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Date: Fri, 30 May 2008 01:24:49 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Nadia.Derbey@...l.net
Cc: manfred@...orfullife.com, lnxninja@...ux.vnet.ibm.com,
linux-kernel@...r.kernel.org, efault@....de,
akpm@...ux-foundation.org
Subject: Re: [PATCH 7/9] Make idr_remove rcu-safe
On Wed, May 07, 2008 at 01:36:00PM +0200, Nadia.Derbey@...l.net wrote:
> [PATCH 07/09]
>
> This patch introduces the free_layer() routine: it is the one that actually
> frees memory after a grace period has elapsed.
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Nadia Derbey <Nadia.Derbey@...l.net>
>
> ---
> lib/idr.c | 59 ++++++++++++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 44 insertions(+), 15 deletions(-)
>
> Index: linux-2.6.25-mm1/lib/idr.c
> ===================================================================
> --- linux-2.6.25-mm1.orig/lib/idr.c 2008-05-06 18:06:43.000000000 +0200
> +++ linux-2.6.25-mm1/lib/idr.c 2008-05-07 09:07:31.000000000 +0200
> @@ -52,6 +52,19 @@ static struct idr_layer *get_from_free_l
> 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)
> {
> @@ -334,6 +347,7 @@ static void sub_remove(struct idr *idp,
> 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;
> @@ -349,13 +363,18 @@ static void sub_remove(struct idr *idp,
> 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);
> }
> @@ -368,25 +387,37 @@ static void sub_remove(struct idr *idp,
> 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;
> }
> + return;
> }
> EXPORT_SYMBOL(idr_remove);
>
> @@ -424,15 +455,13 @@ 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);
> @@ -549,7 +578,7 @@ 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)
> {
> @@ -575,7 +604,7 @@ void *idr_replace(struct idr *idp, void
> return ERR_PTR(-ENOENT);
>
> old_p = p->ary[n];
> - p->ary[n] = ptr;
> + rcu_assign_pointer(p->ary[n], ptr);
>
> return old_p;
> }
>
> --
--
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