jbd: Fix oops in journal_remove_journal_head()
journal_remove_journal_head() can oops when trying to access journal_head
returned by bh2jh(). This is caused for example by the following race:
TASK1 TASK2
journal_commit_transaction()
...
processing t_forget list
__journal_refile_buffer(jh);
if (!jh->b_transaction) {
jbd_unlock_bh_state(bh);
journal_try_to_free_buffers()
journal_grab_journal_head(bh)
jbd_lock_bh_state(bh)
__journal_try_to_free_buffer()
journal_put_journal_head(jh)
journal_remove_journal_head(bh);
journal_put_journal_head() in TASK2 sees that b_jcount == 0 and buffer is not
part of any transaction and thus frees journal_head before TASK1 gets to doing
so. Note that even buffer_head can be released by try_to_free_buffers() after
journal_put_journal_head() which adds even larger opportunity for oops (but I
didn't see this happen in reality).
Fix the problem by making transactions hold their own journal_head reference
(in b_jcount). That way we don't have to remove journal_head explicitely via
journal_remove_journal_head() and instead just remove journal_head when
b_jcount drops to zero. The result of this is that [__]journal_refile_buffer(),
[__]journal_unfile_buffer(), and __journal_remove_checkpoint() can free
journal_head which needs modification of a few callers. Also we have to be
careful because once journal_head is removed, buffer_head might be freed as
well. So we have to get our own buffer_head reference where it matters.
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index eedd201..8799207 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -258,10 +258,6 @@
jbd_unlock_bh_state(bh);
if (locked)
unlock_buffer(bh);
- journal_remove_journal_head(bh);
- /* One for our safety reference, other for
- * journal_remove_journal_head() */
- put_bh(bh);
release_data_buffer(bh);
}
@@ -455,14 +451,9 @@
}
if (buffer_jbd(bh) && bh2jh(bh) == jh &&
jh->b_transaction == commit_transaction &&
- jh->b_jlist == BJ_Locked) {
+ jh->b_jlist == BJ_Locked)
__journal_unfile_buffer(jh);
- jbd_unlock_bh_state(bh);
- journal_remove_journal_head(bh);
- put_bh(bh);
- } else {
- jbd_unlock_bh_state(bh);
- }
+ jbd_unlock_bh_state(bh);
release_data_buffer(bh);
cond_resched_lock(&journal->j_list_lock);
}
@@ -807,10 +798,16 @@
while (commit_transaction->t_forget) {
transaction_t *cp_transaction;
struct buffer_head *bh;
+ int try_to_free = 0;
jh = commit_transaction->t_forget;
spin_unlock(&journal->j_list_lock);
bh = jh2bh(jh);
+ /*
+ * Get a reference so that bh cannot be freed before we are
+ * done with it.
+ */
+ get_bh(bh);
jbd_lock_bh_state(bh);
J_ASSERT_JH(jh, jh->b_transaction == commit_transaction ||
jh->b_transaction == journal->j_running_transaction);
@@ -868,28 +865,27 @@
__journal_insert_checkpoint(jh, commit_transaction);
if (is_journal_aborted(journal))
clear_buffer_jbddirty(bh);
- JBUFFER_TRACE(jh, "refile for checkpoint writeback");
- __journal_refile_buffer(jh);
- jbd_unlock_bh_state(bh);
} else {
J_ASSERT_BH(bh, !buffer_dirty(bh));
- /* The buffer on BJ_Forget list and not jbddirty means
+ /*
+ * The buffer on BJ_Forget list and not jbddirty means
* it has been freed by this transaction and hence it
* could not have been reallocated until this
* transaction has committed. *BUT* it could be
* reallocated once we have written all the data to
* disk and before we process the buffer on BJ_Forget
- * list. */
- JBUFFER_TRACE(jh, "refile or unfile freed buffer");
- __journal_refile_buffer(jh);
- if (!jh->b_transaction) {
- jbd_unlock_bh_state(bh);
- /* needs a brelse */
- journal_remove_journal_head(bh);
- release_buffer_page(bh);
- } else
- jbd_unlock_bh_state(bh);
+ * list.
+ */
+ if (!jh->b_next_transaction)
+ try_to_free = 1;
}
+ JBUFFER_TRACE(jh, "refile or unfile freed buffer");
+ __journal_refile_buffer(jh);
+ jbd_unlock_bh_state(bh);
+ if (try_to_free)
+ release_buffer_page(bh);
+ else
+ __brelse(bh);
cond_resched_lock(&journal->j_list_lock);
}
spin_unlock(&journal->j_list_lock);
