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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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