[compiler-rt] r340178 - [sanitizer] Use private futex operations for BlockingMutex

[Kostya Kortchinsky via llvm-commits]

Author: cryptoad
Date: Mon Aug 20 07:57:58 2018
New Revision: 340178

URL: http://llvm.org/viewvc/llvm-project?rev=340178&view=rev
Log:
[sanitizer] Use private futex operations for BlockingMutex

Summary:
Use `FUTEX_PRIVATE_FLAG` in conjunction with the wait & wake operations
employed by `BlockingMutex`. As far as I can tell, the mutexes are
process-private, and there is an actual performance benefit at employing the
private operations. There should be no downside to switching to it.

Reviewers: eugenis, alekseyshl, dvyukov

Reviewed By: dvyukov

Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D50910

Modified:
    compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux.cc

Modified: compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux.cc?rev=340178&r1=340177&r2=340178&view=diff
==============================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux.cc (original)
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux.cc Mon Aug 20 07:57:58 2018
@@ -117,6 +117,9 @@ struct kernel_timeval {
 // <linux/futex.h> is broken on some linux distributions.
 const int FUTEX_WAIT = 0;
 const int FUTEX_WAKE = 1;
+const int FUTEX_PRIVATE_FLAG = 128;
+const int FUTEX_WAIT_PRIVATE = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;
+const int FUTEX_WAKE_PRIVATE = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;
 #endif  // SANITIZER_LINUX
 
 // Are we using 32-bit or 64-bit Linux syscalls?
@@ -686,7 +689,8 @@ void BlockingMutex::Lock() {
 #elif SANITIZER_NETBSD
     sched_yield(); /* No userspace futex-like synchronization */
 #else
-    internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAIT, MtxSleeping, 0, 0, 0);
+    internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAIT_PRIVATE, MtxSleeping,
+                     0, 0, 0);
 #endif
   }
 }
@@ -701,7 +705,7 @@ void BlockingMutex::Unlock() {
 #elif SANITIZER_NETBSD
                    /* No userspace futex-like synchronization */
 #else
-    internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAKE, 1, 0, 0, 0);
+    internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAKE_PRIVATE, 1, 0, 0, 0);
 #endif
   }
 }