Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755665Ab3CEJgP (ORCPT ); Tue, 5 Mar 2013 04:36:15 -0500 Received: from g6t0185.atlanta.hp.com ([15.193.32.62]:21675 "EHLO g6t0185.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755626Ab3CEJgL (ORCPT ); Tue, 5 Mar 2013 04:36:11 -0500 Message-ID: <1362476164.2225.52.camel@buesod1.americas.hpqcorp.net> Subject: [PATCH v2 2/4] ipc: introduce obtaining a lockless ipc object From: Davidlohr Bueso To: Linus Torvalds , Rik van Riel Cc: Emmanuel Benisty , "Vinod, Chegu" , "Low, Jason" , Peter Zijlstra , "H. Peter Anvin" , Andrew Morton , aquini@redhat.com, Michel Lespinasse , Ingo Molnar , Larry Woodman , Linux Kernel Mailing List , Steven Rostedt , Thomas Gleixner Date: Tue, 05 Mar 2013 01:36:04 -0800 Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4 (3.4.4-2.fc17) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4090 Lines: 148 Through ipc_lock() and therefore ipc_lock_check() we currently return the locked ipc object. This is not necessary for all situations an can, therefore, incur in unnecessary ipc lock contention. Introduce, analogous, ipc_obtain_object() and ipc_obtain_object_check() functions that only lookup and return the ipc object. Both these functions must be called within the RCU read critical section. Signed-off-by: Davidlohr Bueso Reviewed-by: Chegu Vinod Acked-by: Michel Lespinasse --- ipc/util.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++------------ ipc/util.h | 2 ++ 2 files changed, 60 insertions(+), 13 deletions(-) diff --git a/ipc/util.c b/ipc/util.c index 464a8ab..65c3d6c 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -668,6 +668,28 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) } /** + * ipc_obtain_object + * @ids: ipc identifier set + * @id: ipc id to look for + * + * Look for an id in the ipc ids idr and return associated ipc object. + * + * Call inside the RCU critical section. + * The ipc object is *not* locked on exit. + */ +struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id) +{ + struct kern_ipc_perm *out; + int lid = ipcid_to_idx(id); + + out = idr_find(&ids->ipcs_idr, lid); + if (!out) + return ERR_PTR(-EINVAL); + + return out; +} + +/** * ipc_lock - Lock an ipc structure without rw_mutex held * @ids: IPC identifier set * @id: ipc id to look for @@ -680,27 +702,50 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id) { struct kern_ipc_perm *out; - int lid = ipcid_to_idx(id); - + rcu_read_lock(); - out = idr_find(&ids->ipcs_idr, lid); - if (out == NULL) { - rcu_read_unlock(); - return ERR_PTR(-EINVAL); - } + out = ipc_obtain_object(ids, id); + if (IS_ERR(out)) + goto err1; spin_lock(&out->lock); - + /* ipc_rmid() may have already freed the ID while ipc_lock * was spinning: here verify that the structure is still valid */ - if (out->deleted) { - spin_unlock(&out->lock); - rcu_read_unlock(); - return ERR_PTR(-EINVAL); - } + if (out->deleted) + goto err0; return out; +err0: + spin_unlock(&out->lock); +err1: + rcu_read_unlock(); + return ERR_PTR(-EINVAL); +} + +/** + * ipc_obtain_object_check + * @ids: ipc identifier set + * @id: ipc id to look for + * + * Similar to ipc_obtain_object() but also checks + * the ipc object reference counter. + * + * Call inside the RCU critical section. + * The ipc object is *not* locked on exit. + */ +struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id) +{ + struct kern_ipc_perm *out = ipc_obtain_object(ids, id); + + if (IS_ERR(out)) + goto out; + + if (ipc_checkid(out, id)) + return ERR_PTR(-EIDRM); +out: + return out; } struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id) diff --git a/ipc/util.h b/ipc/util.h index ac1480a..bfc8d4e 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -123,6 +123,7 @@ void ipc_rcu_getref(void *ptr); void ipc_rcu_putref(void *ptr); struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int); +struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id); void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out); void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out); @@ -168,6 +169,7 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm) } struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id); +struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id); int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids, struct ipc_ops *ops, struct ipc_params *params); void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids, -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/