[PATCH] signal, procfs: some lock_task_sighand() users do not need rcu_read_lock()

lock_task_sighand() make sure task->sighand is being protected,
so we do not need rcu_read_lock().
[ exec() will get task->sighand->siglock before change task->sighand! ]

But code using rcu_read_lock() _just_ to protect lock_task_sighand()
only appear in procfs. (and some code in procfs use lock_task_sighand()
without such redundant protection.)

Other subsystem may put lock_task_sighand() into rcu_read_lock()
critical region, but these rcu_read_lock() are used for protecting
"for_each_process()", "find_task_by_vpid()" etc. , not for protecting
lock_task_sighand().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
[ok from Oleg]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

1 files changed, 0 insertions, 2 deletions

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index bbe6b31c3c56..ad958c1ec708 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -333,12 +333,10 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
         unsigned long flags;
         int num_threads = 1;
 
-        rcu_read_lock();
         if (lock_task_sighand(p, &flags)) {
                 num_threads = atomic_read(&p->signal->count);
                 unlock_task_sighand(p, &flags);
         }
-        rcu_read_unlock();
 
         SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, p->pid, num_threads);
         SEQ_printf(m,