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Date: Fri, 27 Oct 2006 03:22:24 +0400 From: Oleg Nesterov <oleg@...sign.ru> To: Andrew Morton <akpm@...l.org> Cc: Shailabh Nagar <nagar@...son.ibm.com>, Balbir Singh <balbir@...ibm.com>, Jay Lan <jlan@....com>, linux-kernel@...r.kernel.org Subject: [PATCH 6/6] taskstats: don't use tasklist_lock Remove tasklist_lock from taskstats.c. find_task_by_pid() is rcu-safe. ->siglock allows us to traverse subthread without tasklist. Q: delay accounting looks wrong to me. If sub-thread has already called taskstats_exit_send() but didn't call release_task(self) yet it will be accounted twice. The window is big. No? Signed-off-by: Oleg Nesterov <oleg@...sign.ru> --- STATS/kernel/taskstats.c~6_tasklist 2006-10-27 02:00:32.000000000 +0400 +++ STATS/kernel/taskstats.c 2006-10-27 03:03:40.000000000 +0400 @@ -174,21 +174,19 @@ static void send_cpu_listeners(struct sk up_write(&listeners->sem); } -static int fill_pid(pid_t pid, struct task_struct *pidtsk, +static int fill_pid(pid_t pid, struct task_struct *tsk, struct taskstats *stats) { int rc = 0; - struct task_struct *tsk = pidtsk; - if (!pidtsk) { - read_lock(&tasklist_lock); + if (!tsk) { + rcu_read_lock(); tsk = find_task_by_pid(pid); - if (!tsk) { - read_unlock(&tasklist_lock); + if (tsk) + get_task_struct(tsk); + rcu_read_unlock(); + if (!tsk) return -ESRCH; - } - get_task_struct(tsk); - read_unlock(&tasklist_lock); } else get_task_struct(tsk); @@ -214,40 +212,28 @@ static int fill_pid(pid_t pid, struct ta } -static int fill_tgid(pid_t tgid, struct task_struct *tgidtsk, +static int fill_tgid(pid_t tgid, struct task_struct *first, struct taskstats *stats) { - struct task_struct *tsk, *first; + struct task_struct *tsk; unsigned long flags; + int rc = -ESRCH; /* * Add additional stats from live tasks except zombie thread group * leaders who are already counted with the dead tasks */ - first = tgidtsk; - if (!first) { - read_lock(&tasklist_lock); + rcu_read_lock(); + if (!first) first = find_task_by_pid(tgid); - if (!first) { - read_unlock(&tasklist_lock); - return -ESRCH; - } - get_task_struct(first); - read_unlock(&tasklist_lock); - } else - get_task_struct(first); + if (!first || !lock_task_sighand(first, &flags)) + goto out; - tsk = first; - read_lock(&tasklist_lock); - /* Start with stats from dead tasks */ - 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->sighand->siglock, flags); - } + if (first->signal->stats) + memcpy(stats, first->signal->stats, sizeof(*stats)); + tsk = first; do { if (tsk->exit_state == EXIT_ZOMBIE && thread_group_leader(tsk)) continue; @@ -260,15 +246,18 @@ static int fill_tgid(pid_t tgid, struct delayacct_add_tsk(stats, tsk); } while_each_thread(first, tsk); - read_unlock(&tasklist_lock); - stats->version = TASKSTATS_VERSION; + unlock_task_sighand(first, &flags); + rc = 0; +out: + rcu_read_unlock(); + + stats->version = TASKSTATS_VERSION; /* * Accounting subsytems can also add calls here to modify * fields of taskstats. */ - put_task_struct(first); - return 0; + return rc; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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