1 // RUN: %clangxx -O1 %s -o %t && env TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" %run %t 2>&1 | FileCheck %s 2 3 // JVM uses SEGV to preempt threads. All threads do a load from a known address 4 // periodically. When runtime needs to preempt threads, it unmaps the page. 5 // Threads start triggering SEGV one by one. The signal handler blocks 6 // threads while runtime does its thing. Then runtime maps the page again 7 // and resumes the threads. 8 // Previously this pattern conflicted with stop-the-world machinery, 9 // because it briefly reset SEGV handler to SIG_DFL. 10 // As the consequence JVM just silently died. 11 12 // This test sets memory flushing rate to maximum, then does series of 13 // "benign" SEGVs that are handled by signal handler, and ensures that 14 // the process survive. 15 16 #include <assert.h> 17 #include <signal.h> 18 #include <stdio.h> 19 #include <stdlib.h> 20 #include <string.h> 21 #include <sys/mman.h> 22 #include <unistd.h> 23 24 unsigned long page_size; 25 void *guard; 26 27 void handler(int signo, siginfo_t *info, void *uctx) { 28 mprotect(guard, page_size, PROT_READ | PROT_WRITE); 29 } 30 31 int main() { 32 page_size = sysconf(_SC_PAGESIZE); 33 struct sigaction a, old; 34 memset(&a, 0, sizeof(a)); 35 memset(&old, 0, sizeof(old)); 36 a.sa_sigaction = handler; 37 a.sa_flags = SA_SIGINFO; 38 sigaction(SIGSEGV, &a, &old); 39 40 memset(&a, 0, sizeof(a)); 41 sigaction(SIGSEGV, 0, &a); 42 assert(a.sa_sigaction == handler); 43 assert(a.sa_flags & SA_SIGINFO); 44 45 guard = mmap(0, 3 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0); 46 guard = (char*)guard + page_size; // work around a kernel bug 47 for (int i = 0; i < 1000000; i++) { 48 mprotect(guard, page_size, PROT_NONE); 49 *(int*)guard = 1; 50 } 51 sigaction(SIGSEGV, &old, 0); 52 fprintf(stderr, "DONE\n"); 53 } 54 55 // CHECK: DONE 56