From 4f4738427dd8b673ec46ffb2b31e708aca4daa35 Mon Sep 17 00:00:00 2001
From: Martin Stein <martin.stein@genode-labs.com>
Date: Wed, 18 Sep 2013 12:57:01 +0200
Subject: [PATCH] hw: release pagers from faulting threads

ref #589
---
 base-hw/include/kernel/syscalls.h   | 19 ++++++++-----------
 base-hw/src/core/kernel.cc          | 23 ++++++++++++++---------
 base-hw/src/core/platform_thread.cc | 13 ++++++++-----
 3 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/base-hw/include/kernel/syscalls.h b/base-hw/include/kernel/syscalls.h
index 928279a2c1..123da1bc8b 100644
--- a/base-hw/include/kernel/syscalls.h
+++ b/base-hw/include/kernel/syscalls.h
@@ -351,21 +351,18 @@ namespace Kernel
 
 
 	/**
-	 * Set a thread that gets informed about pagefaults of another thread
+	 * Set or unset an IPC destination for pagefaults reports of a thread
 	 *
-	 * \param pager_id    ID of the thread that shall get informed.
-	 *                    Subsequently this thread gets an IPC message,
-	 *                    wich contains an according 'Pagefault' object for
-	 *                    every pagefault the faulter throws.
-	 * \param faulter_id  ID of the thread that throws the pagefaults
-	 *                    wich shall be notified. After every pagefault this
-	 *                    thread remains paused to be reactivated by
-	 *                    'resume_thread'.
+	 * \param pager_id    kernel name of the pager thread or 0 for "unset"
+	 * \param faulter_id  kernel name of the thread that throws the pagefaults
 	 *
 	 * Restricted to core threads.
 	 */
-	inline void set_pager(unsigned const pager_id, unsigned const faulter_id) {
-		syscall(SET_PAGER, pager_id, faulter_id); }
+	inline void set_pager(unsigned const pager_id, unsigned const faulter_id)
+	{
+		syscall(SET_PAGER, pager_id, faulter_id);
+	}
+
 
 	/**
 	 * Print a char 'c' to the kernels serial ouput
diff --git a/base-hw/src/core/kernel.cc b/base-hw/src/core/kernel.cc
index 9a3a10c66b..5be3915ae8 100644
--- a/base-hw/src/core/kernel.cc
+++ b/base-hw/src/core/kernel.cc
@@ -468,16 +468,21 @@ namespace Kernel
 	 */
 	void do_set_pager(Thread * const user)
 	{
-		/* assert preconditions */
-		assert(user->pd_id() == core_id());
-
-		/* get faulter and pager thread */
-		Thread * const p = Thread::pool()->object(user->user_arg_1());
-		Thread * const f = Thread::pool()->object(user->user_arg_2());
-		assert(p && f);
-
+		/* check permissions */
+		if (user->pd_id() != core_id()) {
+			PERR("not entitled to set pager");
+			return;
+		}
+		/* lookup faulter and pager thread */
+		unsigned const pager_id = user->user_arg_1();
+		Thread * const pager    = Thread::pool()->object(pager_id);
+		Thread * const faulter  = Thread::pool()->object(user->user_arg_2());
+		if ((pager_id && !pager) || !faulter) {
+			PERR("failed to set pager");
+			return;
+		}
 		/* assign pager */
-		f->pager(p);
+		faulter->pager(pager);
 	}
 
 
diff --git a/base-hw/src/core/platform_thread.cc b/base-hw/src/core/platform_thread.cc
index a147c4cc42..2750f55e98 100644
--- a/base-hw/src/core/platform_thread.cc
+++ b/base-hw/src/core/platform_thread.cc
@@ -181,11 +181,14 @@ int Platform_thread::start(void * ip, void * sp, unsigned int cpu_no)
 
 void Platform_thread::pager(Pager_object * const pager)
 {
-	/* announce pager thread to kernel */
-	Kernel::set_pager(pager->cap().dst(), _id);
-
-	/* get RM client from pager pointer */
-	_rm_client = dynamic_cast<Rm_client *>(pager);
+	if (pager) {
+		Kernel::set_pager(pager->cap().dst(), _id);
+		_rm_client = dynamic_cast<Rm_client *>(pager);
+		return;
+	}
+	Kernel::set_pager(0, _id);
+	_rm_client = 0;
+	return;
 }