linux-kernel - [PATCH 23/40] kgdb: Add the ability to schedule a breakpoint via a tasklet

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Date:	Thu, 14 Jan 2010 08:59:19 -0600
From:	Jason Wessel <jason.wessel@...driver.com>
To:	linux-kernel@...r.kernel.org
Cc:	kgdb-bugreport@...ts.sourceforge.net, mingo@...e.hu,
	Jason Wessel <jason.wessel@...driver.com>
Subject: [PATCH 23/40] kgdb: Add the ability to schedule a breakpoint via a tasklet

Some kgdb I/O modules require the ability to create a breakpoint
tasklet, such as kgdboc and external modules such as kgdboe.  The
breakpoint tasklet is used as an asynchronous entry point into the
debugger which will have a different function scope than the current
execution path where it might not be safe to have an inline
breakpoint.  This is true of some of the kgdb I/O drivers which share
code with kgdb and rest of the kernel users.

Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
---
 include/linux/kgdb.h      |    1 +
 kernel/debug/debug_core.c |   26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e4e9206..076f3c6 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -270,6 +270,7 @@ extern int kgdb_mem2hex(char *mem, char *buf, int count);
 extern int kgdb_hex2mem(char *buf, char *mem, int count);
 
 extern int kgdb_isremovedbreak(unsigned long addr);
+extern void kgdb_schedule_breakpoint(void);
 
 extern int
 kgdb_handle_exception(int ex_vector, int signo, int err_code,
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 5ceaa0f..e02c552 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -112,6 +112,7 @@ atomic_t			kgdb_active = ATOMIC_INIT(-1);
  */
 static atomic_t			passive_cpu_wait[NR_CPUS];
 static atomic_t			cpu_in_kgdb[NR_CPUS];
+static atomic_t			kgdb_break_tasklet_var;
 atomic_t			kgdb_setting_breakpoint;
 
 struct task_struct		*kgdb_usethread;
@@ -776,6 +777,31 @@ static void kgdb_unregister_callbacks(void)
 	}
 }
 
+/*
+ * There are times a tasklet needs to be used vs a compiled in
+ * break point so as to cause an exception outside a kgdb I/O module,
+ * such as is the case with kgdboe, where calling a breakpoint in the
+ * I/O driver itself would be fatal.
+ */
+static void kgdb_tasklet_bpt(unsigned long ing)
+{
+	kgdb_breakpoint();
+	atomic_set(&kgdb_break_tasklet_var, 0);
+}
+
+static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
+
+void kgdb_schedule_breakpoint(void)
+{
+	if (atomic_read(&kgdb_break_tasklet_var) ||
+		atomic_read(&kgdb_active) != -1 ||
+		atomic_read(&kgdb_setting_breakpoint))
+		return;
+	atomic_inc(&kgdb_break_tasklet_var);
+	tasklet_schedule(&kgdb_tasklet_breakpoint);
+}
+EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
+
 static void kgdb_initial_breakpoint(void)
 {
 	kgdb_break_asap = 0;
-- 
1.6.3.1.9.g95405b

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