[PATCH 0/3] rcu - removing superfluous rcu_read_lock_held check

[PATCH 0/3] rcu - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

hi,

the rcu_dereference_check is defined as

  #define rcu_dereference_check(p, c) \
     __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

so the caller does not need to specify rcu_read_lock_held()
condition.

Several places in kernel are spcifying rcu_read_lock_held as
rcu_dereference_check condition parameter.  I separated them
into 3 patches:

1/3 - cgroup - removing superfluous rcu_read_lock_held check
2/3 - kernel,cred,kvm,security - removing superfluous rcu_read_lock_held check
3/3 - net - removing superfluous rcu_read_lock_held check


sry if I might missed or added somebody wrongly to recipients

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 include/linux/cgroup.h             |    1 -
 include/linux/cred.h               |    1 -
 include/linux/fdtable.h            |    1 -
 include/linux/kvm_host.h           |    1 -
 include/linux/rtnetlink.h          |    3 +--
 include/net/sock.h                 |    3 +--
 kernel/cgroup.c                    |    6 ++----
 kernel/exit.c                      |    1 -
 kernel/pid.c                       |    1 -
 kernel/rcutorture.c                |    2 --
 net/mac80211/sta_info.c            |    4 ----
 net/netlabel/netlabel_domainhash.c |    3 +--
 net/netlabel/netlabel_unlabeled.c  |    3 +--
 security/keys/keyring.c            |    1 -
 14 files changed, 6 insertions(+), 25 deletions(-)

[PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

hi,
the rcu_dereference_check is defined as

	#define rcu_dereference_check(p, c) \
	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

so the caller does not need to specify rcu_read_lock_held() condition.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
 include/linux/cgroup.h |    1 -
 kernel/cgroup.c        |    6 ++----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed4ba11..caed568 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -536,7 +536,6 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
  */
 #define task_subsys_state_check(task, subsys_id, __c)			\
 	rcu_dereference_check(task->cgroups->subsys[subsys_id],		\
-			      rcu_read_lock_held() ||			\
 			      lockdep_is_held(&task->alloc_lock) ||	\
 			      cgroup_lock_is_held() || (__c))
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 66a416b..1f329a2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1687,7 +1687,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 {
 	char *start;
 	struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
-						      rcu_read_lock_held() ||
 						      cgroup_lock_is_held());
 
 	if (!dentry || cgrp == dummytop) {
@@ -1713,7 +1712,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 			break;
 
 		dentry = rcu_dereference_check(cgrp->dentry,
-					       rcu_read_lock_held() ||
 					       cgroup_lock_is_held());
 		if (!cgrp->parent)
 			continue;
@@ -4544,7 +4542,7 @@ unsigned short css_id(struct cgroup_subsys_state *css)
 	 * it's unchanged until freed.
 	 */
 	cssid = rcu_dereference_check(css->id,
-			rcu_read_lock_held() || atomic_read(&css->refcnt));
+			atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->id;
@@ -4557,7 +4555,7 @@ unsigned short css_depth(struct cgroup_subsys_state *css)
 	struct css_id *cssid;
 
 	cssid = rcu_dereference_check(css->id,
-			rcu_read_lock_held() || atomic_read(&css->refcnt));
+			atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->depth;
-- 
1.7.1

[PATCH 2/3] kernel,cred,kvm,security - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

hi,
the rcu_dereference_check is defined as

	#define rcu_dereference_check(p, c) \
	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

so the caller does not need to specify rcu_read_lock_held() condition.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
 include/linux/cred.h     |    1 -
 include/linux/fdtable.h  |    1 -
 include/linux/kvm_host.h |    1 -
 kernel/exit.c            |    1 -
 kernel/pid.c             |    1 -
 kernel/rcutorture.c      |    2 --
 security/keys/keyring.c  |    1 -
 7 files changed, 0 insertions(+), 8 deletions(-)

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 4aaeab3..a6b9afc 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -283,7 +283,6 @@ static inline void put_cred(const struct cred *_cred)
 	({								\
 		const struct task_struct *__t = (task);			\
 		rcu_dereference_check(__t->real_cred,			\
-				      rcu_read_lock_held() ||		\
 				      task_is_dead(__t));		\
 	})
 
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 133c0ba..df7e3cf 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -60,7 +60,6 @@ struct files_struct {
 
 #define rcu_dereference_check_fdtable(files, fdtfd) \
 	(rcu_dereference_check((fdtfd), \
-			       rcu_read_lock_held() || \
 			       lockdep_is_held(&(files)->file_lock) || \
 			       atomic_read(&(files)->count) == 1 || \
 			       rcu_my_thread_group_empty()))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a055742..a90a7e3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -256,7 +256,6 @@ void kvm_put_kvm(struct kvm *kvm);
 static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
 {
 	return rcu_dereference_check(kvm->memslots,
-			srcu_read_lock_held(&kvm->srcu)
 			|| lockdep_is_held(&kvm->slots_lock));
 }
 
diff --git a/kernel/exit.c b/kernel/exit.c
index b194feb..f753342 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -85,7 +85,6 @@ static void __exit_signal(struct task_struct *tsk)
 	struct tty_struct *uninitialized_var(tty);
 
 	sighand = rcu_dereference_check(tsk->sighand,
-					rcu_read_lock_held() ||
 					lockdep_tasklist_lock_is_held());
 	spin_lock(&sighand->siglock);
 
diff --git a/kernel/pid.c b/kernel/pid.c
index 39b65b6..c02adda 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -402,7 +402,6 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type)
 	if (pid) {
 		struct hlist_node *first;
 		first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
-					      rcu_read_lock_held() ||
 					      lockdep_tasklist_lock_is_held());
 		if (first)
 			result = hlist_entry(first, struct task_struct, pids[(type)].node);
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 9d8e8fb..0956a73 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -807,7 +807,6 @@ static void rcu_torture_timer(unsigned long unused)
 	idx = cur_ops->readlock();
 	completed = cur_ops->completed();
 	p = rcu_dereference_check(rcu_torture_current,
-				  rcu_read_lock_held() ||
 				  rcu_read_lock_bh_held() ||
 				  rcu_read_lock_sched_held() ||
 				  srcu_read_lock_held(&srcu_ctl));
@@ -868,7 +867,6 @@ rcu_torture_reader(void *arg)
 		idx = cur_ops->readlock();
 		completed = cur_ops->completed();
 		p = rcu_dereference_check(rcu_torture_current,
-					  rcu_read_lock_held() ||
 					  rcu_read_lock_bh_held() ||
 					  rcu_read_lock_sched_held() ||
 					  srcu_read_lock_held(&srcu_ctl));
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index d37f713..73c23f2 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -157,7 +157,6 @@ static void keyring_destroy(struct key *keyring)
 	}
 
 	klist = rcu_dereference_check(keyring->payload.subscriptions,
-				      rcu_read_lock_held() ||
 				      atomic_read(&keyring->usage) == 0);
 	if (klist) {
 		for (loop = klist->nkeys - 1; loop >= 0; loop--)
-- 
1.7.1

[PATCH 3/3] net - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

hi,
the rcu_dereference_check is defined as

	#define rcu_dereference_check(p, c) \
	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)

so the caller does not need to specify rcu_read_lock_held() condition.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
 include/linux/rtnetlink.h          |    3 +--
 include/net/sock.h                 |    3 +--
 net/mac80211/sta_info.c            |    4 ----
 net/netlabel/netlabel_domainhash.c |    3 +--
 net/netlabel/netlabel_unlabeled.c  |    3 +--
 5 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index d42f274..dfe5ba1 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -758,8 +758,7 @@ extern int lockdep_rtnl_is_held(void);
  * or RTNL. Note : Please prefer rtnl_dereference() or rcu_dereference()
  */
 #define rcu_dereference_rtnl(p)					\
-	rcu_dereference_check(p, rcu_read_lock_held() ||	\
-				 lockdep_rtnl_is_held())
+	rcu_dereference_check(p, lockdep_rtnl_is_held())
 
 /**
  * rtnl_dereference - fetch RCU pointer when updates are prevented by RTNL
diff --git a/include/net/sock.h b/include/net/sock.h
index c7a7362..bee3e9c 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1274,8 +1274,7 @@ extern unsigned long sock_i_ino(struct sock *sk);
 static inline struct dst_entry *
 __sk_dst_get(struct sock *sk)
 {
-	return rcu_dereference_check(sk->sk_dst_cache, rcu_read_lock_held() ||
-						       sock_owned_by_user(sk) ||
+	return rcu_dereference_check(sk->sk_dst_cache, sock_owned_by_user(sk) ||
 						       lockdep_is_held(&sk->sk_lock.slock));
 }
 
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 6d8f897..c879217 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -94,7 +94,6 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
 	struct sta_info *sta;
 
 	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
-				    rcu_read_lock_held() ||
 				    lockdep_is_held(&local->sta_lock) ||
 				    lockdep_is_held(&local->sta_mtx));
 	while (sta) {
@@ -102,7 +101,6 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
 		    memcmp(sta->sta.addr, addr, ETH_ALEN) == 0)
 			break;
 		sta = rcu_dereference_check(sta->hnext,
-					    rcu_read_lock_held() ||
 					    lockdep_is_held(&local->sta_lock) ||
 					    lockdep_is_held(&local->sta_mtx));
 	}
@@ -120,7 +118,6 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
 	struct sta_info *sta;
 
 	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
-				    rcu_read_lock_held() ||
 				    lockdep_is_held(&local->sta_lock) ||
 				    lockdep_is_held(&local->sta_mtx));
 	while (sta) {
@@ -129,7 +126,6 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
 		    memcmp(sta->sta.addr, addr, ETH_ALEN) == 0)
 			break;
 		sta = rcu_dereference_check(sta->hnext,
-					    rcu_read_lock_held() ||
 					    lockdep_is_held(&local->sta_lock) ||
 					    lockdep_is_held(&local->sta_mtx));
 	}
diff --git a/net/netlabel/netlabel_domainhash.c b/net/netlabel/netlabel_domainhash.c
index d37b7f8..82795a4 100644
--- a/net/netlabel/netlabel_domainhash.c
+++ b/net/netlabel/netlabel_domainhash.c
@@ -55,8 +55,7 @@ struct netlbl_domhsh_tbl {
  * should be okay */
 static DEFINE_SPINLOCK(netlbl_domhsh_lock);
 #define netlbl_domhsh_rcu_deref(p) \
-	rcu_dereference_check(p, rcu_read_lock_held() || \
-				 lockdep_is_held(&netlbl_domhsh_lock))
+	rcu_dereference_check(p, lockdep_is_held(&netlbl_domhsh_lock))
 static struct netlbl_domhsh_tbl *netlbl_domhsh = NULL;
 static struct netlbl_dom_map *netlbl_domhsh_def = NULL;
 
diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
index e2b0a68..d2f982f 100644
--- a/net/netlabel/netlabel_unlabeled.c
+++ b/net/netlabel/netlabel_unlabeled.c
@@ -116,8 +116,7 @@ struct netlbl_unlhsh_walk_arg {
  * hash table should be okay */
 static DEFINE_SPINLOCK(netlbl_unlhsh_lock);
 #define netlbl_unlhsh_rcu_deref(p) \
-	rcu_dereference_check(p, rcu_read_lock_held() || \
-				 lockdep_is_held(&netlbl_unlhsh_lock))
+	rcu_dereference_check(p, lockdep_is_held(&netlbl_unlhsh_lock))
 static struct netlbl_unlhsh_tbl *netlbl_unlhsh = NULL;
 static struct netlbl_unlhsh_iface *netlbl_unlhsh_def = NULL;
 
-- 
1.7.1

Re: [PATCH 3/3] net - removing superfluous rcu_read_lock_held check

[David Miller]

From: Jiri Olsa <jolsa@redhat.com>
Date: Mon,  1 Nov 2010 20:15:09 +0100

> the rcu_dereference_check is defined as
> 
> 	#define rcu_dereference_check(p, c) \
> 	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
> 
> so the caller does not need to specify rcu_read_lock_held() condition.
>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>

Acked-by: David S. Miller <davem@davemloft.net>

Re: [PATCH 3/3] net - removing superfluous rcu_read_lock_held check

[Paul Moore]

On Mon, 2010-11-01 at 20:15 +0100, Jiri Olsa wrote:
> hi,
> the rcu_dereference_check is defined as
> 
> 	#define rcu_dereference_check(p, c) \
> 	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
> 
> so the caller does not need to specify rcu_read_lock_held() condition.
> 
> wbr,
> jirka
> 
> 
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>

The NetLabel changes look fine to me; thanks for the cleanup.

> ---
>  include/linux/rtnetlink.h          |    3 +--
>  include/net/sock.h                 |    3 +--
>  net/mac80211/sta_info.c            |    4 ----
>  net/netlabel/netlabel_domainhash.c |    3 +--
>  net/netlabel/netlabel_unlabeled.c  |    3 +--
>  5 files changed, 4 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
> index d42f274..dfe5ba1 100644
> --- a/include/linux/rtnetlink.h
> +++ b/include/linux/rtnetlink.h
> @@ -758,8 +758,7 @@ extern int lockdep_rtnl_is_held(void);
>   * or RTNL. Note : Please prefer rtnl_dereference() or rcu_dereference()
>   */
>  #define rcu_dereference_rtnl(p)					\
> -	rcu_dereference_check(p, rcu_read_lock_held() ||	\
> -				 lockdep_rtnl_is_held())
> +	rcu_dereference_check(p, lockdep_rtnl_is_held())
>  
>  /**
>   * rtnl_dereference - fetch RCU pointer when updates are prevented by RTNL
> diff --git a/include/net/sock.h b/include/net/sock.h
> index c7a7362..bee3e9c 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1274,8 +1274,7 @@ extern unsigned long sock_i_ino(struct sock *sk);
>  static inline struct dst_entry *
>  __sk_dst_get(struct sock *sk)
>  {
> -	return rcu_dereference_check(sk->sk_dst_cache, rcu_read_lock_held() ||
> -						       sock_owned_by_user(sk) ||
> +	return rcu_dereference_check(sk->sk_dst_cache, sock_owned_by_user(sk) ||
>  						       lockdep_is_held(&sk->sk_lock.slock));
>  }
>  
> diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
> index 6d8f897..c879217 100644
> --- a/net/mac80211/sta_info.c
> +++ b/net/mac80211/sta_info.c
> @@ -94,7 +94,6 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
>  	struct sta_info *sta;
>  
>  	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
> -				    rcu_read_lock_held() ||
>  				    lockdep_is_held(&local->sta_lock) ||
>  				    lockdep_is_held(&local->sta_mtx));
>  	while (sta) {
> @@ -102,7 +101,6 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
>  		    memcmp(sta->sta.addr, addr, ETH_ALEN) == 0)
>  			break;
>  		sta = rcu_dereference_check(sta->hnext,
> -					    rcu_read_lock_held() ||
>  					    lockdep_is_held(&local->sta_lock) ||
>  					    lockdep_is_held(&local->sta_mtx));
>  	}
> @@ -120,7 +118,6 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
>  	struct sta_info *sta;
>  
>  	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
> -				    rcu_read_lock_held() ||
>  				    lockdep_is_held(&local->sta_lock) ||
>  				    lockdep_is_held(&local->sta_mtx));
>  	while (sta) {
> @@ -129,7 +126,6 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
>  		    memcmp(sta->sta.addr, addr, ETH_ALEN) == 0)
>  			break;
>  		sta = rcu_dereference_check(sta->hnext,
> -					    rcu_read_lock_held() ||
>  					    lockdep_is_held(&local->sta_lock) ||
>  					    lockdep_is_held(&local->sta_mtx));
>  	}
> diff --git a/net/netlabel/netlabel_domainhash.c b/net/netlabel/netlabel_domainhash.c
> index d37b7f8..82795a4 100644
> --- a/net/netlabel/netlabel_domainhash.c
> +++ b/net/netlabel/netlabel_domainhash.c
> @@ -55,8 +55,7 @@ struct netlbl_domhsh_tbl {
>   * should be okay */
>  static DEFINE_SPINLOCK(netlbl_domhsh_lock);
>  #define netlbl_domhsh_rcu_deref(p) \
> -	rcu_dereference_check(p, rcu_read_lock_held() || \
> -				 lockdep_is_held(&netlbl_domhsh_lock))
> +	rcu_dereference_check(p, lockdep_is_held(&netlbl_domhsh_lock))
>  static struct netlbl_domhsh_tbl *netlbl_domhsh = NULL;
>  static struct netlbl_dom_map *netlbl_domhsh_def = NULL;
>  
> diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
> index e2b0a68..d2f982f 100644
> --- a/net/netlabel/netlabel_unlabeled.c
> +++ b/net/netlabel/netlabel_unlabeled.c
> @@ -116,8 +116,7 @@ struct netlbl_unlhsh_walk_arg {
>   * hash table should be okay */
>  static DEFINE_SPINLOCK(netlbl_unlhsh_lock);
>  #define netlbl_unlhsh_rcu_deref(p) \
> -	rcu_dereference_check(p, rcu_read_lock_held() || \
> -				 lockdep_is_held(&netlbl_unlhsh_lock))
> +	rcu_dereference_check(p, lockdep_is_held(&netlbl_unlhsh_lock))
>  static struct netlbl_unlhsh_tbl *netlbl_unlhsh = NULL;
>  static struct netlbl_unlhsh_iface *netlbl_unlhsh_def = NULL;
>  

-- 
paul moore
linux @ hp

Re: [PATCH 2/3] kernel,cred,kvm,security - removing superfluous rcu_read_lock_held check

[Paolo Bonzini]

On 11/01/2010 08:15 PM, Jiri Olsa wrote:
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a055742..a90a7e3 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -256,7 +256,6 @@ void kvm_put_kvm(struct kvm *kvm);
>   static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
>   {
>   	return rcu_dereference_check(kvm->memslots,
> -			srcu_read_lock_held(&kvm->srcu)
>   			|| lockdep_is_held(&kvm->slots_lock));
>   }
>

This is an srcu_read_lock_held, which you don't touch here:

> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> index 9d8e8fb..0956a73 100644
> --- a/kernel/rcutorture.c
> +++ b/kernel/rcutorture.c
> @@ -807,7 +807,6 @@ static void rcu_torture_timer(unsigned long unused)
>  	idx = cur_ops->readlock();
>  	completed = cur_ops->completed();
>  	p = rcu_dereference_check(rcu_torture_current,
> -				  rcu_read_lock_held() ||
>  				  rcu_read_lock_bh_held() ||
>  				  rcu_read_lock_sched_held() ||
>  				  srcu_read_lock_held(&srcu_ctl));

I guess the kvm hunk is the incorrect one?

Paolo

Re: [PATCH 2/3] kernel,cred,kvm,security - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

On Mon, Nov 01, 2010 at 11:42:23PM +0100, Paolo Bonzini wrote:
> On 11/01/2010 08:15 PM, Jiri Olsa wrote:
> >diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >index a055742..a90a7e3 100644
> >--- a/include/linux/kvm_host.h
> >+++ b/include/linux/kvm_host.h
> >@@ -256,7 +256,6 @@ void kvm_put_kvm(struct kvm *kvm);
> >  static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
> >  {
> >  	return rcu_dereference_check(kvm->memslots,
> >-			srcu_read_lock_held(&kvm->srcu)
> >  			|| lockdep_is_held(&kvm->slots_lock));
> >  }
> >
> 
> This is an srcu_read_lock_held, which you don't touch here:
> 
> >diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> >index 9d8e8fb..0956a73 100644
> >--- a/kernel/rcutorture.c
> >+++ b/kernel/rcutorture.c
> >@@ -807,7 +807,6 @@ static void rcu_torture_timer(unsigned long unused)
> > 	idx = cur_ops->readlock();
> > 	completed = cur_ops->completed();
> > 	p = rcu_dereference_check(rcu_torture_current,
> >-				  rcu_read_lock_held() ||
> > 				  rcu_read_lock_bh_held() ||
> > 				  rcu_read_lock_sched_held() ||
> > 				  srcu_read_lock_held(&srcu_ctl));
> 
> I guess the kvm hunk is the incorrect one?
ops, you're right. I overlooked it, please skip the kvm hunk..

thanks,
jirka

Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check

[Li Zefan]

On 2010年11月02日 03:15, Jiri Olsa wrote:
> hi,

This..

> the rcu_dereference_check is defined as
> 
> 	#define rcu_dereference_check(p, c) \
> 	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
> 
> so the caller does not need to specify rcu_read_lock_held() condition.
>
 
> wbr,
> jirka

and this should be excluded from the changelog.

> 
> 
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>

Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>

However a nitpick:

> ---
>  include/linux/cgroup.h |    1 -
>  kernel/cgroup.c        |    6 ++----
>  2 files changed, 2 insertions(+), 5 deletions(-)
...
> @@ -4544,7 +4542,7 @@ unsigned short css_id(struct cgroup_subsys_state *css)
>  	 * it's unchanged until freed.
>  	 */
>  	cssid = rcu_dereference_check(css->id,
> -			rcu_read_lock_held() || atomic_read(&css->refcnt));
> +			atomic_read(&css->refcnt));

Now the 2 lines can be made into one line and still fit into 80 chars.

>  
>  	if (cssid)
>  		return cssid->id;
> @@ -4557,7 +4555,7 @@ unsigned short css_depth(struct cgroup_subsys_state *css)
>  	struct css_id *cssid;
>  
>  	cssid = rcu_dereference_check(css->id,
> -			rcu_read_lock_held() || atomic_read(&css->refcnt));
> +			atomic_read(&css->refcnt));

dito

>  
>  	if (cssid)
>  		return cssid->depth;