[PATCH] kprobes: Temporary disarming of reentrant probe for ppc64

This patch includes ppc64 architecture specific changes to support temporary
disarming on reentrancy of probes.

Signed-of-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/ppc64/kernel/kprobes.c b/arch/ppc64/kernel/kprobes.c
index 8c0920a6d03e277d36c8f3d2767db8f363eb6e4e..782ce3efa2c10d04718d70157d7acb9d56786039 100644 (file)
--- a/arch/ppc64/kernel/kprobes.c
+++ b/arch/ppc64/kernel/kprobes.c
@@ -36,12 +36,10 @@
 #include <asm/kdebug.h>
 #include <asm/sstep.h>
 
-/* kprobe_status settings */
-#define KPROBE_HIT_ACTIVE      0x00000001
-#define KPROBE_HIT_SS          0x00000002
-
 static struct kprobe *current_kprobe;
 static unsigned long kprobe_status, kprobe_saved_msr;
+static struct kprobe *kprobe_prev;
+static unsigned long kprobe_status_prev, kprobe_saved_msr_prev;
 static struct pt_regs jprobe_saved_regs;
 
 int arch_prepare_kprobe(struct kprobe *p)
@@ -93,6 +91,20 @@ static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
                regs->nip = (unsigned long)&p->ainsn.insn;
 }
 
+static inline void save_previous_kprobe(void)
+{
+       kprobe_prev = current_kprobe;
+       kprobe_status_prev = kprobe_status;
+       kprobe_saved_msr_prev = kprobe_saved_msr;
+}
+
+static inline void restore_previous_kprobe(void)
+{
+       current_kprobe = kprobe_prev;
+       kprobe_status = kprobe_status_prev;
+       kprobe_saved_msr = kprobe_saved_msr_prev;
+}
+
 static inline int kprobe_handler(struct pt_regs *regs)
 {
        struct kprobe *p;
@@ -111,9 +123,19 @@ static inline int kprobe_handler(struct pt_regs *regs)
                                unlock_kprobes();
                                goto no_kprobe;
                        }
-                       arch_disarm_kprobe(p);
-                       regs->nip = (unsigned long)p->addr;
-                       ret = 1;
+                       /* We have reentered the kprobe_handler(), since
+                        * another probe was hit while within the handler.
+                        * We here save the original kprobes variables and
+                        * just single step on the instruction of the new probe
+                        * without calling any user handlers.
+                        */
+                       save_previous_kprobe();
+                       current_kprobe = p;
+                       kprobe_saved_msr = regs->msr;
+                       p->nmissed++;
+                       prepare_singlestep(p, regs);
+                       kprobe_status = KPROBE_REENTER;
+                       return 1;
                } else {
                        p = current_kprobe;
                        if (p->break_handler && p->break_handler(p, regs)) {
@@ -195,13 +217,21 @@ static inline int post_kprobe_handler(struct pt_regs *regs)
        if (!kprobe_running())
                return 0;
 
-       if (current_kprobe->post_handler)
+       if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
+               kprobe_status = KPROBE_HIT_SSDONE;
                current_kprobe->post_handler(current_kprobe, regs, 0);
+       }
 
        resume_execution(current_kprobe, regs);
        regs->msr |= kprobe_saved_msr;
 
+       /*Restore back the original saved kprobes variables and continue. */
+       if (kprobe_status == KPROBE_REENTER) {
+               restore_previous_kprobe();
+               goto out;
+       }
        unlock_kprobes();
+out:
        preempt_enable_no_resched();
 
        /*