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-rw-r--r--fs/jbd2/transaction.c76
1 files changed, 72 insertions, 4 deletions
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 1bbcf86499c9..f3d06174b051 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -892,6 +892,12 @@ repeat:
JBUFFER_TRACE(jh, "no transaction");
J_ASSERT_JH(jh, !jh->b_next_transaction);
JBUFFER_TRACE(jh, "file as BJ_Reserved");
+ /*
+ * Make sure all stores to jh (b_modified, b_frozen_data) are
+ * visible before attaching it to the running transaction.
+ * Paired with barrier in jbd2_write_access_granted()
+ */
+ smp_wmb();
spin_lock(&journal->j_list_lock);
__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
spin_unlock(&journal->j_list_lock);
@@ -904,8 +910,7 @@ repeat:
if (jh->b_frozen_data) {
JBUFFER_TRACE(jh, "has frozen data");
J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
- jh->b_next_transaction = transaction;
- goto done;
+ goto attach_next;
}
JBUFFER_TRACE(jh, "owned by older transaction");
@@ -959,6 +964,13 @@ repeat:
frozen_buffer = NULL;
jbd2_freeze_jh_data(jh);
}
+attach_next:
+ /*
+ * Make sure all stores to jh (b_modified, b_frozen_data) are visible
+ * before attaching it to the running transaction. Paired with barrier
+ * in jbd2_write_access_granted()
+ */
+ smp_wmb();
jh->b_next_transaction = transaction;
done:
@@ -978,6 +990,55 @@ out:
return error;
}
+/* Fast check whether buffer is already attached to the required transaction */
+static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh)
+{
+ struct journal_head *jh;
+ bool ret = false;
+
+ /* Dirty buffers require special handling... */
+ if (buffer_dirty(bh))
+ return false;
+
+ /*
+ * RCU protects us from dereferencing freed pages. So the checks we do
+ * are guaranteed not to oops. However the jh slab object can get freed
+ * & reallocated while we work with it. So we have to be careful. When
+ * we see jh attached to the running transaction, we know it must stay
+ * so until the transaction is committed. Thus jh won't be freed and
+ * will be attached to the same bh while we run. However it can
+ * happen jh gets freed, reallocated, and attached to the transaction
+ * just after we get pointer to it from bh. So we have to be careful
+ * and recheck jh still belongs to our bh before we return success.
+ */
+ rcu_read_lock();
+ if (!buffer_jbd(bh))
+ goto out;
+ /* This should be bh2jh() but that doesn't work with inline functions */
+ jh = READ_ONCE(bh->b_private);
+ if (!jh)
+ goto out;
+ if (jh->b_transaction != handle->h_transaction &&
+ jh->b_next_transaction != handle->h_transaction)
+ goto out;
+ /*
+ * There are two reasons for the barrier here:
+ * 1) Make sure to fetch b_bh after we did previous checks so that we
+ * detect when jh went through free, realloc, attach to transaction
+ * while we were checking. Paired with implicit barrier in that path.
+ * 2) So that access to bh done after jbd2_write_access_granted()
+ * doesn't get reordered and see inconsistent state of concurrent
+ * do_get_write_access().
+ */
+ smp_mb();
+ if (unlikely(jh->b_bh != bh))
+ goto out;
+ ret = true;
+out:
+ rcu_read_unlock();
+ return ret;
+}
+
/**
* int jbd2_journal_get_write_access() - notify intent to modify a buffer for metadata (not data) update.
* @handle: transaction to add buffer modifications to
@@ -991,9 +1052,13 @@ out:
int jbd2_journal_get_write_access(handle_t *handle, struct buffer_head *bh)
{
- struct journal_head *jh = jbd2_journal_add_journal_head(bh);
+ struct journal_head *jh;
int rc;
+ if (jbd2_write_access_granted(handle, bh))
+ return 0;
+
+ jh = jbd2_journal_add_journal_head(bh);
/* We do not want to get caught playing with fields which the
* log thread also manipulates. Make sure that the buffer
* completes any outstanding IO before proceeding. */
@@ -1123,11 +1188,14 @@ out:
int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
{
int err;
- struct journal_head *jh = jbd2_journal_add_journal_head(bh);
+ struct journal_head *jh;
char *committed_data = NULL;
JBUFFER_TRACE(jh, "entry");
+ if (jbd2_write_access_granted(handle, bh))
+ return 0;
+ jh = jbd2_journal_add_journal_head(bh);
/*
* Do this first --- it can drop the journal lock, so we want to
* make sure that obtaining the committed_data is done