Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753158AbbFKVRa (ORCPT ); Thu, 11 Jun 2015 17:17:30 -0400 Received: from g4t3426.houston.hp.com ([15.201.208.54]:58549 "EHLO g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752561AbbFKVR1 (ORCPT ); Thu, 11 Jun 2015 17:17:27 -0400 Message-ID: <5579FAE0.9040201@hp.com> Date: Thu, 11 Jun 2015 17:17:20 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Stephen Smalley CC: Paul Moore , Eric Paris , James Morris , "Serge E. Hallyn" , selinux@tycho.nsa.gov, Scott J Norton , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Douglas Hatch Subject: Re: [PATCH] selinux: reduce locking overhead in inode_free_security() References: <1433967446-44555-1-git-send-email-Waiman.Long@hp.com> <55798149.5070404@tycho.nsa.gov> In-Reply-To: <55798149.5070404@tycho.nsa.gov> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2707 Lines: 64 On 06/11/2015 08:38 AM, Stephen Smalley wrote: > On 06/10/2015 04:17 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. We still need >> to do the empty list test inside the lock for safety reason, but it >> minimizes the chance of unnecessary spinlock contention. >> >> Signed-off-by: Waiman Long >> --- >> security/selinux/hooks.c | 17 +++++++++++++---- >> 1 files changed, 13 insertions(+), 4 deletions(-) >> >> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c >> index 7dade28..cd736c3 100644 >> --- a/security/selinux/hooks.c >> +++ b/security/selinux/hooks.c >> @@ -254,10 +254,19 @@ 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)) >> - list_del_init(&isec->list); >> - spin_unlock(&sbsec->isec_lock); >> + /* >> + * 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. Lock taking can be slow >> + * especially if the lock is being contended. We do, however, need >> + * to recheck the list again before deleting it for safety. >> + */ >> + if (!list_empty(&isec->list)) { >> + spin_lock(&sbsec->isec_lock); >> + if (!list_empty(&isec->list)) >> + list_del_init(&isec->list); >> + spin_unlock(&sbsec->isec_lock); >> + } >> >> /* >> * The inode may still be referenced in a path walk and >> > Do we really need the second list_empty() test at all? > Once removed, inode security structures are never re-added to the list. > For comparison, inode_sb_list_del() only tests list_empty() outside the > lock. > Yes, I think we can remove the second list_empty() test. I will update the patch to do that. Cheers, Longman -- 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/