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
handler(int signo,siginfo_t * info,void * uctx)26 void handler(int signo, siginfo_t *info, void *uctx) {
27 mprotect(guard, page_size, PROT_READ | PROT_WRITE);
28 }
29
main()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