powerpc,kgdb: Introduce low level trap catching

The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a recursive fault is
to allow the kernel debugger to handle the exception first in
program_check_exception().

The other change here is to make sure that kgdb_handle_exception() is
called with correct parameters when catching an oops, because kdb
needs to know if the entry was an oops, single step, or breakpoint
exception.

[benh@kernel.crashing.org: move debugger_bpt instead of #ifdef]

CC: Paul Mackerras <paulus@samba.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index c81e3de..82a7b22 100644 (file)
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -20,6 +20,7 @@
 #include <linux/smp.h>
 #include <linux/signal.h>
 #include <linux/ptrace.h>
+#include <linux/kdebug.h>
 #include <asm/current.h>
 #include <asm/processor.h>
 #include <asm/machdep.h>
@@ -115,7 +116,8 @@ void kgdb_roundup_cpus(unsigned long flags)
 /* KGDB functions to use existing PowerPC64 hooks. */
 static int kgdb_debugger(struct pt_regs *regs)
 {
-       return kgdb_handle_exception(0, computeSignal(TRAP(regs)), 0, regs);
+       return !kgdb_handle_exception(1, computeSignal(TRAP(regs)),
+                                     DIE_OOPS, regs);
 }
 
 static int kgdb_handle_breakpoint(struct pt_regs *regs)
@@ -123,7 +125,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
        if (user_mode(regs))
                return 0;
 
-       if (kgdb_handle_exception(0, SIGTRAP, 0, regs) != 0)
+       if (kgdb_handle_exception(1, SIGTRAP, 0, regs) != 0)
                return 0;
 
        if (*(u32 *) (regs->nip) == *(u32 *) (&arch_kgdb_ops.gdb_bpt_instr))

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 29d128e..b6859aa 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -815,12 +815,15 @@ void __kprobes program_check_exception(struct pt_regs *regs)
                return;
        }
        if (reason & REASON_TRAP) {
+               /* Debugger is first in line to stop recursive faults in
+                * rcu_lock, notify_die, or atomic_notifier_call_chain */
+               if (debugger_bpt(regs))
+                       return;
+
                /* trap exception */
                if (notify_die(DIE_BPT, "breakpoint", regs, 5, 5, SIGTRAP)
                                == NOTIFY_STOP)
                        return;
-               if (debugger_bpt(regs))
-                       return;
 
                if (!(regs->msr & MSR_PR) &&  /* not user-mode */
                    report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) {