1 // RUN: %clangxx -O1 %s -o %t && TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" ASAN_OPTIONS="handle_segv=0 allow_user_segv_handler=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 <stdio.h> 17 #include <stdlib.h> 18 #include <signal.h> 19 #include <sys/mman.h> 20 #include <string.h> 21 #include <unistd.h> 22 23 unsigned long page_size; 24 void *guard; 25 26 void handler(int signo, siginfo_t *info, void *uctx) { 27 mprotect(guard, page_size, PROT_READ | PROT_WRITE); 28 } 29 30 int main() { 31 page_size = sysconf(_SC_PAGESIZE); 32 struct sigaction a, old; 33 memset(&a, 0, sizeof(a)); 34 memset(&old, 0, sizeof(old)); 35 a.sa_sigaction = handler; 36 a.sa_flags = SA_SIGINFO; 37 sigaction(SIGSEGV, &a, &old); 38 guard = mmap(0, 3 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0); 39 guard = (char*)guard + page_size; // work around a kernel bug 40 for (int i = 0; i < 1000000; i++) { 41 mprotect(guard, page_size, PROT_NONE); 42 *(int*)guard = 1; 43 } 44 sigaction(SIGSEGV, &old, 0); 45 fprintf(stderr, "DONE\n"); 46 } 47 48 // CHECK: DONE 49
