8321075: RISC-V: UseSystemMemoryBarrier lacking proper OS support

Reviewed-by: fyang, yadongwang, luhenry

src/hotspot/os/linux/os_linux.cpp

@@ -85,6 +85,8 @@
 #endif
 
 // put OS-includes here
+# include <ctype.h>
+# include <stdlib.h>
 # include <sys/types.h>
 # include <sys/mman.h>
 # include <sys/stat.h>
@@ -342,6 +344,29 @@ static void next_line(FILE *f) {
   } while (c != '\n' && c != EOF);
 }
 
+void os::Linux::kernel_version(long* major, long* minor) {
+  *major = -1;
+  *minor = -1;
+
+  struct utsname buffer;
+  int ret = uname(&buffer);
+  if (ret != 0) {
+    log_warning(os)("uname(2) failed to get kernel version: %s", os::errno_name(ret));
+    return;
+  }
+
+  char* walker = buffer.release;
+  long* set_v = major;
+  while (*minor == -1 && walker != nullptr) {
+    if (isdigit(walker[0])) {
+      *set_v = strtol(walker, &walker, 10);
+      set_v = minor;
+    } else {
+      ++walker;
+    }
+  }
+}
+
 bool os::Linux::get_tick_information(CPUPerfTicks* pticks, int which_logical_cpu) {
   FILE*         fh;
   uint64_t      userTicks, niceTicks, systemTicks, idleTicks;

src/hotspot/os/linux/os_linux.hpp

@@ -93,6 +93,8 @@ class os::Linux {
     bool     has_steal_ticks;
   };
 
+  static void kernel_version(long* major, long* minor);
+
   // which_logical_cpu=-1 returns accumulated ticks for all cpus.
   static bool get_tick_information(CPUPerfTicks* pticks, int which_logical_cpu);
   static bool _stack_is_executable;

src/hotspot/os/linux/systemMemoryBarrier_linux.cpp

@@ -24,7 +24,7 @@
 
 #include "precompiled.hpp"
 #include "logging/log.hpp"
-#include "runtime/os.hpp"
+#include "os_linux.hpp"
 #include "utilities/debug.hpp"
 #include "utilities/systemMemoryBarrier.hpp"
 
@@ -61,6 +61,18 @@ static long membarrier(int cmd, unsigned int flags, int cpu_id) {
 }
 
 bool LinuxSystemMemoryBarrier::initialize() {
+#if defined(RISCV)
+// RISCV port was introduced in kernel 4.4.
+// 4.4 also made membar private expedited mandatory.
+// But RISCV actually don't support it until 6.9.
+  long major, minor;
+  os::Linux::kernel_version(&major, &minor);
+  if (!(major > 6 || (major == 6 && minor >= 9))) {
+    log_info(os)("Linux kernel %ld.%ld does not support MEMBARRIER PRIVATE_EXPEDITED on RISC-V.",
+                 major, minor);
+    return false;
+  }
+#endif
   long ret = membarrier(MEMBARRIER_CMD_QUERY, 0, 0);
   if (ret < 0) {
     log_info(os)("MEMBARRIER_CMD_QUERY unsupported");