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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#include "sigbushandler.h"
#include "statefile.h"
#include "statebuf.h"
#include <unistd.h>
#include <cstring>
namespace search {
SigBusHandler *SigBusHandler::_instance = nullptr;
namespace {
std::atomic<int> sigBusNesting;
class TryLockGuard
{
bool _gotLock;
public:
TryLockGuard() noexcept
: _gotLock(false)
{
int expzero = 0;
_gotLock = sigBusNesting.compare_exchange_strong(expzero, 1);
}
~TryLockGuard() noexcept {
if (_gotLock) {
sigBusNesting = 0;
}
}
bool gotLock() const noexcept { return _gotLock; }
};
/*
* Write string to standard error using only async signal safe methods.
*/
void
mystderr(const char *msg) noexcept
{
const char *p = msg;
while (*p != '\0') {
++p;
}
write(STDERR_FILENO, msg, static_cast<size_t>(p - msg));
}
}
void
SigBusHandler::trap()
{
struct sigaction sa;
_instance = this;
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = SigBusHandler::forward;
sa.sa_flags = SA_SIGINFO;
sigemptyset(&sa.sa_mask);
sigaddset(&sa.sa_mask, SIGBUS);
sigaction(SIGBUS, &sa, nullptr);
_trapped = true;
}
void
SigBusHandler::untrap()
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
sa.sa_flags = 0;
sigemptyset(&sa.sa_mask);
sigaction(SIGBUS, &sa, nullptr);
_trapped = false;
_instance = nullptr;
}
void
SigBusHandler::forward(int sig, siginfo_t *si, void *ucv)
{
_instance->handle(sig, si, ucv);
}
void
SigBusHandler::handle(int sig, siginfo_t *si, void *ucv)
{
(void) sig;
(void) ucv;
StateBuf sb(_buf, sizeof(_buf));
bool raced = false;
do {
// Protect against multiple threads.
TryLockGuard guard;
if (!guard.gotLock()) {
raced = true;
break;
}
sb.appendKey("state") << "down";
sb.appendTimestamp();
sb.appendKey("operation") << "sigbus";
sb.appendKey("errno") << static_cast<long>(si->si_errno);
sb.appendKey("code") << static_cast<long>(si->si_code);
if (si->si_code != 0) {
sb.appendAddr(si->si_addr);
}
sb << '\n';
// TODO: Report backing store file, for quick diagnostics.
if (_stateFile != nullptr) {
_stateFile->addState(sb.base(), sb.size(), true);
}
_fired = true;
} while (0);
if (raced) {
mystderr("SIGBUS handler call race, ignoring signal\n");
sleep(5);
return;
}
untrap(); // Further bus errors will trigger core dump
if (_unwind != nullptr) {
// Unit test is using siglongjmp based unwinding
sigjmp_buf *unwind = _unwind;
_unwind = nullptr;
siglongjmp(*unwind, 1);
} else {
// Normal case, sleep 3 seconds (i.e. allow main thread to detect
// issue and notify cluster controller) before returning and
// likely core dumping.
sleep(3);
}
}
SigBusHandler::SigBusHandler(StateFile *stateFile)
: _stateFile(stateFile),
_unwind(nullptr),
_trapped(false),
_fired(false)
{
trap();
}
SigBusHandler::~SigBusHandler()
{
untrap();
}
}
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