From 7c524d4414e1608a54a8affbcce35d08c1ceaa59 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marko=20M=C3=A4kel=C3=A4?= <marko.makela@mariadb.com>
Date: Thu, 8 Apr 2021 13:32:16 +0300
Subject: [PATCH] MDEV-25371 Potential hang in wsrep_is_BF_lock_timeout()
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In commit e71e6133535da8d5eab86e504f0b116a03680780 (MDEV-24671),
lock_sys.wait_mutex was moved above lock_sys.mutex
(which was later replaced with lock_sys.latch) in the latching order.

In commit 7cf4419fc4874a31d6242699dadbfe470ce5626c (MDEV-24789),
a potential hang was introduced to Galera. The function lock_wait()
would hold lock_sys.wait_mutex while invoking wsrep_is_BF_lock_timeout(),
which in turn could acquire LockMutexGuard for some diagnostic printout.

wsrep_is_BF_lock_timeout(): Do not invoke trx_print_latched() or
LockMutexGuard.

lock_sys_t::wr_lock(), lock_sys_t::rd_lock(): Assert that the current
thread is not holding lock_sys.wait_mutex.
Unfortunately, RW-locks are not covered by SAFE_MUTEX.

Reviewed by: Jan Lindström
---
 storage/innobase/include/lock0lock.h | 2 ++
 storage/innobase/lock/lock0lock.cc   | 6 ++----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/storage/innobase/include/lock0lock.h b/storage/innobase/include/lock0lock.h
index c3b802f4284..8e38b99c121 100644
--- a/storage/innobase/include/lock0lock.h
+++ b/storage/innobase/include/lock0lock.h
@@ -703,6 +703,7 @@ public:
   /** Acquire exclusive lock_sys.latch */
   void wr_lock()
   {
+    mysql_mutex_assert_not_owner(&wait_mutex);
     ut_ad(!is_writer());
     latch.wr_lock();
     ut_ad(!writer.exchange(os_thread_get_curr_id(),
@@ -718,6 +719,7 @@ public:
   /** Acquire shared lock_sys.latch */
   void rd_lock()
   {
+    mysql_mutex_assert_not_owner(&wait_mutex);
     ut_ad(!is_writer());
     latch.rd_lock();
     ut_ad(!writer.load(std::memory_order_relaxed));
diff --git a/storage/innobase/lock/lock0lock.cc b/storage/innobase/lock/lock0lock.cc
index 7c266eccb3c..756902690c2 100644
--- a/storage/innobase/lock/lock0lock.cc
+++ b/storage/innobase/lock/lock0lock.cc
@@ -391,6 +391,7 @@ void lock_sys_t::create(ulint n_cells)
 /** Acquire exclusive lock_sys.latch */
 void lock_sys_t::wr_lock(const char *file, unsigned line)
 {
+  mysql_mutex_assert_not_owner(&wait_mutex);
   latch.wr_lock(file, line);
   ut_ad(!writer.exchange(os_thread_get_curr_id(), std::memory_order_relaxed));
 }
@@ -405,6 +406,7 @@ void lock_sys_t::wr_unlock()
 /** Acquire shared lock_sys.latch */
 void lock_sys_t::rd_lock(const char *file, unsigned line)
 {
+  mysql_mutex_assert_not_owner(&wait_mutex);
   latch.rd_lock(file, line);
   ut_ad(!writer.load(std::memory_order_relaxed));
   ut_d(readers.fetch_add(1, std::memory_order_relaxed));
@@ -549,10 +551,6 @@ ATTRIBUTE_NOINLINE static bool wsrep_is_BF_lock_timeout(const trx_t &trx)
 
   ib::info() << "WSREP: BF lock wait long for trx:" << ib::hex(trx.id)
              << " query: " << wsrep_thd_query(trx.mysql_thd);
-  {
-    LockMutexGuard g{SRW_LOCK_CALL};
-    trx_print_latched(stderr, &trx, 3000);
-  }
 
   srv_print_innodb_monitor= true;
   srv_print_innodb_lock_monitor= true;