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.
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 ?
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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