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Subject[PATCH tip/core/rcu 5/8] sched: use lockdep-based checking on rcu_dereference()
Date
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Update the rcu_dereference() usages to take advantage of the new
lockdep-based checking.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/cgroup.h | 2 +-
include/linux/cred.h | 2 +-
init/main.c | 2 ++
kernel/exit.c | 14 +++++++++++---
kernel/fork.c | 1 +
kernel/notifier.c | 6 +++---
kernel/pid.c | 2 +-
kernel/sched.c | 6 +++---
8 files changed, 23 insertions(+), 12 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0008dee..d4c95c9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -486,7 +486,7 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
static inline struct cgroup_subsys_state *task_subsys_state(
struct task_struct *task, int subsys_id)
{
- return rcu_dereference(task->cgroups->subsys[subsys_id]);
+ return rcu_dereference_sched(task->cgroups->subsys[subsys_id]);
}

static inline struct cgroup* task_cgroup(struct task_struct *task,
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 4e3387a..4db09f8 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -280,7 +280,7 @@ static inline void put_cred(const struct cred *_cred)
* task or by holding tasklist_lock to prevent it from being unlinked.
*/
#define __task_cred(task) \
- ((const struct cred *)(rcu_dereference((task)->real_cred)))
+ ((const struct cred *)(rcu_dereference_check((task)->real_cred, rcu_read_lock_held() || lockdep_is_held(&tasklist_lock))))

/**
* get_task_cred - Get another task's objective credentials
diff --git a/init/main.c b/init/main.c
index 5988deb..ae2338e 100644
--- a/init/main.c
+++ b/init/main.c
@@ -427,7 +427,9 @@ static noinline void __init_refok rest_init(void)
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
+ rcu_read_lock();
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
+ rcu_read_unlock();
unlock_kernel();

/*
diff --git a/kernel/exit.c b/kernel/exit.c
index e61891f..ddc7cfe 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -84,7 +84,9 @@ static void __exit_signal(struct task_struct *tsk)
BUG_ON(!sig);
BUG_ON(!atomic_read(&sig->count));

- sighand = rcu_dereference(tsk->sighand);
+ sighand = rcu_dereference_check(tsk->sighand,
+ rcu_read_lock_held() ||
+ lock_is_held(&tasklist_lock));
spin_lock(&sighand->siglock);

posix_cpu_timers_exit(tsk);
@@ -169,8 +171,10 @@ void release_task(struct task_struct * p)
repeat:
tracehook_prepare_release_task(p);
/* don't need to get the RCU readlock here - the process is dead and
- * can't be modifying its own credentials */
+ * can't be modifying its own credentials. But shut RCU-lockdep up */
+ rcu_read_lock();
atomic_dec(&__task_cred(p)->user->processes);
+ rcu_read_unlock();

proc_flush_task(p);

@@ -474,9 +478,11 @@ static void close_files(struct files_struct * files)
/*
* It is safe to dereference the fd table without RCU or
* ->file_lock because this is the last reference to the
- * files structure.
+ * files structure. But use RCU to shut RCU-lockdep up.
*/
+ rcu_read_lock();
fdt = files_fdtable(files);
+ rcu_read_unlock();
for (;;) {
unsigned long set;
i = j * __NFDBITS;
@@ -522,10 +528,12 @@ void put_files_struct(struct files_struct *files)
* at the end of the RCU grace period. Otherwise,
* you can free files immediately.
*/
+ rcu_read_lock();
fdt = files_fdtable(files);
if (fdt != &files->fdtab)
kmem_cache_free(files_cachep, files);
free_fdtable(fdt);
+ rcu_read_unlock();
}
}

diff --git a/kernel/fork.c b/kernel/fork.c
index 4c20fff..545e024 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -85,6 +85,7 @@ int max_threads; /* tunable limit on nr_threads */
DEFINE_PER_CPU(unsigned long, process_counts) = 0;

__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
+EXPORT_SYMBOL_GPL(tasklist_lock);

int nr_processes(void)
{
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 61d5aa5..fea84bc 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -78,10 +78,10 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,
int ret = NOTIFY_DONE;
struct notifier_block *nb, *next_nb;

- nb = rcu_dereference(*nl);
+ nb = rcu_dereference_raw(*nl);

while (nb && nr_to_call) {
- next_nb = rcu_dereference(nb->next);
+ next_nb = rcu_dereference_raw(nb->next);

#ifdef CONFIG_DEBUG_NOTIFIERS
if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
@@ -309,7 +309,7 @@ int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
* racy then it does not matter what the result of the test
* is, we re-check the list after having taken the lock anyway:
*/
- if (rcu_dereference(nh->head)) {
+ if (rcu_dereference_raw(nh->head)) {
down_read(&nh->rwsem);
ret = notifier_call_chain(&nh->head, val, v, nr_to_call,
nr_calls);
diff --git a/kernel/pid.c b/kernel/pid.c
index d3f722d..3a39e0a 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -367,7 +367,7 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type)
struct task_struct *result = NULL;
if (pid) {
struct hlist_node *first;
- first = rcu_dereference(pid->tasks[type].first);
+ first = rcu_dereference_check(pid->tasks[type].first, rcu_read_lock_held() || lockdep_is_held(&tasklist_lock));
if (first)
result = hlist_entry(first, struct task_struct, pids[(type)].node);
}
diff --git a/kernel/sched.c b/kernel/sched.c
index e69fee4..1fd1c63 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -652,7 +652,7 @@ static inline int cpu_of(struct rq *rq)
* preempt-disabled sections.
*/
#define for_each_domain(cpu, __sd) \
- for (__sd = rcu_dereference(cpu_rq(cpu)->sd); __sd; __sd = __sd->parent)
+ for (__sd = rcu_dereference_sched(cpu_rq(cpu)->sd); __sd; __sd = __sd->parent)

#define cpu_rq(cpu) (&per_cpu(runqueues, (cpu)))
#define this_rq() (&__get_cpu_var(runqueues))
@@ -1528,7 +1528,7 @@ static unsigned long target_load(int cpu, int type)

static struct sched_group *group_of(int cpu)
{
- struct sched_domain *sd = rcu_dereference(cpu_rq(cpu)->sd);
+ struct sched_domain *sd = rcu_dereference_sched(cpu_rq(cpu)->sd);

if (!sd)
return NULL;
@@ -4813,7 +4813,7 @@ static void run_rebalance_domains(struct softirq_action *h)

static inline int on_null_domain(int cpu)
{
- return !rcu_dereference(cpu_rq(cpu)->sd);
+ return !rcu_dereference_sched(cpu_rq(cpu)->sd);
}

/*
--
1.5.2.5


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