Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756516AbbFRTIG (ORCPT ); Thu, 18 Jun 2015 15:08:06 -0400 Received: from mail-qg0-f52.google.com ([209.85.192.52]:36588 "EHLO mail-qg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752251AbbFRTH5 (ORCPT ); Thu, 18 Jun 2015 15:07:57 -0400 From: Paul Moore To: Waiman Long Cc: Stephen Smalley , Eric Paris , James Morris , "Serge E. Hallyn" , selinux@tycho.nsa.gov, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Raghavendra K T , Yury , Scott J Norton , Douglas Hatch Subject: Re: [PATCH v3] selinux: reduce locking overhead in inode_free_security() Date: Thu, 18 Jun 2015 15:07:54 -0400 Message-ID: <4547030.ymnAKE063H@sifl> User-Agent: KMail/4.14.8 (Linux/3.16.7-gentoo; KDE/4.14.9; x86_64; ; ) In-Reply-To: <1434388419-14850-1-git-send-email-Waiman.Long@hp.com> References: <1434388419-14850-1-git-send-email-Waiman.Long@hp.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2894 Lines: 70 On Monday, June 15, 2015 01:13:39 PM Waiman Long wrote: > The inode_free_security() function just took the superblock's isec_lock > before checking and trying to remove the inode security struct from the > linked list. In many cases, the list was empty and so the lock taking > is wasteful as no useful work is done. On multi-socket systems with > a large number of CPUs, there can also be a fair amount of spinlock > contention on the isec_lock if many tasks are exiting at the same time. > > This patch changes the code to check the state of the list first before > taking the lock and attempting to dequeue it. The list_del_init() > can be called more than once on the same list with no harm as long > as they are properly serialized. It should not be possible to have > inode_free_security() called concurrently with list_add(). For better > safety, however, we use list_empty_careful() here even though it is > still not completely safe in case that happens. > > Signed-off-by: Waiman Long > --- > security/selinux/hooks.c | 17 ++++++++++++++--- > 1 files changed, 14 insertions(+), 3 deletions(-) > > v1->v2: > - Take out the second list_empty() test inside the lock. > > v2->v3: > - Fix incorrent comment and commit log message. Thanks for the patch and the discussion; I've added this to the SELinux next- queue branch and I'll push it to selinux#next as soon as the merge window closes. > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 7dade28..2a99804 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -254,10 +254,21 @@ static void inode_free_security(struct inode *inode) > struct inode_security_struct *isec = inode->i_security; > struct superblock_security_struct *sbsec = inode->i_sb->s_security; > > - spin_lock(&sbsec->isec_lock); > - if (!list_empty(&isec->list)) > + /* > + * As not all inode security structures are in a list, we check for > + * empty list outside of the lock to make sure that we won't waste > + * time taking a lock doing nothing. > + * > + * The list_del_init() function can be safely called more than once. > + * It should not be possible for this function to be called with > + * concurrent list_add(), but for better safety against future changes > + * in the code, we use list_empty_careful() here. > + */ > + if (!list_empty_careful(&isec->list)) { > + spin_lock(&sbsec->isec_lock); > list_del_init(&isec->list); > - spin_unlock(&sbsec->isec_lock); > + spin_unlock(&sbsec->isec_lock); > + } > > /* > * The inode may still be referenced in a path walk and -- paul moore www.paul-moore.com -- 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/