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      1 /*
      2  * Copyright (C) 2010 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include "sigchld_handler.h"
     18 
     19 #include <signal.h>
     20 #include <string.h>
     21 #include <sys/socket.h>
     22 #include <sys/types.h>
     23 #include <sys/wait.h>
     24 #include <unistd.h>
     25 
     26 #include <android-base/chrono_utils.h>
     27 #include <android-base/logging.h>
     28 #include <android-base/scopeguard.h>
     29 #include <android-base/stringprintf.h>
     30 
     31 #include "init.h"
     32 #include "property_service.h"
     33 #include "service.h"
     34 
     35 using android::base::StringPrintf;
     36 using android::base::boot_clock;
     37 using android::base::make_scope_guard;
     38 
     39 namespace android {
     40 namespace init {
     41 
     42 static int signal_write_fd = -1;
     43 static int signal_read_fd = -1;
     44 
     45 static bool ReapOneProcess() {
     46     siginfo_t siginfo = {};
     47     // This returns a zombie pid or informs us that there are no zombies left to be reaped.
     48     // It does NOT reap the pid; that is done below.
     49     if (TEMP_FAILURE_RETRY(waitid(P_ALL, 0, &siginfo, WEXITED | WNOHANG | WNOWAIT)) != 0) {
     50         PLOG(ERROR) << "waitid failed";
     51         return false;
     52     }
     53 
     54     auto pid = siginfo.si_pid;
     55     if (pid == 0) return false;
     56 
     57     // At this point we know we have a zombie pid, so we use this scopeguard to reap the pid
     58     // whenever the function returns from this point forward.
     59     // We do NOT want to reap the zombie earlier as in Service::Reap(), we kill(-pid, ...) and we
     60     // want the pid to remain valid throughout that (and potentially future) usages.
     61     auto reaper = make_scope_guard([pid] { TEMP_FAILURE_RETRY(waitpid(pid, nullptr, WNOHANG)); });
     62 
     63     std::string name;
     64     std::string wait_string;
     65     Service* service = nullptr;
     66 
     67     if (PropertyChildReap(pid)) {
     68         name = "Async property child";
     69     } else if (SubcontextChildReap(pid)) {
     70         name = "Subcontext";
     71     } else {
     72         service = ServiceList::GetInstance().FindService(pid, &Service::pid);
     73 
     74         if (service) {
     75             name = StringPrintf("Service '%s' (pid %d)", service->name().c_str(), pid);
     76             if (service->flags() & SVC_EXEC) {
     77                 auto exec_duration = boot_clock::now() - service->time_started();
     78                 auto exec_duration_ms =
     79                     std::chrono::duration_cast<std::chrono::milliseconds>(exec_duration).count();
     80                 wait_string = StringPrintf(" waiting took %f seconds", exec_duration_ms / 1000.0f);
     81             }
     82         } else {
     83             name = StringPrintf("Untracked pid %d", pid);
     84         }
     85     }
     86 
     87     if (siginfo.si_code == CLD_EXITED) {
     88         LOG(INFO) << name << " exited with status " << siginfo.si_status << wait_string;
     89     } else {
     90         LOG(INFO) << name << " received signal " << siginfo.si_status << wait_string;
     91     }
     92 
     93     if (!service) return true;
     94 
     95     service->Reap(siginfo);
     96 
     97     if (service->flags() & SVC_TEMPORARY) {
     98         ServiceList::GetInstance().RemoveService(*service);
     99     }
    100 
    101     return true;
    102 }
    103 
    104 static void handle_signal() {
    105     // Clear outstanding requests.
    106     char buf[32];
    107     read(signal_read_fd, buf, sizeof(buf));
    108 
    109     ReapAnyOutstandingChildren();
    110 }
    111 
    112 static void SIGCHLD_handler(int) {
    113     if (TEMP_FAILURE_RETRY(write(signal_write_fd, "1", 1)) == -1) {
    114         PLOG(ERROR) << "write(signal_write_fd) failed";
    115     }
    116 }
    117 
    118 void ReapAnyOutstandingChildren() {
    119     while (ReapOneProcess()) {
    120     }
    121 }
    122 
    123 void sigchld_handler_init() {
    124     // Create a signalling mechanism for SIGCHLD.
    125     int s[2];
    126     if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0, s) == -1) {
    127         PLOG(FATAL) << "socketpair failed in sigchld_handler_init";
    128     }
    129 
    130     signal_write_fd = s[0];
    131     signal_read_fd = s[1];
    132 
    133     // Write to signal_write_fd if we catch SIGCHLD.
    134     struct sigaction act;
    135     memset(&act, 0, sizeof(act));
    136     act.sa_handler = SIGCHLD_handler;
    137     act.sa_flags = SA_NOCLDSTOP;
    138     sigaction(SIGCHLD, &act, 0);
    139 
    140     ReapAnyOutstandingChildren();
    141 
    142     register_epoll_handler(signal_read_fd, handle_signal);
    143 }
    144 
    145 }  // namespace init
    146 }  // namespace android
    147