kprobes: kretprobes simplifications

 - consolidate duplicate code in all arch_prepare_kretprobe instances
   into common code
 - replace various odd helpers that use hlist_for_each_entry to get
   the first elemenet of a list with either a hlist_for_each_entry_save
   or an opencoded access to the first element in the caller
 - inline add_rp_inst into it's only remaining caller
 - use kretprobe_inst_table_head instead of opencoding it

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 21 insertions, 43 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 22857003a65b..f58f171bd65f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -358,46 +358,6 @@ void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
 }
 
 /* Called with kretprobe_lock held */
-struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
-{
-        struct hlist_node *node;
-        struct kretprobe_instance *ri;
-        hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
-                return ri;
-        return NULL;
-}
-
-/* Called with kretprobe_lock held */
-static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
-                                                              *rp)
-{
-        struct hlist_node *node;
-        struct kretprobe_instance *ri;
-        hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
-                return ri;
-        return NULL;
-}
-
-/* Called with kretprobe_lock held */
-void __kprobes add_rp_inst(struct kretprobe_instance *ri)
-{
-        /*
-         * Remove rp inst off the free list -
-         * Add it back when probed function returns
-         */
-        hlist_del(&ri->uflist);
-
-        /* Add rp inst onto table */
-        INIT_HLIST_NODE(&ri->hlist);
-        hlist_add_head(&ri->hlist,
-                        &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
-
-        /* Also add this rp inst to the used list. */
-        INIT_HLIST_NODE(&ri->uflist);
-        hlist_add_head(&ri->uflist, &ri->rp->used_instances);
-}
-
-/* Called with kretprobe_lock held */
 void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
                                 struct hlist_head *head)
 {
@@ -450,7 +410,9 @@ void __kprobes kprobe_flush_task(struct task_struct *tk)
 static inline void free_rp_inst(struct kretprobe *rp)
 {
         struct kretprobe_instance *ri;
-        while ((ri = get_free_rp_inst(rp)) != NULL) {
+        struct hlist_node *pos, *next;
+
+        hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, uflist) {
                 hlist_del(&ri->uflist);
                 kfree(ri);
         }
@@ -732,7 +694,21 @@ static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 
         /*TODO: consider to only swap the RA after the last pre_handler fired */
         spin_lock_irqsave(&kretprobe_lock, flags);
-        arch_prepare_kretprobe(rp, regs);
+        if (!hlist_empty(&rp->free_instances)) {
+                struct kretprobe_instance *ri;
+
+                ri = hlist_entry(rp->free_instances.first,
+                                 struct kretprobe_instance, uflist);
+                ri->rp = rp;
+                ri->task = current;
+                arch_prepare_kretprobe(ri, regs);
+
+                /* XXX(hch): why is there no hlist_move_head? */
+                hlist_del(&ri->uflist);
+                hlist_add_head(&ri->uflist, &ri->rp->used_instances);
+                hlist_add_head(&ri->hlist, kretprobe_inst_table_head(ri->task));
+        } else
+                rp->nmissed++;
         spin_unlock_irqrestore(&kretprobe_lock, flags);
         return 0;
 }
@@ -795,11 +771,13 @@ void __kprobes unregister_kretprobe(struct kretprobe *rp)
 {
         unsigned long flags;
         struct kretprobe_instance *ri;
+        struct hlist_node *pos, *next;
 
         unregister_kprobe(&rp->kp);
+
         /* No race here */
         spin_lock_irqsave(&kretprobe_lock, flags);
-        while ((ri = get_used_rp_inst(rp)) != NULL) {
+        hlist_for_each_entry_safe(ri, pos, next, &rp->used_instances, uflist) {
                 ri->rp = NULL;
                 hlist_del(&ri->uflist);
         }