From 5c06743c8a6f2184fbd3792b13dffa30f473b7b7 Mon Sep 17 00:00:00 2001
From: Richard Braun <rbraun@sceen.net>
Date: Mon, 21 Dec 2020 02:10:16 +0100
Subject: [PATCH] Hurd: make sigstates hold a reference on thread ports

This change is required in order to correctly release per-thread
resources. Directly reusing the threading library reference isn't
possible since the sigstate is also used early in the main thread,
before threading is initialized.

* hurd/hurd/signal.h (_hurd_self_sigstate): Drop thread reference after
calling _hurd_thread_sigstate.
(_hurd_critical_section_lock): Likewise.
* hurd/hurdsig.c (_hurd_thread_sigstate): Add a reference on the thread.
(_hurd_sigstate_delete): Drop thread reference.
---
 hurd/hurd/signal.h | 19 +++++++++++++++----
 hurd/hurdsig.c     | 17 ++++++++++++++---
 2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/hurd/hurd/signal.h b/hurd/hurd/signal.h
index f6f91218db..2a0aa20b72 100644
--- a/hurd/hurd/signal.h
+++ b/hurd/hurd/signal.h
@@ -67,7 +67,9 @@ struct hurd_sigstate
 
     spin_lock_t lock;		/* Locks most of the rest of the structure.  */
 
+    /* The signal state holds a reference on the thread port.  */
     thread_t thread;
+
     struct hurd_sigstate *next; /* Linked-list of thread sigstates.  */
 
     sigset_t blocked;		/* What signals are blocked.  */
@@ -119,7 +121,9 @@ struct hurd_sigstate
 
 extern struct hurd_sigstate *_hurd_sigstates;
 
-/* Get the sigstate of a given thread, taking its lock.  */
+/* Get the sigstate of a given thread.  If there was no sigstate for
+   the thread, one is created, and the thread gains a reference.  If
+   the given thread is MACH_PORT_NULL, return the global sigstate.  */
 
 extern struct hurd_sigstate *_hurd_thread_sigstate (thread_t);
 
@@ -162,7 +166,11 @@ _HURD_SIGNAL_H_EXTERN_INLINE struct hurd_sigstate *
 _hurd_self_sigstate (void)
 {
   if (THREAD_GETMEM (THREAD_SELF, _hurd_sigstate) == NULL)
-    THREAD_SETMEM (THREAD_SELF, _hurd_sigstate, _hurd_thread_sigstate (__mach_thread_self ()));
+    {
+      thread_t self = __mach_thread_self ();
+      THREAD_SETMEM (THREAD_SELF, _hurd_sigstate, _hurd_thread_sigstate (self));
+      __mach_port_deallocate (__mach_task_self (), self);
+    }
   return THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
 }
 # endif
@@ -210,12 +218,15 @@ _hurd_critical_section_lock (void)
   ss = THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
   if (ss == NULL)
     {
+      thread_t self = __mach_thread_self ();
+
       /* The thread variable is unset; this must be the first time we've
 	 asked for it.  In this case, the critical section flag cannot
 	 possible already be set.  Look up our sigstate structure the slow
 	 way.  */
-      ss = _hurd_thread_sigstate (__mach_thread_self ());
-      THREAD_SETMEM(THREAD_SELF, _hurd_sigstate, ss);
+      ss = _hurd_thread_sigstate (self);
+      THREAD_SETMEM (THREAD_SELF, _hurd_sigstate, ss);
+      __mach_port_deallocate (__mach_task_self (), self);
     }
 
   if (! __spin_try_lock (&ss->critical_section_lock))
diff --git a/hurd/hurdsig.c b/hurd/hurdsig.c
index 852ae7e441..6fdbf383ee 100644
--- a/hurd/hurdsig.c
+++ b/hurd/hurdsig.c
@@ -114,6 +114,8 @@ _hurd_thread_sigstate (thread_t thread)
 	}
       else
 	{
+	  error_t err;
+
 	  /* Use the global actions as a default for new threads.  */
 	  struct hurd_sigstate *s = _hurd_global_sigstate;
 	  if (s)
@@ -127,6 +129,11 @@ _hurd_thread_sigstate (thread_t thread)
 
 	  ss->next = _hurd_sigstates;
 	  _hurd_sigstates = ss;
+
+	  err = __mach_port_mod_refs (__mach_task_self (), thread,
+				      MACH_PORT_RIGHT_SEND, 1);
+	  if (err)
+	    __libc_fatal ("hurd: Can't add reference on Mach thread\n");
 	}
     }
   __mutex_unlock (&_hurd_siglock);
@@ -135,8 +142,7 @@ _hurd_thread_sigstate (thread_t thread)
 libc_hidden_def (_hurd_thread_sigstate)
 
 /* Destroy a sigstate structure.  Called by libpthread just before the
- * corresponding thread is terminated (the kernel thread port must remain valid
- * until this function is called.) */
+ * corresponding thread is terminated.  */
 void
 _hurd_sigstate_delete (thread_t thread)
 {
@@ -153,7 +159,12 @@ _hurd_sigstate_delete (thread_t thread)
 
   __mutex_unlock (&_hurd_siglock);
   if (ss)
-    free (ss);
+    {
+      if (ss->thread != MACH_PORT_NULL)
+	__mach_port_deallocate (__mach_task_self (), ss->thread);
+
+      free (ss);
+    }
 }
 
 /* Make SS a global receiver, with pthread signal semantics.  */