From: Waldemar Kozaczuk <jwkozac...@gmail.com>
Committer: Nadav Har'El <n...@scylladb.com>
Branch: master
thread: make walking parent-child thread relationship safer
This patch replaces _parent_link/thread_list with a simple parent_thread_id
field to make walking parent-child list safer in elf::visible() method.
Signed-off-by: Waldemar Kozaczuk <jwkozac...@gmail.com>
Message-Id: <20200112224434.13489-1-jwkozac...@gmail.com>
---
diff --git a/core/elf.cc b/core/elf.cc
--- a/core/elf.cc
+++ b/core/elf.cc
@@ -151,17 +151,29 @@ bool object::visible(void) const
return true;
}
+ auto current_thread = sched::thread::current();
if (level == VisibilityLevel::ThreadOnly) {
- return thread == sched::thread::current();
+ return thread == current_thread;
}
- // Is current thread the same as "thread" or is it a child ?`
- for (auto t = sched::thread::current(); t != nullptr; t = t->parent())
{
- if (t == thread) {
- return true;
- }
+ // Is current thread the same as "thread" or is it a child of it?
+ if (thread == current_thread) {
+ return true;
}
- return false;
+
+ bool visible = false;
+ auto next_parent_id = current_thread->parent_id();
+ while (next_parent_id) {
+ sched::with_thread_by_id(next_parent_id, [&next_parent_id,
&visible, thread] (sched::thread *t) {
+ if (t == thread) {
+ visible = true;
+ next_parent_id = 0;
+ } else {
+ next_parent_id = t ? t->parent_id() : 0;
+ }
+ });
+ }
+ return visible;
}
void object::set_visibility(elf::VisibilityLevel visibilityLevel)
@@ -171,7 +183,6 @@ void object::set_visibility(elf::VisibilityLevel
visibilityLevel)
_visibility_level.store(visibilityLevel, std::memory_order_release);
}
-
template <>
void* object::lookup(const char* symbol)
{
diff --git a/core/sched.cc b/core/sched.cc
--- a/core/sched.cc
+++ b/core/sched.cc
@@ -1002,11 +1002,7 @@ thread::thread(std::function<void ()> func, attr
attr, bool main, bool app)
sizeof(_attr._name) - 1);
}
- // Note that we never delete _parent_link. This is intentional as it
lets us track
- // parent-child relationship safely even when given thread is
destroyed.
- _parent_link = new thread_list();
- _parent_link->_self.store(this);
- _parent_link->_parent = (s_current && !main) ?
s_current->_parent_link : nullptr;
+ _parent_id = s_current ? s_current->id() : 0;
}
static std::list<std::function<void ()>> exit_notifiers
@@ -1044,8 +1040,6 @@ thread::~thread()
{
cancel_this_thread_alarm();
- _parent_link->_self.store(nullptr, std::memory_order_release);
-
if (!_attr._detached) {
join();
}
diff --git a/include/osv/sched.hh b/include/osv/sched.hh
--- a/include/osv/sched.hh
+++ b/include/osv/sched.hh
@@ -364,13 +364,6 @@ public:
return *this;
}
};
- // Simple single-linked list that allows to keep track of
- // "parent-child" relationship between threads. The "parent" is
- // the thread that constructs given "child" thread
- struct thread_list {
- std::atomic<thread*> _self;
- thread_list *_parent;
- };
private:
// Unlike the detached user visible attribute, those are internal to
@@ -640,7 +633,10 @@ public:
{
return static_cast<T*>(do_remote_thread_local_var(var));
}
- thread *parent();
+ unsigned int parent_id() const
+ {
+ return _parent_id;
+ }
private:
virtual void timer_fired() override;
struct detached_state;
@@ -777,7 +773,7 @@ private:
inline void cputime_estimator_get(
osv::clock::uptime::time_point &running_since,
osv::clock::uptime::duration &total_cpu_time);
- thread_list *_parent_link;
+ unsigned int _parent_id;
};
class thread_handle {
@@ -1304,12 +1300,6 @@ inline thread_handle thread::handle()
return thread_handle(*this);
}
-inline thread* thread::parent()
-{
- auto _parent = _parent_link->_parent;
- return _parent ? _parent->_self.load(std::memory_order_acquire) :
nullptr;
-}
-
inline void* thread::get_tls(ulong module)
{
if (module >= _tls.size()) {
--
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