaction &&
+ jh->b_jlist == BJ_Locked) {
__journal_unfile_buffer(jh);
jbd_unlock_bh_state(bh);
journal_remove_journal_head(bh);
--
1.6.0.2
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