56 lines · cpp
1// RUN: %clangxx -O1 %s -o %t && env TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" %run %t 2>&1 | FileCheck %s2 3// JVM uses SEGV to preempt threads. All threads do a load from a known address4// periodically. When runtime needs to preempt threads, it unmaps the page.5// Threads start triggering SEGV one by one. The signal handler blocks6// threads while runtime does its thing. Then runtime maps the page again7// 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 of13// "benign" SEGVs that are handled by signal handler, and ensures that14// 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 24unsigned long page_size;25void *guard;26 27void handler(int signo, siginfo_t *info, void *uctx) {28 mprotect(guard, page_size, PROT_READ | PROT_WRITE);29}30 31int 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: DONE56