[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>

2 files changed, 1 insertions, 10 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 71c9be59c9c2..1c8d7b5d7a14 100644
--- 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 a28840b11b89..bb63fa1d34a2 100644
--- 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);
         }