From: Oleg Nesterov Date: Thu, 10 Jun 2010 23:09:56 +0000 (+0200) Subject: sched: thread_group_cputime: Simplify, document the "alive" check X-Git-Tag: v2.6.36-rc1~531^2~10 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bfac7009180901f57f20a73c53c3e57b1ce75a1b;p=pandora-kernel.git sched: thread_group_cputime: Simplify, document the "alive" check thread_group_cputime() looks as if it is rcu-safe, but in fact this was wrong until ea6d290c which pins task->signal to task_struct. It checks ->sighand != NULL under rcu, but this can't help if ->signal can go away. Fortunately the caller either holds ->siglock, or it is fastpath_timer_check() which uses current and checks exit_state == 0. - Since ea6d290c commit tsk->signal is stable, we can read it first and avoid the initialization from INIT_CPUTIME. - Even if tsk->signal is always valid, we still have to check it is safe to use next_thread() under rcu_read_lock(). Currently the code checks ->sighand != NULL, change it to use pid_alive() which is commonly used to ensure the task wasn't unhashed before we take rcu_read_lock(). Add the comment to explain this check. - Change the main loop to use the while_each_thread() helper. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <20100610230956.GA25921@redhat.com> Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed