[Kprobe][PATCH 1/1] ia64: Fix Kprobes reentrancy

["Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>]

From "Anil S Keshvamurthy@intel.com" <anil.s.keshavamurthy@intel.com>

Subject:[Kprobe] Fix kprobe reentracy 

In case of reentrance i.e when a probe handler calls a functions
which inturn has a probe, we save a previous kprobe information
and just single step the reentrant probe without calling the
actual probe handler. During this reentracy period, if an interrupt
occurs and if probe happens to trigger in the inturrupt path, then 
we were corrupting the previous kprobe( as we were overriding
the previous kprobe info) info their by crashing the
system. This patch fixes this issues by having a an array of
previous kprobe info struct(with the array size of 2).

This similar technique is not needed on i386 and x86_64 because
by default interrupts are turn off in the break/int3 exception
handler.

Signed-off-by: "Anil S Keshavamurthy" <anil.s.keshavamurthy@intel.com"

---
 arch/ia64/kernel/kprobes.c |   12 ++++++++----
 include/asm-ia64/kprobes.h |    4 +++-
 2 files changed, 11 insertions(+), 5 deletions(-)

Index: work/arch/ia64/kernel/kprobes.c
=================================--- work.orig/arch/ia64/kernel/kprobes.c	2007-02-04 10:44:54.000000000 -0800
+++ work/arch/ia64/kernel/kprobes.c	2007-05-08 13:47:34.000000000 -0700
@@ -370,14 +370,18 @@
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
-	kcb->prev_kprobe.kp = kprobe_running();
-	kcb->prev_kprobe.status = kcb->kprobe_status;
+	unsigned int i;
+	i = atomic_add_return(1, &kcb->prev_kprobe_index);
+	kcb->prev_kprobe[i-1].kp = kprobe_running();
+	kcb->prev_kprobe[i-1].status = kcb->kprobe_status;
 }
 
 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
-	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
-	kcb->kprobe_status = kcb->prev_kprobe.status;
+	unsigned int i;
+	i = atomic_sub_return(1, &kcb->prev_kprobe_index);
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i].kp;
+	kcb->kprobe_status = kcb->prev_kprobe[i].status;
 }
 
 static void __kprobes set_current_kprobe(struct kprobe *p,
Index: work/include/asm-ia64/kprobes.h
=================================--- work.orig/include/asm-ia64/kprobes.h	2007-02-04 10:44:54.000000000 -0800
+++ work/include/asm-ia64/kprobes.h	2007-05-08 13:30:43.000000000 -0700
@@ -71,13 +71,15 @@
 
 #define	MAX_PARAM_RSE_SIZE	(0x60+0x60/0x3f)
 /* per-cpu kprobe control block */
+#define ARCH_PREV_KPROBE_SZ 2
 struct kprobe_ctlblk {
 	unsigned long kprobe_status;
 	struct pt_regs jprobe_saved_regs;
 	unsigned long jprobes_saved_stacked_regs[MAX_PARAM_RSE_SIZE];
 	unsigned long *bsp;
 	unsigned long cfm;
-	struct prev_kprobe prev_kprobe;
+	atomic_t prev_kprobe_index;
+	struct prev_kprobe prev_kprobe[ARCH_PREV_KPROBE_SZ];
 };
 
 #define JPROBE_ENTRY(pentry)	(kprobe_opcode_t *)pentry