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debuggerd_handler: actually wait for pseudothread to exit.

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Occasionally, the pseudothread wouldn't exit in time after unlocking
the mutex to get crash_dump to proceed, resulting in spurious error
messages. Instead of using a mutex to emulate pthread_join, just
implement it correctly.

Bug: http://b/34472671
Test: debuggerd_test
Change-Id: I5c2658a84e9407ed8cc0ef2ad0fb648c388b7ad1
This commit is contained in:
Josh Gao 2017-01-22 18:22:52 -08:00
parent 13c15e05d0
commit b64dd85c94
1 changed files with 13 additions and 9 deletions
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22
debuggerd/handler/debuggerd_handler.cpp
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@ -31,6 +31,7 @@
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <linux/futex.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
@ -46,6 +47,7 @@
#include <sys/wait.h>
#include <unistd.h>
#include "private/bionic_futex.h"
#include "private/libc_logging.h"
// see man(2) prctl, specifically the section about PR_GET_NAME
@ -151,7 +153,6 @@ static bool have_siginfo(int signum) {
}
struct debugger_thread_info {
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
bool crash_dump_started = false;
pid_t crashing_tid;
pid_t pseudothread_tid;
@ -228,7 +229,7 @@ static int debuggerd_dispatch_pseudothread(void* arg) {
}
}
pthread_mutex_unlock(&thread_info->mutex);
syscall(__NR_exit, 0);
return 0;
}
@ -267,23 +268,26 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*)
}
debugger_thread_info thread_info = {
.pseudothread_tid = -1,
.crashing_tid = gettid(),
.signal_number = signal_number,
.info = info
};
pthread_mutex_lock(&thread_info.mutex);
// Essentially pthread_create without CLONE_FILES (see debuggerd_dispatch_pseudothread).
pid_t child_pid = clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID,
&thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
pid_t child_pid =
clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
&thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
if (child_pid == -1) {
fatal("failed to spawn debuggerd dispatch thread: %s", strerror(errno));
}
// Wait for the child to finish and unlock the mutex.
// This relies on bionic behavior that isn't guaranteed by the standard.
pthread_mutex_lock(&thread_info.mutex);
// Wait for the child to start...
__futex_wait(&thread_info.pseudothread_tid, -1, nullptr);
// and then wait for it to finish.
__futex_wait(&thread_info.pseudothread_tid, child_pid, nullptr);
// Signals can either be fatal or nonfatal.
// For fatal signals, crash_dump will PTRACE_CONT us with the signal we