[PATCH] taskstats: kill ->taskstats_lock in favor of ->siglock

signal_struct is (mostly) protected by ->sighand->siglock, I think we don't
need ->taskstats_lock to protect ->stats.  This also allows us to simplify the
locking in fill_tgid().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 7 insertions, 11 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 213326609bac..3da978eec791 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -830,7 +830,7 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
         if (clone_flags & CLONE_THREAD) {
                 atomic_inc(&current->signal->count);
                 atomic_inc(&current->signal->live);
-                taskstats_tgid_alloc(current->signal);
+                taskstats_tgid_alloc(current);
                 return 0;
         }
         sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 9aeee511a463..b2efda94615a 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -241,11 +241,11 @@ static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk,
         tsk = first;
         read_lock(&tasklist_lock);
         /* Start with stats from dead tasks */
-        if (first->signal) {
-                spin_lock_irqsave(&first->signal->stats_lock, flags);
+        if (first->sighand) {
+                spin_lock_irqsave(&first->sighand->siglock, flags);
                 if (first->signal->stats)
                         memcpy(stats, first->signal->stats, sizeof(*stats));
-                spin_unlock_irqrestore(&first->signal->stats_lock, flags);
+                spin_unlock_irqrestore(&first->sighand->siglock, flags);
         }
 
         do {
@@ -276,7 +276,7 @@ static void fill_tgid_exit(struct task_struct *tsk)
 {
         unsigned long flags;
 
-        spin_lock_irqsave(&tsk->signal->stats_lock, flags);
+        spin_lock_irqsave(&tsk->sighand->siglock, flags);
         if (!tsk->signal->stats)
                 goto ret;
 
@@ -288,7 +288,7 @@ static void fill_tgid_exit(struct task_struct *tsk)
          */
         delayacct_add_tsk(tsk->signal->stats, tsk);
 ret:
-        spin_unlock_irqrestore(&tsk->signal->stats_lock, flags);
+        spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
         return;
 }
 
@@ -464,15 +464,10 @@ void taskstats_exit_send(struct task_struct *tsk, struct taskstats *tidstats,
         size_t size;
         int is_thread_group;
         struct nlattr *na;
-        unsigned long flags;
 
         if (!family_registered || !tidstats)
                 return;
 
-        spin_lock_irqsave(&tsk->signal->stats_lock, flags);
-        is_thread_group = tsk->signal->stats ? 1 : 0;
-        spin_unlock_irqrestore(&tsk->signal->stats_lock, flags);
-
         rc = 0;
         /*
          * Size includes space for nested attributes
@@ -480,6 +475,7 @@ void taskstats_exit_send(struct task_struct *tsk, struct taskstats *tidstats,
         size = nla_total_size(sizeof(u32)) +
                 nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);
 
+        is_thread_group = (tsk->signal->stats != NULL);
         if (is_thread_group)
                 size = 2 * size;        /* PID + STATS + TGID + STATS */