Another release, another attempt to fix this bug.
This change affects pthread_detach, pthread_getcpuclockid,
pthread_getschedparam/pthread_setschedparam, pthread_join, and pthread_kill:
instead of returning ESRCH when passed an invalid pthread_t, they'll now SEGV.
Note that this doesn't change behavior as much as you might think: the old
lookup only held the global thread list lock for the duration of the lookup,
so there was still a race between that and the dereference in the caller,
given that callers actually need the tid to pass to some syscall or other,
and sometimes update fields in the pthread_internal_t struct too.
We can't check thread->tid against 0 to see whether a pthread_t is still
valid because a dead thread gets its thread struct unmapped along with its
stack, so the dereference isn't safe.
Taking the affected functions one by one:
* pthread_getcpuclockid and pthread_getschedparam/pthread_setschedparam
should be fine. Unsafe calls to those seem highly unlikely.
* Unsafe pthread_detach callers probably want to switch to
pthread_attr_setdetachstate instead, or using pthread_detach(pthread_self())
from the new thread's start routine rather than doing the detach in the
parent.
* pthread_join calls should be safe anyway, because a joinable thread won't
actually exit and unmap until it's joined. If you're joining an
unjoinable thread, the fix is to stop marking it detached. If you're
joining an already-joined thread, you need to rethink your design.
* Unsafe pthread_kill calls aren't portably fixable. (And are obviously
inherently non-portable as-is.) The best alternative on Android is to
use pthread_gettid_np at some point that you know the thread to be alive,
and then call kill/tgkill directly. That's still not completely safe
because if you're too late, the tid may have been reused, but then your
code is inherently unsafe anyway.
If we find too much code is still broken, we can come back and disable
the global thread list lookups for anything targeting >= O and then have
another go at really removing this in P...
Bug: http://b/19636317
Test: N6P boots, bionic tests pass
Change-Id: Ia92641212f509344b99ee2a9bfab5383147fcba6
As glibc/netbsd don't protect access to thread struct members by a global
lock, we don't want to do it either. This change reduces the
responsibility of g_thread_list_lock to only protect g_thread_list.
Bug: 19636317
Change-Id: I897890710653dac165d8fa4452c7ecf74abdbf2b
The errors are introduced in "Make pthread join_state not protected by g_thread_list_lock".
Bug: 19636317
Change-Id: I58ae9711da94bfbac809abfd81311eeb70301a4b
1. Move the representation of thread join_state from pthread.attr.flag
to pthread.join_state. This clarifies thread state change.
2. Use atomic operations for pthread.join_state. So we don't need to
protect it by g_thread_list_lock. g_thread_list_lock will be reduced
to only protect g_thread_list or even removed in further changes.
Bug: 19636317
Change-Id: I31fb143a7c69508c7287307dd3b0776993ec0f43
If pthread_detach() is called while the thread is in pthread_exit(),
it takes the risk that no one can free the pthread_internal_t.
So I add PTHREAD_ATTR_FLAG_ZOMBIE to detect this, maybe very rare, but
both glibc and netbsd libpthread have similar function.
Change-Id: Iaa15f651903b8ca07aaa7bd4de46ff14a2f93835
Removed 'join_count' from pthread_internal_t and switched to using the flag
PTHREAD_ATTR_FLAG_JOINED to indicate if a thread is being joined. Combined with
a switch to a while loop in pthread_join, this fixes spurious wake-ups but
prevents a thread from being joined multiple times. This is fine for
two reasons:
1) The pthread_join specification allows for undefined behavior when multiple
threads try to join a single thread.
2) There is no thread safe way to allow multiple threads to join a single
thread with the pthread interface. The second thread calling pthread_join
could be pre-empted until the thread is destroyed and its handle reused for
a different thread. Therefore multi-join is always an error.
Bug: https://code.google.com/p/android/issues/detail?id=52255
Change-Id: I8b6784d47620ffdcdbfb14524e7402e21d46c5f7
imgtec pointed out that pthread_kill(3) was broken, but most of the
other functions that ought to return ESRCH for invalid/exited threads
were equally broken.
Change-Id: I96347f6195549aee0c72dc39063e6c5d06d2e01f
