Oleg Nesterov wrote:
> 1. ts = timespec_sub(uptime, current->group_leader->start_time);
>
> It is possible that current != tsk. Probably it was supposed
> to be 'tsk->group_leader->start_time. But why we are reading
> group_leader's start_time ? This accounting is per thread,
> not per procees, I changed this to 'tsk->start_time.
> Please corect me.
This is right. Thanks!
>
> 2. stats->ac_ppid = (tsk->parent) ? tsk->parent->pid : 0;
>
> tsk->parent never == NULL, and it is unsafe to dereference it.
> Both the task and it's parent may exit after the caller unlocks
> tasklist_lock, the memory could be unmapped (DEBUG_SLAB).
> (And we should use ->real_parent->tgid in fact).
>
> Q: I don't understand the 'if (thread_group_leader(tsk))' check.
> Why it is needed ?
The code was borrowed from kernel/acct.c. The CSA code was extended
from the BSD accounting, so we just borrowed the basic accounting
stuff from the code.
Thanks,
- jay
>
> Signed-off-by: Oleg Nesterov <[email protected]>
>
> --- STATS/kernel/tsacct.c~2_par_fix 2006-10-22 18:24:03.000000000 +0400
> +++ STATS/kernel/tsacct.c 2006-10-27 01:03:26.000000000 +0400
> @@ -36,7 +36,7 @@ void bacct_add_tsk(struct taskstats *sta
>
> /* calculate task elapsed time in timespec */
> do_posix_clock_monotonic_gettime(&uptime);
> - ts = timespec_sub(uptime, current->group_leader->start_time);
> + ts = timespec_sub(uptime, tsk->start_time);
> /* rebase elapsed time to usec */
> ac_etime = timespec_to_ns(&ts);
> do_div(ac_etime, NSEC_PER_USEC);
> @@ -58,7 +58,10 @@ void bacct_add_tsk(struct taskstats *sta
> stats->ac_uid = tsk->uid;
> stats->ac_gid = tsk->gid;
> stats->ac_pid = tsk->pid;
> - stats->ac_ppid = (tsk->parent) ? tsk->parent->pid : 0;
> + rcu_read_lock();
> + stats->ac_ppid = pid_alive(tsk) ?
> + rcu_dereference(tsk->real_parent)->tgid : 0;
> + rcu_read_unlock();
> stats->ac_utime = cputime_to_msecs(tsk->utime) * USEC_PER_MSEC;
> stats->ac_stime = cputime_to_msecs(tsk->stime) * USEC_PER_MSEC;
> stats->ac_minflt = tsk->min_flt;
>
-
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