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/
I/DEBUG   (  113):     #01  eip: 0000d13c  /system/lib/ (pthread_mutex_lock)
I/DEBUG   (  113):     #02  eip: 00077b48  /system/lib/ (__bionic_atfork_run_prepare)
I/DEBUG   (  113):     #03  eip: 00052cdb  /system/lib/ (fork)
I/DEBUG   (  113):     #04  eip: 0009ae91  /system/lib/ (_Z18dvmOptimizeDexFileillPKcjjb)
I/DEBUG   (  113):     #05  eip: 000819d6  /system/lib/ (_Z14dvmJarFileOpenPKcS0_PP7JarFileb)
I/DEBUG   (  113):     #06  eip: 000b175e  /system/lib/ (_ZL40Dalvik_dalvik_system_DexFile_openDexFilePKjP6JValue)
I/DEBUG   (  113):     #07  eip: 0011fb94  /system/lib/

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.

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 <>
Signed-off-by: Chenyang Du <>
Signed-off-by: Bruce Beare <>
1 file changed