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Subject[PATCH 18/28] powerpc,kgdb: Introduce low level trap catching
Date
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>
---
arch/powerpc/kernel/kgdb.c | 6 ++++--
arch/powerpc/kernel/traps.c | 7 +++++--
2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index 7aafcc5..8ee7b6e 100644
--- 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 d069ff8..9b72f08 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -809,12 +809,15 @@ 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) {
--
1.6.4.rc1


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