kgdb,x86: fix regression in detach handling

The fix from ba773f7c
(x86,kgdb: Fix hw breakpoint regression) was not entirely complete.

The kgdb_remove_all_hw_break() function also needs to call the
hw_break_release_slot() or else a breakpoint can get activated again
after the debugger has detached.

The kgdb test suite exposes the behavior in the form of either a hang
or repetitive failure.  The kernel config that exposes the problem
contains all of the following:

CONFIG_DEBUG_RODATA=y
CONFIG_KGDB_TESTS=y
CONFIG_KGDB_TESTS_ON_BOOT=y
CONFIG_KGDB_TESTS_BOOT_STRING="V1F100"
Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Tested-by: Frederic Weisbecker <fweisbec@gmail.com>

arch/x86/kernel/kgdb.c

@@ -315,14 +315,18 @@ static void kgdb_remove_all_hw_break(void)
 		if (!breakinfo[i].enabled)
 			continue;
 		bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
-		if (bp->attr.disabled == 1)
+		if (!bp->attr.disabled) {
+			arch_uninstall_hw_breakpoint(bp);
+			bp->attr.disabled = 1;
 			continue;
+		}
 		if (dbg_is_early)
 			early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
 						 breakinfo[i].type);
-		else
-			arch_uninstall_hw_breakpoint(bp);
-		bp->attr.disabled = 1;
+		else if (hw_break_release_slot(i))
+			printk(KERN_ERR "KGDB: hw bpt remove failed %lx\n",
+			       breakinfo[i].addr);
+		breakinfo[i].enabled = 0;
 	}
 }