hcq/MaxScale
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MXS-3059: Don't use STL containers concurrently

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The diagnostics_json call could access the std::unordered_map at the same
time it was being updated by the monitoring thread. This leads to
undefined behavior which in the case of MXS-3059 manifested as a segfault.
This commit is contained in:
Markus Mäkelä 2020-07-03 07:26:53 +03:00
parent ad4bd26ff0
commit 7520efd218
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GPG Key ID: 5CE746D557ACC499
2 changed files with 10 additions and 3 deletions
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9
server/modules/monitor/galeramon/galeramon.cc
View File

@ -103,12 +103,13 @@ json_t* GaleraMonitor::diagnostics_json() const
}
json_t* arr = json_array();
std::lock_guard<std::mutex> guard(m_lock);
for (auto ptr : servers())
{
auto it = m_info.find(ptr);
auto it = m_prev_info.find(ptr);
if (it != m_info.end())
if (it != m_prev_info.end())
{
json_t* obj = json_object();
json_object_set_new(obj, "name", json_string(it->first->server->name()));
@ -357,7 +358,9 @@ void GaleraMonitor::calculate_cluster()
void GaleraMonitor::pre_tick()
{
// Clear the info before monitoring to make sure it's up to date
// Store the info of the previous tick in case it's used for diagnostics
std::lock_guard<std::mutex> guard(m_lock);
m_prev_info = std::move(m_info);
m_info.clear();
}

4
server/modules/monitor/galeramon/galeramon.hh
View File

@ -69,8 +69,12 @@ private:
std::string m_cluster_uuid; /**< The Cluster UUID */
bool m_log_no_members; /**< Should we log if no member are found. */
NodeMap m_info; /**< Contains Galera Cluster variables of all nodes */
NodeMap m_prev_info; /**< Contains the info from the previous tick */
int m_cluster_size; /**< How many nodes in the cluster */
// Prevents concurrent use that might occur during the diagnostics_json call
mutable std::mutex m_lock;
GaleraMonitor(const std::string& name, const std::string& module);
bool detect_cluster_size(const int n_nodes,