kgdb: Remove kgdb_schedule_breakpoint()

To the very best of my knowledge there has never been any in-tree
code that calls this function. It exists largely to support an
out-of-tree driver that provides kgdb-over-ethernet using the
netpoll API.

kgdboe has been out-of-tree for more than 10 years and I don't
recall any serious attempt to upstream it at any point in the last
five. At this stage it looks better to stop carrying this code in
the kernel and integrate the code into the out-of-tree driver
instead.

The long term trajectory for the kernel looks likely to include
effort to remove or reduce the use of tasklets (something that has
also been true for the last 10 years). Thus the main real reason
for this patch is to make explicit that the in-tree kgdb features
do not require tasklets.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20210210142525.2876648-1-daniel.thompson@linaro.org
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Jason Wessel <jason.wessel@windriver.com>

include/linux/kgdb.h

@@ -325,7 +325,6 @@ extern char *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_has_hit_break(unsigned long addr);
 
 extern int

kernel/debug/debug_core.c

@@ -119,7 +119,6 @@ static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
  */
 static atomic_t			masters_in_kgdb;
 static atomic_t			slaves_in_kgdb;
-static atomic_t			kgdb_break_tasklet_var;
 atomic_t			kgdb_setting_breakpoint;
 
 struct task_struct		*kgdb_usethread;
@@ -1084,31 +1083,6 @@ 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_OLD(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt);
-
-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);
-
 /**
  *	kgdb_register_io_module - register KGDB IO module
  *	@new_dbg_io_ops: the io ops vector