[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>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 71c9be5..1c8d7b5 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -261,7 +261,6 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
        sigemptyset(&ignored);
        sigemptyset(&caught);
 
-       rcu_read_lock();
        if (lock_task_sighand(p, &flags)) {
                pending = p->pending.signal;
                shpending = p->signal->shared_pending.signal;
@@ -272,7 +271,6 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
                qlim = p->signal->rlim[RLIMIT_SIGPENDING].rlim_cur;
                unlock_task_sighand(p, &flags);
        }
-       rcu_read_unlock();
 
        seq_printf(m, "Threads:\t%d\n", num_threads);
        seq_printf(m, "SigQ:\t%lu/%lu\n", qsize, qlim);

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a28840b..bb63fa1 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -164,7 +164,6 @@ static struct fs_struct *get_fs_struct(struct task_struct *task)
 
 static int get_nr_threads(struct task_struct *tsk)
 {
-       /* Must be called with the rcu_read_lock held */
        unsigned long flags;
        int count = 0;
 
@@ -471,14 +470,10 @@ static int proc_pid_limits(struct task_struct *task, char *buffer)
 
        struct rlimit rlim[RLIM_NLIMITS];
 
-       rcu_read_lock();
-       if (!lock_task_sighand(task,&flags)) {
-               rcu_read_unlock();
+       if (!lock_task_sighand(task, &flags))
                return 0;
-       }
        memcpy(rlim, task->signal->rlim, sizeof(struct rlimit) * RLIM_NLIMITS);
        unlock_task_sighand(task, &flags);
-       rcu_read_unlock();
 
        /*
         * print the file header
@@ -3088,9 +3083,7 @@ static int proc_task_getattr(struct vfsmount *mnt, struct dentry *dentry, struct
        generic_fillattr(inode, stat);
 
        if (p) {
-               rcu_read_lock();
                stat->nlink += get_nr_threads(p);
-               rcu_read_unlock();
                put_task_struct(p);
        }
 

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index bbe6b31..ad958c1 100644 (file)
--- 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,