LinuxLists.cc - [PATCH 0/3] rcu - removing superfluous rcu_read_lock

2010-11-01 19:16:53

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

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 <[email protected]>
---
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(-)

2010-11-01 19:16:36

by Jiri Olsa

[permalink] [raw]

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

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 <[email protected]>
---
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

2010-11-01 19:16:41

by Jiri Olsa

[permalink] [raw]

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

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 <[email protected]>
---
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

2010-11-01 19:16:33

by Jiri Olsa

[permalink] [raw]

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

2010-11-01 20:33:06

by David Miller

[permalink] [raw]

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

From: Jiri Olsa <[email protected]>
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 <[email protected]>

Acked-by: David S. Miller <[email protected]>

2010-11-01 21:47:19

by Paul Moore

[permalink] [raw]

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

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 <[email protected]>

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

2010-11-01 22:42:29

by Paolo Bonzini

[permalink] [raw]

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

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

2010-11-02 07:23:28

by Jiri Olsa

[permalink] [raw]

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

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

2010-11-02 17:55:03

by Li Zefan

[permalink] [raw]

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

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 <[email protected]>

Reviewed-by: Li Zefan <[email protected]>

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;