This patch reverts 'CONFIG_SMP && thread_group_empty()'
optimization in sys_times(). The reason is that the next
patch breaks memory ordering which is needed for that
optimization.
tasklist_lock in sys_times() will be eliminated completely
by further patch.
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.16-rc3/kernel/exit.c~2_REVERT 2006-02-23 00:32:46.000000000 +0300
+++ 2.6.16-rc3/kernel/exit.c 2006-02-23 00:54:28.000000000 +0300
@@ -137,11 +137,7 @@ repeat:
ptrace_unlink(p);
BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
__exit_signal(p);
- /*
- * Note that the fastpath in sys_times depends on __exit_signal having
- * updated the counters before a task is removed from the tasklist of
- * the process by __unhash_process.
- */
+
__unhash_process(p);
/*
--- 2.6.16-rc3/kernel/sys.c~2_REVERT 2006-02-13 21:47:19.000000000 +0300
+++ 2.6.16-rc3/kernel/sys.c 2006-02-23 00:55:56.000000000 +0300
@@ -1009,69 +1009,35 @@ asmlinkage long sys_times(struct tms __u
*/
if (tbuf) {
struct tms tmp;
+ struct task_struct *tsk = current;
+ struct task_struct *t;
cputime_t utime, stime, cutime, cstime;
-#ifdef CONFIG_SMP
- if (thread_group_empty(current)) {
- /*
- * Single thread case without the use of any locks.
- *
- * We may race with release_task if two threads are
- * executing. However, release task first adds up the
- * counters (__exit_signal) before removing the task
- * from the process tasklist (__unhash_process).
- * __exit_signal also acquires and releases the
- * siglock which results in the proper memory ordering
- * so that the list modifications are always visible
- * after the counters have been updated.
- *
- * If the counters have been updated by the second thread
- * but the thread has not yet been removed from the list
- * then the other branch will be executing which will
- * block on tasklist_lock until the exit handling of the
- * other task is finished.
- *
- * This also implies that the sighand->siglock cannot
- * be held by another processor. So we can also
- * skip acquiring that lock.
- */
- utime = cputime_add(current->signal->utime, current->utime);
- stime = cputime_add(current->signal->utime, current->stime);
- cutime = current->signal->cutime;
- cstime = current->signal->cstime;
- } else
-#endif
- {
-
- /* Process with multiple threads */
- struct task_struct *tsk = current;
- struct task_struct *t;
+ read_lock(&tasklist_lock);
+ utime = tsk->signal->utime;
+ stime = tsk->signal->stime;
+ t = tsk;
+ do {
+ utime = cputime_add(utime, t->utime);
+ stime = cputime_add(stime, t->stime);
+ t = next_thread(t);
+ } while (t != tsk);
- read_lock(&tasklist_lock);
- utime = tsk->signal->utime;
- stime = tsk->signal->stime;
- t = tsk;
- do {
- utime = cputime_add(utime, t->utime);
- stime = cputime_add(stime, t->stime);
- t = next_thread(t);
- } while (t != tsk);
+ /*
+ * While we have tasklist_lock read-locked, no dying thread
+ * can be updating current->signal->[us]time. Instead,
+ * we got their counts included in the live thread loop.
+ * However, another thread can come in right now and
+ * do a wait call that updates current->signal->c[us]time.
+ * To make sure we always see that pair updated atomically,
+ * we take the siglock around fetching them.
+ */
+ spin_lock_irq(&tsk->sighand->siglock);
+ cutime = tsk->signal->cutime;
+ cstime = tsk->signal->cstime;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ read_unlock(&tasklist_lock);
- /*
- * While we have tasklist_lock read-locked, no dying thread
- * can be updating current->signal->[us]time. Instead,
- * we got their counts included in the live thread loop.
- * However, another thread can come in right now and
- * do a wait call that updates current->signal->c[us]time.
- * To make sure we always see that pair updated atomically,
- * we take the siglock around fetching them.
- */
- spin_lock_irq(&tsk->sighand->siglock);
- cutime = tsk->signal->cutime;
- cstime = tsk->signal->cstime;
- spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
- }
tmp.tms_utime = cputime_to_clock_t(utime);
tmp.tms_stime = cputime_to_clock_t(stime);
tmp.tms_cutime = cputime_to_clock_t(cutime);
-
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