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author | Oleg Nesterov <oleg@redhat.com> | 2010-06-11 01:09:56 +0200 |
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committer | Ingo Molnar <mingo@elte.hu> | 2010-06-18 10:46:56 +0200 |
commit | bfac7009180901f57f20a73c53c3e57b1ce75a1b (patch) | |
tree | f167c0a6bfbf397ad668517bdccbc9d0de162715 /kernel/posix-cpu-timers.c | |
parent | 48286d5088a3ba76de40a6b70221632a49cab7a1 (diff) | |
download | linux-stable-bfac7009180901f57f20a73c53c3e57b1ce75a1b.tar.gz linux-stable-bfac7009180901f57f20a73c53c3e57b1ce75a1b.tar.bz2 linux-stable-bfac7009180901f57f20a73c53c3e57b1ce75a1b.zip |
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 <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100610230956.GA25921@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/posix-cpu-timers.c')
-rw-r--r-- | kernel/posix-cpu-timers.c | 21 |
1 files changed, 7 insertions, 14 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 9829646d399c..bf2a6502860a 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -232,31 +232,24 @@ static int cpu_clock_sample(const clockid_t which_clock, struct task_struct *p, 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(); } |