Add wchan data to ANR dump
Since only privileged processes with CAP_SYS_ADMIN can read kernel
stack traces from /proc/*/stack, we dump the waiting channels
instead to provide some insight as to where the process might
be stuck in the kernel.
Bug: 135458700
Fixes: 135458700
Test: adb shell am hang; Check /data/anr/<anr-file> for
wchan data.
Change-Id: I9f13511ad89a259ce5e5465155db15d45d2c46d8
diff --git a/debuggerd/client/debuggerd_client.cpp b/debuggerd/client/debuggerd_client.cpp
index 60eb241..1a5b435 100644
--- a/debuggerd/client/debuggerd_client.cpp
+++ b/debuggerd/client/debuggerd_client.cpp
@@ -22,9 +22,11 @@
#include <sys/poll.h>
#include <sys/stat.h>
#include <sys/types.h>
+#include <time.h>
#include <unistd.h>
#include <chrono>
+#include <iomanip>
#include <android-base/cmsg.h>
#include <android-base/file.h>
@@ -42,8 +44,10 @@
using namespace std::chrono_literals;
+using android::base::ReadFileToString;
using android::base::SendFileDescriptors;
using android::base::unique_fd;
+using android::base::WriteStringToFd;
static bool send_signal(pid_t pid, const DebuggerdDumpType dump_type) {
const int signal = (dump_type == kDebuggerdJavaBacktrace) ? SIGQUIT : DEBUGGER_SIGNAL;
@@ -65,6 +69,76 @@
tv->tv_usec = static_cast<long>(microseconds.count());
}
+static void get_wchan_header(pid_t pid, std::stringstream& buffer) {
+ struct tm now;
+ time_t t = time(nullptr);
+ localtime_r(&t, &now);
+ char timestamp[32];
+ strftime(timestamp, sizeof(timestamp), "%Y-%m-%d %H:%M:%S", &now);
+ std::string time_now(timestamp);
+
+ std::string path = "/proc/" + std::to_string(pid) + "/cmdline";
+
+ char proc_name_buf[1024];
+ const char* proc_name = nullptr;
+ std::unique_ptr<FILE, decltype(&fclose)> fp(fopen(path.c_str(), "r"), &fclose);
+
+ if (fp) {
+ proc_name = fgets(proc_name_buf, sizeof(proc_name_buf), fp.get());
+ }
+
+ if (!proc_name) {
+ proc_name = "<unknown>";
+ }
+
+ buffer << "\n----- Waiting Channels: pid " << pid << " at " << time_now << " -----\n"
+ << "Cmd line: " << proc_name << "\n";
+}
+
+static void get_wchan_footer(pid_t pid, std::stringstream& buffer) {
+ buffer << "----- end " << std::to_string(pid) << " -----\n";
+}
+
+/**
+ * Returns the wchan data for each thread in the process,
+ * or empty string if unable to obtain any data.
+ */
+static std::string get_wchan_data(pid_t pid) {
+ std::stringstream buffer;
+ std::vector<pid_t> tids;
+
+ if (!android::procinfo::GetProcessTids(pid, &tids)) {
+ LOG(WARNING) << "libdebuggerd_client: Failed to get process tids";
+ return buffer.str();
+ }
+
+ std::stringstream data;
+ for (int tid : tids) {
+ std::string path = "/proc/" + std::to_string(pid) + "/task/" + std::to_string(tid) + "/wchan";
+ std::string wchan_str;
+ if (!ReadFileToString(path, &wchan_str, true)) {
+ PLOG(WARNING) << "libdebuggerd_client: Failed to read \"" << path << "\"";
+ continue;
+ }
+ data << "sysTid=" << std::left << std::setw(10) << tid << wchan_str << "\n";
+ }
+
+ if (std::string str = data.str(); !str.empty()) {
+ get_wchan_header(pid, buffer);
+ buffer << "\n" << str << "\n";
+ get_wchan_footer(pid, buffer);
+ buffer << "\n";
+ }
+
+ return buffer.str();
+}
+
+static void dump_wchan_data(const std::string& data, int fd, pid_t pid) {
+ if (!WriteStringToFd(data, fd)) {
+ LOG(WARNING) << "libdebuggerd_client: Failed to dump wchan data for pid: " << pid;
+ }
+}
+
bool debuggerd_trigger_dump(pid_t tid, DebuggerdDumpType dump_type, unsigned int timeout_ms,
unique_fd output_fd) {
pid_t pid = tid;
@@ -261,6 +335,17 @@
if (copy == -1) {
return -1;
}
+
+ // debuggerd_trigger_dump results in every thread in the process being interrupted
+ // by a signal, so we need to fetch the wchan data before calling that.
+ std::string wchan_data = get_wchan_data(tid);
+
int timeout_ms = timeout_secs > 0 ? timeout_secs * 1000 : 0;
- return debuggerd_trigger_dump(tid, dump_type, timeout_ms, std::move(copy)) ? 0 : -1;
+ int ret = debuggerd_trigger_dump(tid, dump_type, timeout_ms, std::move(copy)) ? 0 : -1;
+
+ // Dump wchan data, since only privileged processes (CAP_SYS_ADMIN) can read
+ // kernel stack traces (/proc/*/stack).
+ dump_wchan_data(wchan_data, fd, tid);
+
+ return ret;
}