Fix fork/spawn race conditions

src/fbsd_wrapper.cc

@@ -6,6 +6,7 @@
 #include <errno.h>
 #include <malloc.h>
 #include <pthread.h>
+#include <spawn.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -57,6 +58,9 @@
 #define WEAK_REDEF3(type, fname, arg1, arg2, arg3) \
   MESH_EXPORT type fname(arg1, arg2, arg3)         \
   __THROW WEAK(mesh_##fname)
+#define WEAK_REDEF6(type, fname, arg1, arg2, arg3, arg4, arg5, arg6) \
+  MESH_EXPORT type fname(arg1, arg2, arg3, arg4, arg5, arg6)         \
+  __THROW WEAK(mesh_##fname)
 
 extern "C" {
 WEAK_REDEF1(void *, malloc, size_t);
@@ -69,6 +73,10 @@ WEAK_REDEF2(void *, memalign, size_t, size_t);
 WEAK_REDEF3(int, posix_memalign, void **, size_t, size_t);
 WEAK_REDEF2(void *, aligned_alloc, size_t, size_t);
 WEAK_REDEF1(size_t, malloc_usable_size, const void *);
+WEAK_REDEF6(int, posix_spawn, pid_t *, const char *, const posix_spawn_file_actions_t *, const posix_spawnattr_t *,
+            char *const[], char *const[]);
+WEAK_REDEF6(int, posix_spawnp, pid_t *, const char *, const posix_spawn_file_actions_t *, const posix_spawnattr_t *,
+            char *const[], char *const[]);
 }
 
 #include "wrapper.cc"

src/gnu_wrapper.cc

@@ -10,6 +10,7 @@
 #include <errno.h>
 #include <malloc.h>
 #include <pthread.h>
+#include <spawn.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -61,6 +62,9 @@
 #define WEAK_REDEF3(type, fname, arg1, arg2, arg3) \
   MESH_EXPORT type fname(arg1, arg2, arg3)         \
   __THROW WEAK(mesh_##fname)
+#define WEAK_REDEF6(type, fname, arg1, arg2, arg3, arg4, arg5, arg6) \
+  MESH_EXPORT type fname(arg1, arg2, arg3, arg4, arg5, arg6)         \
+  __THROW WEAK(mesh_##fname)
 
 extern "C" {
 WEAK_REDEF1(void *, malloc, size_t);
@@ -72,6 +76,10 @@ WEAK_REDEF2(void *, memalign, size_t, size_t);
 WEAK_REDEF3(int, posix_memalign, void **, size_t, size_t);
 WEAK_REDEF2(void *, aligned_alloc, size_t, size_t);
 WEAK_REDEF1(size_t, malloc_usable_size, void *);
+WEAK_REDEF6(int, posix_spawn, pid_t *, const char *, const posix_spawn_file_actions_t *, const posix_spawnattr_t *,
+            char *const[], char *const[]);
+WEAK_REDEF6(int, posix_spawnp, pid_t *, const char *, const posix_spawn_file_actions_t *, const posix_spawnattr_t *,
+            char *const[], char *const[]);
 }
 
 #include "wrapper.cc"

src/libmesh.cc

@@ -442,7 +442,54 @@ ssize_t MESH_EXPORT recvmsg(int sockfd, struct msghdr *msg, int flags) {
   return mesh::dispatchByPageSize([=](auto &rt) { return rt.recvmsg(sockfd, msg, flags); });
 }
 #endif
+}  // extern "C"
+
+namespace {
+// RAII guard for the three locks needed during spawn operations.
+// Acquires locks in the same order as prepareForFork to prevent races.
+template <size_t PageSize>
+class SpawnLockGuard {
+public:
+  SpawnLockGuard() {
+    mesh::runtime<PageSize>().heap().lock();
+    mesh::runtime<PageSize>().lock();
+    mesh::internal::Heap().lock();
+  }
+
+  ~SpawnLockGuard() {
+    mesh::internal::Heap().unlock();
+    mesh::runtime<PageSize>().unlock();
+    mesh::runtime<PageSize>().heap().unlock();
+  }
+
+  SpawnLockGuard(const SpawnLockGuard &) = delete;
+  SpawnLockGuard &operator=(const SpawnLockGuard &) = delete;
+};
+}  // namespace
+
+extern "C" {
+int MESH_EXPORT mesh_posix_spawn(pid_t *pid, const char *path, const posix_spawn_file_actions_t *file_actions,
+                                 const posix_spawnattr_t *attrp, char *const argv[], char *const envp[]) {
+  if (likely(getPageSize() == kPageSize4K)) {
+    SpawnLockGuard<kPageSize4K> guard;
+    return mesh::real::posix_spawn(pid, path, file_actions, attrp, argv, envp);
+  } else {
+    SpawnLockGuard<kPageSize16K> guard;
+    return mesh::real::posix_spawn(pid, path, file_actions, attrp, argv, envp);
+  }
+}
+
+int MESH_EXPORT mesh_posix_spawnp(pid_t *pid, const char *file, const posix_spawn_file_actions_t *file_actions,
+                                  const posix_spawnattr_t *attrp, char *const argv[], char *const envp[]) {
+  if (likely(getPageSize() == kPageSize4K)) {
+    SpawnLockGuard<kPageSize4K> guard;
+    return mesh::real::posix_spawnp(pid, file, file_actions, attrp, argv, envp);
+  } else {
+    SpawnLockGuard<kPageSize16K> guard;
+    return mesh::real::posix_spawnp(pid, file, file_actions, attrp, argv, envp);
+  }
 }
+}  // extern "C"
 
 #if defined(__linux__)
 #include "gnu_wrapper.cc"

src/meshable_arena.cc

@@ -18,9 +18,6 @@ void MeshableArena<PageSize>::prepareForFork() {
   runtime<PageSize>().lock();
   internal::Heap().lock();
 
-  int r = mprotect(_arenaBegin, kArenaSize, PROT_READ);
-  hard_assert(r == 0);
-
   int err = pipe(_forkPipe);
   if (err == -1) {
     abort();
@@ -49,9 +46,6 @@ void MeshableArena<PageSize>::afterForkParent() {
   _forkPipe[0] = -1;
   _forkPipe[1] = -1;
 
-  int r = mprotect(_arenaBegin, kArenaSize, PROT_READ | PROT_WRITE);
-  hard_assert(r == 0);
-
   runtime<PageSize>().unlock();
   runtime<PageSize>().heap().unlock();
 }
@@ -96,9 +90,6 @@ void MeshableArena<PageSize>::afterForkChild() {
     d_assert(result == CPUInfo::PageSize);
   }
 
-  int r = mprotect(_arenaBegin, kArenaSize, PROT_READ | PROT_WRITE);
-  hard_assert(r == 0);
-
   void *ptr = mmap(_arenaBegin, kArenaSize, HL_MMAP_PROTECTION_MASK, kMapShared | MAP_FIXED, newFd, 0);
   hard_assert_msg(ptr != MAP_FAILED, "map failed: %d", errno);
 

src/meshable_arena.h

@@ -418,8 +418,6 @@ MeshableArena<PageSize>::MeshableArena() : SuperHeap(), _fastPrng(internal::seed
     madvise(_arenaBegin, kArenaSize, MADV_DONTDUMP);
   }
 
-  debug("MeshableArena(%p): fd:%4d\t%p-%p\n", this, _fd, _arenaBegin, arenaEnd());
-
   atexit(staticAtExit);
   pthread_atfork(staticPrepareForFork, staticAfterForkParent, staticAfterForkChild);
 }

src/real.cc

@@ -31,6 +31,9 @@ DEFINE_REAL(pthread_exit);
 DEFINE_REAL(sigaction);
 DEFINE_REAL(sigprocmask);
 
+DEFINE_REAL(posix_spawn);
+DEFINE_REAL(posix_spawnp);
+
 void init() {
   static mutex initLock;
   static bool initialized;
@@ -51,6 +54,9 @@ void init() {
 
   INIT_REAL(sigaction, RTLD_NEXT);
   INIT_REAL(sigprocmask, RTLD_NEXT);
+
+  INIT_REAL(posix_spawn, RTLD_NEXT);
+  INIT_REAL(posix_spawnp, RTLD_NEXT);
 }
 }  // namespace real
 }  // namespace mesh

src/real.h

@@ -5,6 +5,7 @@
 
 #include <pthread.h>
 #include <signal.h>
+#include <spawn.h>
 
 #ifdef __linux__
 #include <sys/epoll.h>
@@ -34,6 +35,9 @@ DECLARE_REAL(pthread_exit);
 
 DECLARE_REAL(sigaction);
 DECLARE_REAL(sigprocmask);
+
+DECLARE_REAL(posix_spawn);
+DECLARE_REAL(posix_spawnp);
 }  // namespace real
 }  // namespace mesh