[RFC,PATCH 2/2] cputimers/proc: do_task_stat()->thread_group_times() is racy and O(n) under ->siglock
in [Kernel]
|
Prev: [RFC,PATCH 1/2] cputimers/proc: do_task_stat()->task_times() can race with getrusage()
Next: cputimers/proc: do_task_stat()->thread_group_times() is racy and O(n) under ->siglock
From: Oleg Nesterov on 24 Mar 2010 16:50 Nowadays ->siglock is overloaded, it would be really nice to change do_task_stat() to walk through the list of threads lockless. And note that we are doing while_each_thread() twice! while_each_thread() is rcu-safe, but thread_group_times() also needs ->siglock to serialize the modifications of signal_struct->prev_Xtime members. (however, please note that currently do_task_stat() can race with wait_task_zombie() which calls thread_group_times() without siglock). This patch changes the code back to use thread_group_cputime(), as we did before 0cf55e1e "sched, cputime: Introduce thread_group_times()". Of course, this makes the output from /proc/pid/stat less accurate, but otoh this allows us to make do_task_stat() (apart from ->tty bits). Signed-off-by: Oleg Nesterov <oleg(a)redhat.com> --- fs/proc/array.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- 34-rc1/fs/proc/array.c~PROC_5_DTS_TGTS_IS_PITA 2010-03-24 20:47:19.000000000 +0100 +++ 34-rc1/fs/proc/array.c 2010-03-24 20:47:51.000000000 +0100 @@ -403,6 +403,7 @@ static int do_task_stat(struct seq_file if (lock_task_sighand(task, &flags)) { struct signal_struct *sig = task->signal; + struct task_cputime cputime; if (sig->tty) { struct pid *pgrp = tty_get_pgrp(sig->tty); @@ -433,8 +434,11 @@ static int do_task_stat(struct seq_file min_flt += sig->min_flt; maj_flt += sig->maj_flt; - thread_group_times(task, &utime, &stime); + gtime = cputime_add(gtime, sig->gtime); + thread_group_cputime(task, &cputime); + utime = cputime.utime; + stime = cputime.stime; } sid = task_session_nr_ns(task, ns); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |