Messages in this thread Patch in this message | | | Date | Mon, 29 Mar 2010 20:12:38 +0200 | From | Oleg Nesterov <> | Subject | [PATCH -mm 1/4] cputimers: thread_group_cputime: cleanup rcu/signal stuff |
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- With the recent changes 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().
- Change the main loop to use the while_each_thread() helper.
This change itself doesn't add the functional changes, currently it is always called under tasklist/siglock or when we know that this thread group is already dead (wait, coredump).
Signed-off-by: Oleg Nesterov <oleg@redhat.com> ---
kernel/posix-cpu-timers.c | 21 +++++++-------------- 1 file changed, 7 insertions(+), 14 deletions(-)
--- 34-rc1/kernel/posix-cpu-timers.c~cpuacct_1_thread_group_cputime_cleanup_rcu 2010-03-29 18:08:14.000000000 +0200 +++ 34-rc1/kernel/posix-cpu-timers.c 2010-03-29 18:09:15.000000000 +0200 @@ -233,31 +233,24 @@ static int cpu_clock_sample(const clocki void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times) { - struct sighand_struct *sighand; - struct signal_struct *sig; + struct signal_struct *sig = tsk->signal; struct task_struct *t; - *times = INIT_CPUTIME; + times->utime = sig->utime; + times->stime = sig->stime; + times->sum_exec_runtime = sig->sum_sched_runtime; rcu_read_lock(); - sighand = rcu_dereference(tsk->sighand); - if (!sighand) + /* make sure we can trust tsk->thread_group list */ + if (!likely(pid_alive(tsk))) goto out; - sig = tsk->signal; - t = tsk; do { times->utime = cputime_add(times->utime, t->utime); times->stime = cputime_add(times->stime, t->stime); times->sum_exec_runtime += t->se.sum_exec_runtime; - - t = next_thread(t); - } while (t != tsk); - - times->utime = cputime_add(times->utime, sig->utime); - times->stime = cputime_add(times->stime, sig->stime); - times->sum_exec_runtime += sig->sum_sched_runtime; + } while_each_thread(tsk, t); out: rcu_read_unlock(); }
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