[scudo][standalone] Fork support

Summary:
fork() wasn't well (or at all) supported in Scudo. This materialized
in deadlocks in children.

In order to properly support fork, we will lock the allocator pre-fork
and unlock it post-fork in parent and child. This is done via a
`pthread_atfork` call installing the necessary handlers.

A couple of things suck here: this function allocates - so this has to
be done post initialization as our init path is not reentrance, and it
doesn't allow for an extra pointer - so we can't pass the allocator we
are currently working with.

In order to work around this, I added a post-init template parameter
that gets executed once the allocator is initialized for the current
thread. Its job for the C wrappers is to install the atfork handlers.

I reorganized a bit the impacted area and added some tests, courtesy
of cferris@ that were deadlocking prior to this fix.

Subscribers: jfb, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D72470

1 files changed, 3 insertions, 2 deletions

diff --git a/compiler-rt/lib/scudo/standalone/tsd_exclusive.h b/compiler-rt/lib/scudo/standalone/tsd_exclusive.h
index 89b001a739c..69479ea7bdf 100644
--- a/compiler-rt/lib/scudo/standalone/tsd_exclusive.h
+++ b/compiler-rt/lib/scudo/standalone/tsd_exclusive.h
@@ -11,8 +11,6 @@
 
 #include "tsd.h"
 
-#include <pthread.h>
-
 namespace scudo {
 
 enum class ThreadState : u8 {
@@ -62,6 +60,7 @@ template <class Allocator> struct TSDRegistryExT {
   // To disable the exclusive TSD registry, we effectively lock the fallback TSD
   // and force all threads to attempt to use it instead of their local one.
   void disable() {
+    Mutex.lock();
     FallbackTSD->lock();
     atomic_store(&Disabled, 1U, memory_order_release);
   }
@@ -69,6 +68,7 @@ template <class Allocator> struct TSDRegistryExT {
   void enable() {
     atomic_store(&Disabled, 0U, memory_order_release);
     FallbackTSD->unlock();
+    Mutex.unlock();
   }
 
 private:
@@ -90,6 +90,7 @@ private:
         pthread_setspecific(PThreadKey, reinterpret_cast<void *>(Instance)), 0);
     ThreadTSD.initLinkerInitialized(Instance);
     State = ThreadState::Initialized;
+    Instance->callPostInitCallback();
   }
 
   pthread_key_t PThreadKey;