Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752578Ab3CBAQq (ORCPT ); Fri, 1 Mar 2013 19:16:46 -0500 Received: from g4t0017.houston.hp.com ([15.201.24.20]:27698 "EHLO g4t0017.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752413Ab3CBAQn (ORCPT ); Fri, 1 Mar 2013 19:16:43 -0500 Message-ID: <1362183400.3420.24.camel@buesod1.americas.hpqcorp.net> Subject: [RFC PATCH 1/2] ipc: introduce obtaining a lockless ipc object From: Davidlohr Bueso To: Linus Torvalds , Rik van Riel Cc: "Vinod, Chegu" , "Low, Jason" , linux-tip-commits@vger.kernel.org, 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: Fri, 01 Mar 2013 16:16:40 -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: 3767 Lines: 128 Through ipc_lock() and, therefore, ipc_lock_check() we currently return the locked ipc object. This is not necessary for all situations, thus introduce, analogous, ipc_obtain_object and ipc_obtain_object_check functions that only mark the RCU read critical region without acquiring the lock and return the ipc object. Signed-off-by: Davidlohr Bueso --- ipc/util.c | 42 ++++++++++++++++++++++++++++++++---------- ipc/util.h | 2 ++ 2 files changed, 34 insertions(+), 10 deletions(-) diff --git a/ipc/util.c b/ipc/util.c index 464a8ab..902f282 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -667,6 +667,21 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) out->seq = in->seq; } +struct kern_ipc_perm *ipc_obtain_object(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) { + rcu_read_unlock(); + return ERR_PTR(-EINVAL); + } + + return out; +} + /** * ipc_lock - Lock an ipc structure without rw_mutex held * @ids: IPC identifier set @@ -679,18 +694,13 @@ 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); + struct kern_ipc_perm *out = ipc_obtain_object(ids, id); - rcu_read_lock(); - out = idr_find(&ids->ipcs_idr, lid); - if (out == NULL) { - rcu_read_unlock(); + if (!out) return ERR_PTR(-EINVAL); - } 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 */ @@ -703,6 +713,18 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id) return out; } +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)) + return out; + + if (ipc_checkid(out, id)) + return ERR_PTR(-EIDRM); + return out; +} + struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id) { struct kern_ipc_perm *out; @@ -784,7 +806,7 @@ struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns, int err; down_write(&ids->rw_mutex); - ipcp = ipc_lock_check(ids, id); + ipcp = ipc_obtain_object_check(ids, id); if (IS_ERR(ipcp)) { err = PTR_ERR(ipcp); goto out_up; @@ -801,7 +823,7 @@ struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns, return ipcp; err = -EPERM; - ipc_unlock(ipcp); + rcu_read_unlock(); out_up: up_write(&ids->rw_mutex); return ERR_PTR(err); diff --git a/ipc/util.h b/ipc/util.h index eeb79a1..2c68035 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); @@ -173,6 +174,7 @@ 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/