Merge tag 'for_linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb

Pull KGDB/KDB updates from Jason Wessel:
 "Fixes:
   - Fix KDB keyboard repeat scan codes and leaked keyboard events
   - Fix kernel crash with kdb_printf() for users who compile new
     kdb_printf()'s in early code
   - Return all segment registers to gdb on x86_64

  Features:
   - KDB/KGDB hook the reboot notifier and end user can control if it
     stops, detaches or does nothing (updated docs as well)
   - Notify users who use CONFIG_DEBUG_RODATA to use hw breakpoints"

* tag 'for_linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
  kdb: Add message about CONFIG_DEBUG_RODATA on failure to install breakpoint
  kdb: Avoid using dbg_io_ops until it is initialized
  kgdb,debug_core: add the ability to control the reboot notifier
  KDB: Fix usability issues relating to the 'enter' key.
  kgdb,debug-core,gdbstub: Hook the reboot notifier for debugger detach
  kgdb: Respect that flush op is optional
  kgdb: x86: Return all segment registers also in 64-bit mode

5 files changed, 91 insertions, 23 deletions

diff --git a/kernel/debug/kdb/kdb_bp.c b/kernel/debug/kdb/kdb_bp.c
index 20059ef4459a..8418c2f8ec5d 100644
--- a/kernel/debug/kdb/kdb_bp.c
+++ b/kernel/debug/kdb/kdb_bp.c
@@ -153,6 +153,13 @@ static int _kdb_bp_install(struct pt_regs *regs, kdb_bp_t *bp)
         } else {
                 kdb_printf("%s: failed to set breakpoint at 0x%lx\n",
                            __func__, bp->bp_addr);
+#ifdef CONFIG_DEBUG_RODATA
+                if (!bp->bp_type) {
+                        kdb_printf("Software breakpoints are unavailable.\n"
+                                   "  Change the kernel CONFIG_DEBUG_RODATA=n\n"
+                                   "  OR use hw breaks: help bph\n");
+                }
+#endif
                 return 1;
         }
         return 0;
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 4802eb5840e1..9b5f17da1c56 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -689,7 +689,7 @@ kdb_printit:
         if (!dbg_kdb_mode && kgdb_connected) {
                 gdbstub_msg_write(kdb_buffer, retlen);
         } else {
-                if (!dbg_io_ops->is_console) {
+                if (dbg_io_ops && !dbg_io_ops->is_console) {
                         len = strlen(kdb_buffer);
                         cp = kdb_buffer;
                         while (len--) {
diff --git a/kernel/debug/kdb/kdb_keyboard.c b/kernel/debug/kdb/kdb_keyboard.c
index 4bca634975c0..118527aa60ea 100644
--- a/kernel/debug/kdb/kdb_keyboard.c
+++ b/kernel/debug/kdb/kdb_keyboard.c
@@ -25,6 +25,7 @@
 #define KBD_STAT_MOUSE_OBF      0x20    /* Mouse output buffer full */
 
 static int kbd_exists;
+static int kbd_last_ret;
 
 /*
  * Check if the keyboard controller has a keypress for us.
@@ -90,8 +91,11 @@ int kdb_get_kbd_char(void)
                 return -1;
         }
 
-        if ((scancode & 0x80) != 0)
+        if ((scancode & 0x80) != 0) {
+                if (scancode == 0x9c)
+                        kbd_last_ret = 0;
                 return -1;
+        }
 
         scancode &= 0x7f;
 
@@ -178,35 +182,82 @@ int kdb_get_kbd_char(void)
                 return -1;      /* ignore unprintables */
         }
 
-        if ((scancode & 0x7f) == 0x1c) {
-                /*
-                 * enter key.  All done.  Absorb the release scancode.
-                 */
+        if (scancode == 0x1c) {
+                kbd_last_ret = 1;
+                return 13;
+        }
+
+        return keychar & 0xff;
+}
+EXPORT_SYMBOL_GPL(kdb_get_kbd_char);
+
+/*
+ * Best effort cleanup of ENTER break codes on leaving KDB. Called on
+ * exiting KDB, when we know we processed an ENTER or KP ENTER scan
+ * code.
+ */
+void kdb_kbd_cleanup_state(void)
+{
+        int scancode, scanstatus;
+
+        /*
+         * Nothing to clean up, since either
+         * ENTER was never pressed, or has already
+         * gotten cleaned up.
+         */
+        if (!kbd_last_ret)
+                return;
+
+        kbd_last_ret = 0;
+        /*
+         * Enter key. Need to absorb the break code here, lest it gets
+         * leaked out if we exit KDB as the result of processing 'g'.
+         *
+         * This has several interesting implications:
+         * + Need to handle KP ENTER, which has break code 0xe0 0x9c.
+         * + Need to handle repeat ENTER and repeat KP ENTER. Repeats
+         *   only get a break code at the end of the repeated
+         *   sequence. This means we can't propagate the repeated key
+         *   press, and must swallow it away.
+         * + Need to handle possible PS/2 mouse input.
+         * + Need to handle mashed keys.
+         */
+
+        while (1) {
                 while ((inb(KBD_STATUS_REG) & KBD_STAT_OBF) == 0)
-                        ;
+                        cpu_relax();
 
                 /*
-                 * Fetch the scancode
+                 * Fetch the scancode.
                  */
                 scancode = inb(KBD_DATA_REG);
                 scanstatus = inb(KBD_STATUS_REG);
 
-                while (scanstatus & KBD_STAT_MOUSE_OBF) {
-                        scancode = inb(KBD_DATA_REG);
-                        scanstatus = inb(KBD_STATUS_REG);
-                }
+                /*
+                 * Skip mouse input.
+                 */
+                if (scanstatus & KBD_STAT_MOUSE_OBF)
+                        continue;
 
-                if (scancode != 0x9c) {
-                        /*
-                         * Wasn't an enter-release,  why not?
-                         */
-                        kdb_printf("kdb: expected enter got 0x%x status 0x%x\n",
-                               scancode, scanstatus);
-                }
+                /*
+                 * If we see 0xe0, this is either a break code for KP
+                 * ENTER, or a repeat make for KP ENTER. Either way,
+                 * since the second byte is equivalent to an ENTER,
+                 * skip the 0xe0 and try again.
+                 *
+                 * If we see 0x1c, this must be a repeat ENTER or KP
+                 * ENTER (and we swallowed 0xe0 before). Try again.
+                 *
+                 * We can also see make and break codes for other keys
+                 * mashed before or after pressing ENTER. Thus, if we
+                 * see anything other than 0x9c, we have to try again.
+                 *
+                 * Note, if you held some key as ENTER was depressed,
+                 * that break code would get leaked out.
+                 */
+                if (scancode != 0x9c)
+                        continue;
 
-                return 13;
+                return;
         }
-
-        return keychar & 0xff;
 }
-EXPORT_SYMBOL_GPL(kdb_get_kbd_char);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index e2ae7349437f..67b847dfa2bb 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1400,6 +1400,9 @@ int kdb_main_loop(kdb_reason_t reason, kdb_reason_t reason2, int error,
         if (KDB_STATE(DOING_SS))
                 KDB_STATE_CLEAR(SSBPT);
 
+        /* Clean up any keyboard devices before leaving */
+        kdb_kbd_cleanup_state();
+
         return result;
 }
 
diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index e381d105b40b..47c4e56e513b 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -246,6 +246,13 @@ extern void debug_kusage(void);
 
 extern void kdb_set_current_task(struct task_struct *);
 extern struct task_struct *kdb_current_task;
+
+#ifdef CONFIG_KDB_KEYBOARD
+extern void kdb_kbd_cleanup_state(void);
+#else /* ! CONFIG_KDB_KEYBOARD */
+#define kdb_kbd_cleanup_state()
+#endif /* ! CONFIG_KDB_KEYBOARD */
+
 #ifdef CONFIG_MODULES
 extern struct list_head *kdb_modules;
 #endif /* CONFIG_MODULES */