[Commits] 5db4c9851: Range Locking, shared locks: fix a bug in acquisition of the same lock twice

Sergei Petrunia psergey at askmonty.org
Sat Nov 30 19:03:50 EET 2019


revision-id: 5db4c985188654955350b1417aedb2b6f92774d8 (v5.8-1899-g5db4c9851)
parent(s): 73ff40dcbf0a46228ea02d5103d1331335622794
author: Sergei Petrunia
committer: Sergei Petrunia
timestamp: 2019-11-30 20:03:50 +0300
message:

Range Locking, shared locks: fix a bug in acquisition of the same lock twice

Check for this case: when the same transaction acquires the same lock
twice, the lock should still have m_txnid={the transaction},
m_owners= nullptr.

Failure to maintain this invariant breaks the logic in other code and in
some scenarios we could end up with shared locks with zero owners.

---
 utilities/transactions/range_locking/locktree/treenode.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/utilities/transactions/range_locking/locktree/treenode.cc b/utilities/transactions/range_locking/locktree/treenode.cc
index 029646d18..725991f7d 100644
--- a/utilities/transactions/range_locking/locktree/treenode.cc
+++ b/utilities/transactions/range_locking/locktree/treenode.cc
@@ -140,6 +140,9 @@ void treenode::swap_in_place(treenode *node1, treenode *node2) {
 
 void treenode::add_shared_owner(TXNID txnid) {
     assert(m_is_shared);
+    if (txnid == m_txnid)
+        return; // acquiring a lock on the same range by the same trx
+
     if (m_txnid != TXNID_SHARED) {
         m_owners= new TxnidVector;
         m_owners->insert(m_txnid);
@@ -373,7 +376,9 @@ void treenode::recursive_remove(void) {
 }
 
 void treenode::remove_shared_owner(TXNID txnid) {
+    assert(m_owners->size()>1);
     m_owners->erase(txnid);
+    assert(m_owners->size()>0);
     /* if there is just one owner left, move it to m_txnid */
     if (m_owners->size() == 1)
     {


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