idr: make idr_remove rcu-safe

Introduce the free_layer() routine: it is the one that actually frees memory
after a grace period has elapsed.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Reviewed-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Jim Houston <jim.houston@comcast.net>
Cc: Pierre Peiffer <peifferp@gmail.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/idr.c b/lib/idr.c
index 21e12af..3476f82 100644 (file)
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -52,6 +52,19 @@ static struct idr_layer *get_from_free_list(struct idr *idp)
        return(p);
 }
 
+static void idr_layer_rcu_free(struct rcu_head *head)
+{
+       struct idr_layer *layer;
+
+       layer = container_of(head, struct idr_layer, rcu_head);
+       kmem_cache_free(idr_layer_cache, layer);
+}
+
+static inline void free_layer(struct idr_layer *p)
+{
+       call_rcu(&p->rcu_head, idr_layer_rcu_free);
+}
+
 /* only called when idp->lock is held */
 static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
 {
@@ -331,6 +344,7 @@ static void sub_remove(struct idr *idp, int shift, int id)
        struct idr_layer *p = idp->top;
        struct idr_layer **pa[MAX_LEVEL];
        struct idr_layer ***paa = &pa[0];
+       struct idr_layer *to_free;
        int n;
 
        *paa = NULL;
@@ -346,13 +360,18 @@ static void sub_remove(struct idr *idp, int shift, int id)
        n = id & IDR_MASK;
        if (likely(p != NULL && test_bit(n, &p->bitmap))){
                __clear_bit(n, &p->bitmap);
-               p->ary[n] = NULL;
+               rcu_assign_pointer(p->ary[n], NULL);
+               to_free = NULL;
                while(*paa && ! --((**paa)->count)){
-                       move_to_free_list(idp, **paa);
+                       if (to_free)
+                               free_layer(to_free);
+                       to_free = **paa;
                        **paa-- = NULL;
                }
                if (!*paa)
                        idp->layers = 0;
+               if (to_free)
+                       free_layer(to_free);
        } else
                idr_remove_warning(id);
 }
@@ -365,22 +384,34 @@ static void sub_remove(struct idr *idp, int shift, int id)
 void idr_remove(struct idr *idp, int id)
 {
        struct idr_layer *p;
+       struct idr_layer *to_free;
 
        /* Mask off upper bits we don't use for the search. */
        id &= MAX_ID_MASK;
 
        sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
        if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
-           idp->top->ary[0]) {  // We can drop a layer
-
+           idp->top->ary[0]) {
+               /*
+                * Single child at leftmost slot: we can shrink the tree.
+                * This level is not needed anymore since when layers are
+                * inserted, they are inserted at the top of the existing
+                * tree.
+                */
+               to_free = idp->top;
                p = idp->top->ary[0];
-               idp->top->bitmap = idp->top->count = 0;
-               move_to_free_list(idp, idp->top);
-               idp->top = p;
+               rcu_assign_pointer(idp->top, p);
                --idp->layers;
+               to_free->bitmap = to_free->count = 0;
+               free_layer(to_free);
        }
        while (idp->id_free_cnt >= IDR_FREE_MAX) {
                p = get_from_free_list(idp);
+               /*
+                * Note: we don't call the rcu callback here, since the only
+                * layers that fall into the freelist are those that have been
+                * preallocated.
+                */
                kmem_cache_free(idr_layer_cache, p);
        }
        return;
@@ -421,15 +452,13 @@ void idr_remove_all(struct idr *idp)
 
                id += 1 << n;
                while (n < fls(id)) {
-                       if (p) {
-                               memset(p, 0, sizeof *p);
-                               move_to_free_list(idp, p);
-                       }
+                       if (p)
+                               free_layer(p);
                        n += IDR_BITS;
                        p = *--paa;
                }
        }
-       idp->top = NULL;
+       rcu_assign_pointer(idp->top, NULL);
        idp->layers = 0;
 }
 EXPORT_SYMBOL(idr_remove_all);
@@ -546,7 +575,7 @@ EXPORT_SYMBOL(idr_for_each);
  * A -ENOENT return indicates that @id was not found.
  * A -EINVAL return indicates that @id was not within valid constraints.
  *
- * The caller must serialize vs idr_find(), idr_get_new(), and idr_remove().
+ * The caller must serialize with writers.
  */
 void *idr_replace(struct idr *idp, void *ptr, int id)
 {
@@ -572,7 +601,7 @@ void *idr_replace(struct idr *idp, void *ptr, int id)
                return ERR_PTR(-ENOENT);
 
        old_p = p->ary[n];
-       p->ary[n] = ptr;
+       rcu_assign_pointer(p->ary[n], ptr);
 
        return old_p;
 }