MDEV-27774 fixup: Replace sspin_lock with srw_lock

srw_lock in log_sys.append_prepare() turned out to yield best throughput.
We might try a NUMA aware spin lock implementation later.

storage/innobase/include/log0log.h

@@ -214,7 +214,7 @@ struct log_t
 
 private:
   /** spin lock protecting lsn, buf_free in append_prepare() */
-  MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE) sspin_lock lsn_lock;
+  MY_ALIGNED(CPU_LEVEL1_DCACHE_LINESIZE) srw_mutex lsn_lock;
 public:
   /** first free offset within buf use; protected by lsn_lock */
   Atomic_relaxed<size_t> buf_free;

storage/innobase/include/srw_lock.h

@@ -520,12 +520,3 @@ typedef srw_lock_impl<false> srw_lock;
 typedef srw_lock_impl<true> srw_spin_lock;
 
 #endif
-
-/** Simple spin lock */
-struct sspin_lock
-{
-  std::atomic<uint32_t> word{0};
-  void lock() noexcept;
-  void unlock() noexcept
-  { ut_ad(word); word.store(0, std::memory_order_release); }
-};

storage/innobase/log/log0log.cc

@@ -101,6 +101,7 @@ void log_t::create()
   ut_ad(!is_initialised());
 
   latch.SRW_LOCK_INIT(log_latch_key);
+  lsn_lock.init();
 
   /* LSN 0 and 1 are reserved; @see buf_page_t::oldest_modification_ */
   lsn.store(FIRST_LSN, std::memory_order_relaxed);
@@ -1070,6 +1071,7 @@ void log_t::close()
 #endif
 
   latch.destroy();
+  lsn_lock.destroy();
 
   recv_sys.close();
 

storage/innobase/mtr/mtr0mtr.cc

@@ -789,7 +789,7 @@ ATTRIBUTE_COLD static void log_overwrite_warning(lsn_t age, lsn_t capacity)
 ATTRIBUTE_COLD void log_t::append_prepare_wait(bool ex) noexcept
 {
   log_sys.waits++;
-  log_sys.lsn_lock.unlock();
+  log_sys.lsn_lock.wr_unlock();
 
   if (ex)
     log_sys.latch.wr_unlock();
@@ -804,7 +804,7 @@ ATTRIBUTE_COLD void log_t::append_prepare_wait(bool ex) noexcept
   else
     log_sys.latch.rd_lock(SRW_LOCK_CALL);
 
-  log_sys.lsn_lock.lock();
+  log_sys.lsn_lock.wr_lock();
 }
 
 /** Reserve space in the log buffer for appending data.
@@ -823,7 +823,7 @@ std::pair<lsn_t,byte*> log_t::append_prepare(size_t size, bool ex) noexcept
 #endif
   const lsn_t checkpoint_margin{last_checkpoint_lsn + log_capacity - size};
   const size_t avail{(pmem ? size_t(capacity()) : buf_size) - size};
-  lsn_lock.lock();
+  lsn_lock.wr_lock(); /* Just use SRWLOCK or pthread_mutex_t */
   write_to_buf++;
 
   for (ut_d(int count= 50);
@@ -844,7 +844,7 @@ std::pair<lsn_t,byte*> log_t::append_prepare(size_t size, bool ex) noexcept
   if (pmem && new_buf_free >= file_size)
     new_buf_free-= size_t(capacity());
   buf_free= new_buf_free;
-  lsn_lock.unlock();
+  lsn_lock.wr_unlock();
 
   if (UNIV_UNLIKELY(l > checkpoint_margin) ||
       (!pmem && b >= max_buf_free))

storage/innobase/sync/srw_lock.cc

@@ -102,13 +102,6 @@ static inline void srw_pause(unsigned delay)
   HMT_medium();
 }
 
-void sspin_lock::lock() noexcept
-{
-  while (word.exchange(true, std::memory_order_acquire))
-    while (word.load(std::memory_order_relaxed))
-      srw_pause(1);
-}
-
 #ifdef SUX_LOCK_GENERIC
 template<> void srw_mutex_impl<true>::wr_wait()
 {