hw: don't take the log backend's mutex in kernel

To prevent the kernel to deadlock, or call itself with a syscall when
using a lock potentially hold by a core thread, the log console's
backend for core (hw) gets replaced by a specific variant that checks
whether it runs in the kernel context before using the mutex.

Fix genodelabs/genode#3280

repos/base-hw/lib/mk/base-hw-common.mk

@@ -10,3 +10,8 @@ include $(BASE_DIR)/lib/mk/base-common.inc
 SRC_CC += rpc_dispatch_loop.cc
 SRC_CC += thread.cc thread_myself.cc thread_bootstrap.cc
 SRC_CC += signal_transmitter.cc
+
+# filter out log.cc from the generic base library
+# in core and hw kernel we have to implement it differently
+SRC_CC_WITH_LOG_CC := $(SRC_CC)
+SRC_CC = $(filter-out log.cc,$(SRC_CC_WITH_LOG_CC))

repos/base-hw/lib/mk/base-hw.mk

@@ -1,5 +1,6 @@
 include $(BASE_DIR)/lib/mk/base.inc
 
+SRC_CC += log.cc
 SRC_CC += thread_start.cc
 SRC_CC += capability.cc
 SRC_CC += cache.cc

repos/base-hw/src/core/core_log_out.cc

@@ -12,15 +12,22 @@
  * under the terms of the GNU Affero General Public License version 3.
  */
 
+/* Genode includes */
+#include <base/log.h>
+#include <base/thread.h>
+
 /* base-internal includes */
 #include <base/internal/output.h>
 #include <base/internal/raw_write_string.h>
 
 #include <core_log.h>
+#include <kernel/cpu.h>
 #include <kernel/log.h>
 
+using namespace Genode;
 
-void Genode::Core_log::out(char const c) { Kernel::log(c); }
+
+void Core_log::out(char const c) { Kernel::log(c); }
 
 
 void Genode::raw_write_string(char const *str)
@@ -28,3 +35,75 @@ void Genode::raw_write_string(char const *str)
 	while (char c = *str++)
 		Kernel::log(c);
 }
+
+
+/************************************************************
+ ** Utility to check whether kernel or core code is active **
+ ************************************************************/
+
+extern void const * const kernel_stack;
+
+static inline bool running_in_kernel()
+{
+	addr_t const stack_base = reinterpret_cast<addr_t>(&kernel_stack);
+	static constexpr size_t stack_size =
+		NR_OF_CPUS * Kernel::Cpu::KERNEL_STACK_SIZE;
+
+	/* check stack variable against kernel stack area */
+	return ((addr_t)&stack_base) >= stack_base &&
+	       ((addr_t)&stack_base) < (stack_base + stack_size);
+}
+
+
+/*******************************************
+ ** Implementation of src/lib/base/log.cc **
+ *******************************************/
+
+void Log::_acquire(Type type)
+{
+	if (!running_in_kernel()) _mutex.acquire();
+
+	/*
+	 * Mark warnings and errors via distinct colors.
+	 */
+	switch (type) {
+	case LOG:                                              break;
+	case WARNING: _output.out_string("\033[34mWarning: "); break;
+	case ERROR:   _output.out_string("\033[31mError: ");   break;
+	};
+}
+
+
+void Log::_release()
+{
+	/*
+	 * Reset color and add newline
+	 */
+	_output.out_string("\033[0m\n");
+
+	if (!running_in_kernel()) _mutex.release();
+}
+
+
+void Raw::_acquire()
+{
+	/*
+	 * Mark raw output with distinct color
+	 */
+	_output().out_string("\033[32mKernel: ");
+}
+
+
+void Raw::_release()
+{
+	/*
+	 * Reset color and add newline
+	 */
+	_output().out_string("\033[0m\n");
+}
+
+
+void Trace_output::Write_trace_fn::operator () (char const *s)
+{
+	Thread::trace(s);
+}