bionic: Fix wrong kernel_id in pthread descriptor after fork()

After forking, the kernel_id field in the phtread_internal_t returned by pthread_self()
is incorrect --- it's the tid from the parent, not the new tid of the
child.

The root cause is that: currently the kernel_id is set by
_init_thread(), which is called in 2 cases:
(1) called by __libc_init_common(). That happens when the execv( ) is
called after fork( ). But when the zygote tries to fork the android
application, the child application doesn't call execv( ), instread, it
tries to call the Java main method directly.
(2) called by pthread_create(). That happens when a new thread is
created.

For the lead thread which is the thread created by fork(), it should
call execv() but it doesn't, as described in (1) above. So its kernel_id
will inherit the parent's kernel_id.

Fixed it in this patch.

Change-Id: I63513e82af40ec5fe51fbb69456b1843e4bc0fc7
Signed-off-by: Chenyang Du <chenyang.du@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
bionic: fix atfork hanlder_mutex deadlock

After applying the kernel_id fix, the system refused to boot up and we
got following crash log:
I/DEBUG   (  113): pid: 618, tid: 618  >>> org.simalliance.openmobileapi.service:remote <<<
I/DEBUG   (  113): signal 16 (SIGSTKFLT), code -6 (?), fault addr --------
I/DEBUG   (  113):  eax fffffe00  ebx b77de994  ecx 00000080  edx 00724002
I/DEBUG   (  113):  esi 00000000  edi 00004000
I/DEBUG   (  113):  xcs 00000073  xds 0000007b  xes 0000007b  xfs 00000000 xss 0000007b
I/DEBUG   (  113):  eip b7761351  ebp bfdf3de8  esp bfdf3dc4  flags 00000202
I/DEBUG   (  113):     #00  eip: 00015351  /system/lib/libc.so
I/DEBUG   (  113):     #01  eip: 0000d13c  /system/lib/libc.so (pthread_mutex_lock)
I/DEBUG   (  113):     #02  eip: 00077b48  /system/lib/libc.so (__bionic_atfork_run_prepare)
I/DEBUG   (  113):     #03  eip: 00052cdb  /system/lib/libc.so (fork)
I/DEBUG   (  113):     #04  eip: 0009ae91  /system/lib/libdvm.so (_Z18dvmOptimizeDexFileillPKcjjb)
I/DEBUG   (  113):     #05  eip: 000819d6  /system/lib/libdvm.so (_Z14dvmJarFileOpenPKcS0_PP7JarFileb)
I/DEBUG   (  113):     #06  eip: 000b175e  /system/lib/libdvm.so (_ZL40Dalvik_dalvik_system_DexFile_openDexFilePKjP6JValue)
I/DEBUG   (  113):     #07  eip: 0011fb94  /system/lib/libdvm.so

Root cause:
The atfork uses the mutex handler_mutex to protect the atfork_head. The
parent will call __bionic_atfork_run_prepare() to lock the handler_mutex,
and need both the parent and child to unlock their own copy of handler_mutex
after fork. At that time, the owner of hanlder_mutex is set as the parent.
If we apply the kernel_id fix, then the child's kernel_id will be set as
child's tid.
The handler_mutex is a recursive lock, and pthread_mutex_unlock(&hander_mutex)
will fail because the mutex owner is the parent, while the current tid
(__get_thread()->kernel_id) is child, not matched with the mutex owner.
At that time, the handler_mutex is left in lock state.If the child wants to
fork other process after than, then it will try to lock handler_mutex, and
then be deadlocked.

Fix:
Since the child has its own copy of vm space from the the parent, the
child space's handler_mutex should be reset to the initialized state.

Change-Id: I3907dd9a153418fb78862f2aa6d0302c375d9e27
Signed-off-by: Jack Ren <jack.ren@intel.com>
Signed-off-by: Chenyang Du <chenyang.du@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>