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Merge "Fix getpid caching across a clone."

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Elliott Hughes 2014-06-24 16:36:31 +00:00 committed by Gerrit Code Review
commit 598f4b3ac1
2 changed files with 47 additions and 7 deletions
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17
libc/bionic/clone.cpp
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@ -31,6 +31,8 @@
#include <stdlib.h>
#include <stdarg.h>
#include "pthread_internal.h"
extern "C" pid_t __bionic_clone(uint32_t flags, void* child_stack, int* parent_tid, void* tls, int* child_tid, int (*fn)(void*), void* arg);
extern "C" __noreturn void __exit(int status);
@ -64,5 +66,18 @@ int clone(int (*fn)(void*), void* child_stack, int flags, void* arg, ...) {
child_stack_addr &= ~0xf;
child_stack = reinterpret_cast<void*>(child_stack_addr);
return __bionic_clone(flags, child_stack, parent_tid, new_tls, child_tid, fn, arg);
// Remember the parent pid and invalidate the cached value while we clone.
pthread_internal_t* self = __get_thread();
pid_t parent_pid = self->invalidate_cached_pid();
// Actually do the clone.
int clone_result = __bionic_clone(flags, child_stack, parent_tid, new_tls, child_tid, fn, arg);
// We're the parent, so put our known pid back in place.
// We leave the child without a cached pid, but:
// 1. pthread_create gives its children their own pthread_internal_t with the correct pid.
// 2. fork makes a clone system call directly.
// If any other cases become important, we could use a double trampoline like __pthread_start.
self->set_cached_pid(parent_pid);
return clone_result;
}

37
tests/unistd_test.cpp
View file

@ -381,6 +381,14 @@ TEST(unistd, fsync) {
TestFsyncFunction(fsync);
}
static void AssertGetPidCorrect() {
// The loop is just to make manual testing/debugging with strace easier.
pid_t getpid_syscall_result = syscall(__NR_getpid);
for (size_t i = 0; i < 128; ++i) {
ASSERT_EQ(getpid_syscall_result, getpid());
}
}
TEST(unistd, getpid_caching_and_fork) {
pid_t parent_pid = getpid();
ASSERT_EQ(syscall(__NR_getpid), parent_pid);
@ -389,7 +397,7 @@ TEST(unistd, getpid_caching_and_fork) {
ASSERT_NE(fork_result, -1);
if (fork_result == 0) {
// We're the child.
ASSERT_EQ(syscall(__NR_getpid), getpid());
AssertGetPidCorrect();
ASSERT_EQ(parent_pid, getppid());
_exit(123);
} else {
@ -403,12 +411,29 @@ TEST(unistd, getpid_caching_and_fork) {
}
}
static void GetPidCachingHelperHelper() {
ASSERT_EQ(syscall(__NR_getpid), getpid());
static int GetPidCachingCloneStartRoutine(void*) {
AssertGetPidCorrect();
return 123;
}
static void* GetPidCachingHelper(void*) {
GetPidCachingHelperHelper(); // Can't assert in a non-void function.
TEST(unistd, getpid_caching_and_clone) {
pid_t parent_pid = getpid();
ASSERT_EQ(syscall(__NR_getpid), parent_pid);
void* child_stack[1024];
int clone_result = clone(GetPidCachingCloneStartRoutine, &child_stack[1024], CLONE_NEWNS | SIGCHLD, NULL);
ASSERT_NE(clone_result, -1);
ASSERT_EQ(parent_pid, getpid());
int status;
ASSERT_EQ(clone_result, waitpid(clone_result, &status, 0));
ASSERT_TRUE(WIFEXITED(status));
ASSERT_EQ(123, WEXITSTATUS(status));
}
static void* GetPidCachingPthreadStartRoutine(void*) {
AssertGetPidCorrect();
return NULL;
}
@ -416,7 +441,7 @@ TEST(unistd, getpid_caching_and_pthread_create) {
pid_t parent_pid = getpid();
pthread_t t;
ASSERT_EQ(0, pthread_create(&t, NULL, GetPidCachingHelper, NULL));
ASSERT_EQ(0, pthread_create(&t, NULL, GetPidCachingPthreadStartRoutine, NULL));
ASSERT_EQ(parent_pid, getpid());