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
23unsigned long page_size;
24void *guard;
25
26void handler(int signo, siginfo_t *info, void *uctx) {
27  mprotect(guard, page_size, PROT_READ | PROT_WRITE);
28}
29
30int 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