[S390] kprobes: activation and deactivation

Replace set_current_kprobe/reset_current_kprobe/save_previous_kprobe/
restore_previous_kprobe with a simpler scheme push_kprobe/pop_kprobe.
The mini kprobes stack can store up to two active kprobes.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 27 insertions, 32 deletions

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index fcbc25836879..f68eaaaa8062 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -214,25 +214,29 @@ static void __kprobes disable_singlestep(struct kprobe_ctlblk *kcb,
         regs->psw.addr = ip | PSW_ADDR_AMODE;
 }
 
-
-static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+/*
+ * Activate a kprobe by storing its pointer to current_kprobe. The
+ * previous kprobe is stored in kcb->prev_kprobe. A stack of up to
+ * two kprobes can be active, see KPROBE_REENTER.
+ */
+static void __kprobes push_kprobe(struct kprobe_ctlblk *kcb, struct kprobe *p)
 {
-        kcb->prev_kprobe.kp = kprobe_running();
+        kcb->prev_kprobe.kp = __get_cpu_var(current_kprobe);
         kcb->prev_kprobe.status = kcb->kprobe_status;
+        __get_cpu_var(current_kprobe) = p;
 }
 
-static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+/*
+ * Deactivate a kprobe by backing up to the previous state. If the
+ * current state is KPROBE_REENTER prev_kprobe.kp will be non-NULL,
+ * for any other state prev_kprobe.kp will be NULL.
+ */
+static void __kprobes pop_kprobe(struct kprobe_ctlblk *kcb)
 {
         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
         kcb->kprobe_status = kcb->prev_kprobe.status;
 }
 
-static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
-                                                struct kprobe_ctlblk *kcb)
-{
-        __get_cpu_var(current_kprobe) = p;
-}
-
 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                         struct pt_regs *regs)
 {
@@ -261,14 +265,16 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
         if (kprobe_running()) {
                 p = get_kprobe(addr);
                 if (p) {
-                        /* 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.
+                        /*
+                         * We have hit a kprobe while another is still
+                         * active. This can happen in the pre and post
+                         * handler. Single step the instruction of the
+                         * new probe but do not call any handler function
+                         * of this secondary kprobe.
+                         * push_kprobe and pop_kprobe saves and restores
+                         * the currently active kprobe.
                          */
-                        save_previous_kprobe(kcb);
-                        set_current_kprobe(p, regs, kcb);
+                        push_kprobe(kcb, p);
                         kprobes_inc_nmissed_count(p);
                         enable_singlestep(kcb, regs,
                                           (unsigned long) p->ainsn.insn);
@@ -294,7 +300,7 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                 goto no_kprobe;
 
         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
-        set_current_kprobe(p, regs, kcb);
+        push_kprobe(kcb, p);
         if (p->pre_handler && p->pre_handler(p, regs))
                 /* handler has already set things up, so skip ss setup */
                 return 1;
@@ -395,7 +401,7 @@ static int __kprobes trampoline_probe_handler(struct kprobe *p,
 
         regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
 
-        reset_current_kprobe();
+        pop_kprobe(get_kprobe_ctlblk());
         kretprobe_hash_unlock(current, &flags);
         preempt_enable_no_resched();
 
@@ -457,14 +463,7 @@ static int __kprobes post_kprobe_handler(struct pt_regs *regs)
         }
 
         resume_execution(cur, regs);
-
-        /*Restore back the original saved kprobes variables and continue. */
-        if (kcb->kprobe_status == KPROBE_REENTER) {
-                restore_previous_kprobe(kcb);
-                goto out;
-        }
-        reset_current_kprobe();
-out:
+        pop_kprobe(kcb);
         preempt_enable_no_resched();
 
         /*
@@ -499,11 +498,7 @@ static int __kprobes kprobe_trap_handler(struct pt_regs *regs, int trapnr)
                  * normal page fault.
                  */
                 disable_singlestep(kcb, regs, (unsigned long) cur->addr);
-                if (kcb->kprobe_status == KPROBE_REENTER)
-                        restore_previous_kprobe(kcb);
-                else {
-                        reset_current_kprobe();
-                }
+                pop_kprobe(kcb);
                 preempt_enable_no_resched();
                 break;
         case KPROBE_HIT_ACTIVE: