From: Stephen Smalley <sds@tycho.nsa.gov> To: Waiman Long <Waiman.Long@hp.com>, Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@parisplace.org>, James Morris <james.l.morris@oracle.com>, "Serge E. Hallyn" <serge@hallyn.com>, selinux@tycho.nsa.gov Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, Yury <yury.norov@gmail.com>, Scott J Norton <scott.norton@hp.com>, Douglas Hatch <doug.hatch@hp.com> Subject: Re: [PATCH v3] selinux: reduce locking overhead in inode_free_security() Date: Mon, 15 Jun 2015 13:18:24 -0400 [thread overview] Message-ID: <557F08E0.4040007@tycho.nsa.gov> (raw) In-Reply-To: <1434388419-14850-1-git-send-email-Waiman.Long@hp.com> On 06/15/2015 01:13 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 <Waiman.Long@hp.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> > --- > 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. > > 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 >
WARNING: multiple messages have this Message-ID (diff)
From: Stephen Smalley <sds@tycho.nsa.gov> To: Waiman Long <Waiman.Long@hp.com>, Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@parisplace.org>, James Morris <james.l.morris@oracle.com>, "Serge E. Hallyn" <serge@hallyn.com>, selinux@tycho.nsa.gov Cc: Yury <yury.norov@gmail.com>, Scott J Norton <scott.norton@hp.com>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Douglas Hatch <doug.hatch@hp.com> Subject: Re: [PATCH v3] selinux: reduce locking overhead in inode_free_security() Date: Mon, 15 Jun 2015 13:18:24 -0400 [thread overview] Message-ID: <557F08E0.4040007@tycho.nsa.gov> (raw) In-Reply-To: <1434388419-14850-1-git-send-email-Waiman.Long@hp.com> On 06/15/2015 01:13 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 <Waiman.Long@hp.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> > --- > 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. > > 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 >
next prev parent reply other threads:[~2015-06-16 12:11 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-06-15 17:13 [PATCH v3] selinux: reduce locking overhead in inode_free_security() Waiman Long 2015-06-15 17:13 ` Waiman Long 2015-06-15 17:18 ` Stephen Smalley [this message] 2015-06-15 17:18 ` Stephen Smalley 2015-06-15 20:33 ` Yury 2015-06-15 20:33 ` Yury 2015-06-18 19:07 ` Paul Moore 2015-06-18 19:07 ` Paul Moore
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=557F08E0.4040007@tycho.nsa.gov \ --to=sds@tycho.nsa.gov \ --cc=Waiman.Long@hp.com \ --cc=doug.hatch@hp.com \ --cc=eparis@parisplace.org \ --cc=james.l.morris@oracle.com \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-security-module@vger.kernel.org \ --cc=paul@paul-moore.com \ --cc=raghavendra.kt@linux.vnet.ibm.com \ --cc=scott.norton@hp.com \ --cc=selinux@tycho.nsa.gov \ --cc=serge@hallyn.com \ --cc=yury.norov@gmail.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.