[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, 20 insertions, 17 deletions

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index fddbac32d44a..96736a119c91 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -389,11 +389,11 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
         spin_unlock_irqrestore(&kretprobe_lock, flags);
         preempt_enable_no_resched();
 
-        /*
-         * By returning a non-zero value, we are telling
-         * kprobe_handler() that we have handled unlocking
-         * and re-enabling preemption
-         */
+        /*
+         * By returning a non-zero value, we are telling
+         * kprobe_handler() that we don't want the post_handler
+         * to run (and have re-enabled preemption)
+         */
         return 1;
 }
 
@@ -604,7 +604,14 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
         int ret = 0;
         struct pt_regs *regs = args->regs;
         kprobe_opcode_t *addr = (kprobe_opcode_t *)instruction_pointer(regs);
-        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();
 
         /* Handle recursion cases */
         if (kprobe_running()) {
@@ -659,11 +666,6 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
                 goto no_kprobe;
         }
 
-        /*
-         * This preempt_disable() matches the preempt_enable_no_resched()
-         * in post_kprobes_handler()
-         */
-        preempt_disable();
         set_current_kprobe(p, kcb);
         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 
@@ -681,6 +683,7 @@ ss_probe:
         return 1;
 
 no_kprobe:
+        preempt_enable_no_resched();
         return ret;
 }
 
@@ -716,9 +719,6 @@ static int __kprobes kprobes_fault_handler(struct pt_regs *regs, int trapnr)
         struct kprobe *cur = kprobe_running();
         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
-        if (!cur)
-                return 0;
-
         if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
                 return 1;
 
@@ -737,7 +737,6 @@ 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_BREAK:
                 if (pre_kprobes_handler(args))
@@ -748,12 +747,15 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                         ret = NOTIFY_STOP;
                 break;
         case DIE_PAGE_FAULT:
-                if (kprobes_fault_handler(args->regs, args->trapnr))
+                /* kprobe_running() needs smp_processor_id() */
+                preempt_disable();
+                if (kprobe_running() &&
+                        kprobes_fault_handler(args->regs, args->trapnr))
                         ret = NOTIFY_STOP;
+                preempt_enable();
         default:
                 break;
         }
-        rcu_read_unlock();
         return ret;
 }
 
@@ -785,6 +787,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
         *regs = kcb->jprobe_saved_regs;
+        preempt_enable_no_resched();
         return 1;
 }