[PATCH] Kprobes: preempt_disable/enable() simplification

Reorganize the preempt_disable/enable calls to eliminate the extra preempt
depth.  Changes based on Paul McKenney's review suggestions for the kprobes
RCU changeset.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 10 deletions

diff --git a/arch/ppc64/kernel/kprobes.c b/arch/ppc64/kernel/kprobes.c
index e0a25b35437f..511af54e6230 100644
--- a/arch/ppc64/kernel/kprobes.c
+++ b/arch/ppc64/kernel/kprobes.c
@@ -148,7 +148,14 @@ static inline int kprobe_handler(struct pt_regs *regs)
         struct kprobe *p;
         int ret = 0;
         unsigned int *addr = (unsigned int *)regs->nip;
-        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+        struct kprobe_ctlblk *kcb;
+
+        /*
+         * We don't want to be preempted for the entire
+         * duration of kprobe processing
+         */
+        preempt_disable();
+        kcb = get_kprobe_ctlblk();
 
         /* Check we're not actually recursing */
         if (kprobe_running()) {
@@ -207,11 +214,6 @@ static inline int kprobe_handler(struct pt_regs *regs)
                 goto no_kprobe;
         }
 
-        /*
-         * This preempt_disable() matches the preempt_enable_no_resched()
-         * in post_kprobe_handler().
-         */
-        preempt_disable();
         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
         set_current_kprobe(p, regs, kcb);
         if (p->pre_handler && p->pre_handler(p, regs))
@@ -224,6 +226,7 @@ ss_probe:
         return 1;
 
 no_kprobe:
+        preempt_enable_no_resched();
         return ret;
 }
 
@@ -296,8 +299,8 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 
         /*
          * By returning a non-zero value, we are telling
-         * kprobe_handler() that we have handled unlocking
-         * and re-enabling preemption.
+         * kprobe_handler() that we don't want the post_handler
+         * to run (and have re-enabled preemption)
          */
         return 1;
 }
@@ -385,7 +388,6 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
         struct die_args *args = (struct die_args *)data;
         int ret = NOTIFY_DONE;
 
-        rcu_read_lock();
         switch (val) {
         case DIE_BPT:
                 if (kprobe_handler(args->regs))
@@ -396,14 +398,16 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                         ret = NOTIFY_STOP;
                 break;
         case DIE_PAGE_FAULT:
+                /* kprobe_running() needs smp_processor_id() */
+                preempt_disable();
                 if (kprobe_running() &&
                     kprobe_fault_handler(args->regs, args->trapnr))
                         ret = NOTIFY_STOP;
+                preempt_enable();
                 break;
         default:
                 break;
         }
-        rcu_read_unlock();
         return ret;
 }
 
@@ -440,6 +444,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
          * saved regs...
          */
         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+        preempt_enable_no_resched();
         return 1;
 }