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SubjectRe: [Cleanup PATCH] rcu: Do not use rcu_read_lock_held when calling rcu_dereference_check
On Fri 08-07-11 17:57:52, Michal Hocko wrote:
> On Fri 08-07-11 08:48:29, Paul E. McKenney wrote:
> > On Fri, Jul 08, 2011 at 03:57:39PM +0200, Michal Hocko wrote:
> > > Hi Paul,
> > > I guess that this falls down to your area because the code, even though
> > > it touches multiple areas, is RCU specific. Let me know if I should
> > > break it into smaller pieces or that I should push it through other
> > > trees.
> > >
> > > git grep -n -A3 "\<rcu_dereference_.*check" doesn't show any other
> > > variants to be "affected".
> >
> > Hello, Michal,
> >
> > Good catch, thank you!!!
> >
> > Could you please break this up by maintainer?
>
> OK, will do.

Hmm, thinking about it some more. Wouldn't it make more sense to push
this through trivial tree (CCing Jikos)? Having 5 or so patches with the
exactly same changelog sounds overkill to me.

What do you think? Could you give me your Acked-by if you are OK with
it, please?

Just for reference the original, patch:
---
From ae2bf11a3057bb10b69667d117bca6668ba644cb Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Fri, 8 Jul 2011 14:39:41 +0200
Subject: [PATCH] rcu: Do not use rcu_read_lock_held when calling
rcu_dereference_check
Since ca5ecddf (rcu: define __rcu address space modifier for sparse)
rcu_dereference_check use rcu_read_lock_held as a part of condition
automatically so callers do not have to do that as well.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
Documentation/RCU/lockdep.txt | 6 ++----
include/linux/cgroup.h | 1 -
include/linux/cred.h | 1 -
include/linux/fdtable.h | 1 -
include/linux/rtnetlink.h | 3 +--
include/net/sock.h | 3 +--
kernel/cgroup.c | 8 ++------
kernel/exit.c | 1 -
kernel/pid.c | 1 -
kernel/rcutorture.c | 2 --
kernel/sched.c | 1 -
net/mac80211/sta_info.c | 4 ----
net/netlabel/netlabel_domainhash.c | 3 +--
net/netlabel/netlabel_unlabeled.c | 3 +--
security/keys/keyring.c | 1 -
15 files changed, 8 insertions(+), 31 deletions(-)
diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt
index d7a49b2..fc5820a 100644
--- a/Documentation/RCU/lockdep.txt
+++ b/Documentation/RCU/lockdep.txt
@@ -48,13 +48,11 @@ checking of rcu_dereference() primitives:
value of the pointer itself, for example, against NULL.

The rcu_dereference_check() check expression can be any boolean
-expression, but would normally include one of the rcu_read_lock_held()
-family of functions and a lockdep expression. However, any boolean
-expression can be used. For a moderately ornate example, consider
+expression, but would normally include a lockdep expression. However, any
+boolean expression can be used. For a moderately ornate example, consider
the following:

file = rcu_dereference_check(fdt->fd[fd],
- rcu_read_lock_held() ||
lockdep_is_held(&files->file_lock) ||
atomic_read(&files->count) == 1);

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ab4ac0c..da7e4bc 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -539,7 +539,6 @@ 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/include/linux/cred.h b/include/linux/cred.h
index 8260799..f240f2f 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -284,7 +284,6 @@ 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/rtnetlink.h b/include/linux/rtnetlink.h
index bbad657..27576aa 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 c0b938c..d5b65c1 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1301,8 +1301,7 @@ 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/kernel/cgroup.c b/kernel/cgroup.c
index 2731d11..5ae71d6 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1697,7 +1697,6 @@ 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) {
@@ -1723,7 +1722,6 @@ 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;
@@ -4813,8 +4811,7 @@ unsigned short css_id(struct cgroup_subsys_state *css)
* on this or this is under rcu_read_lock(). Once css->id is allocated,
* it's unchanged until freed.
*/
- cssid = rcu_dereference_check(css->id,
- rcu_read_lock_held() || atomic_read(&css->refcnt));
+ cssid = rcu_dereference_check(css->id, atomic_read(&css->refcnt));

if (cssid)
return cssid->id;
@@ -4826,8 +4823,7 @@ 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));
+ cssid = rcu_dereference_check(css->id, atomic_read(&css->refcnt));

if (cssid)
return cssid->depth;
diff --git a/kernel/exit.c b/kernel/exit.c
index f2b321b..14c9b63 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 57a8346..e432057 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -405,7 +405,6 @@ 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 2e138db..ced7210 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -941,7 +941,6 @@ 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));
@@ -1002,7 +1001,6 @@ 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/kernel/sched.c b/kernel/sched.c
index 9769c75..ad8ab90 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -581,7 +581,6 @@ static inline int cpu_of(struct rq *rq)

#define rcu_dereference_check_sched_domain(p) \
rcu_dereference_check((p), \
- rcu_read_lock_held() || \
lockdep_is_held(&sched_domains_mutex))

/*
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index b83870b..3db78b6 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -97,7 +97,6 @@ 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) {
@@ -105,7 +104,6 @@ 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));
}
@@ -123,7 +121,6 @@ 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) {
@@ -132,7 +129,6 @@ 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 de0d8e4..2aa975e 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 9c38658..3de3768 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;

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index a06ffab..30e242f 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -155,7 +155,6 @@ 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--)
--
1.7.5.4
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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