Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933052AbbFJURt (ORCPT ); Wed, 10 Jun 2015 16:17:49 -0400 Received: from g9t5008.houston.hp.com ([15.240.92.66]:41396 "EHLO g9t5008.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751688AbbFJURk (ORCPT ); Wed, 10 Jun 2015 16:17:40 -0400 From: Waiman Long To: Paul Moore , Stephen Smalley , Eric Paris , James Morris , "Serge E. Hallyn" , selinux@tycho.nsa.gov Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Scott J Norton , Douglas Hatch , Waiman Long Subject: [PATCH] selinux: reduce locking overhead in inode_free_security() Date: Wed, 10 Jun 2015 16:17:26 -0400 Message-Id: <1433967446-44555-1-git-send-email-Waiman.Long@hp.com> X-Mailer: git-send-email 1.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2163 Lines: 53 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 -- 1.7.1 -- 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/