kgdb,x86: fix regression in detach handling

The fix from ba773f7c510c0b252145933926c636c439889207
(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>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index ec592caac4b4..cd21b654dec6 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/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;
         }
 }