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exit: Always reap resource stats in __exit_signal()

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Oleg pointed out that wait_task_zombie adds a task's usage statistics
to the parent's signal struct, but the task's own signal struct should
also propagate the statistics at exit time.

This allows thread_group_cputime(reaped_zombie) to get the statistics
after __unhash_process() has made the task invisible to for_each_thread,
but before the thread has actually been rcu freed, making sure no
non-monotonic results are returned inside that window.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Guillaume Morin <guillaume@morinfr.org>
Cc: Ionut Alexa <ionut.m.alexa@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Michal Schmidt <mschmidt@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: umgwanakikbuti@gmail.com
Cc: fweisbec@gmail.com
Cc: srao@redhat.com
Cc: lwoodman@redhat.com
Cc: atheurer@redhat.com
Link: http://lkml.kernel.org/r/1408133138-22048-2-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Rik van Riel 2014-08-15 16:05:36 -04:00 committed by Ingo Molnar
parent e2627dce26
commit 90ed9cbe76
1 changed files with 21 additions and 22 deletions
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19
kernel/exit.c
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@ -115,15 +115,16 @@ static void __exit_signal(struct task_struct *tsk)
if (tsk == sig->curr_target)
sig->curr_target = next_thread(tsk);
}
/*
* Accumulate here the counters for all threads but the
* group leader as they die, so they can be added into
* the process-wide totals when those are taken.
* The group leader stays around as a zombie as long
* as there are other threads. When it gets reaped,
* the exit.c code will add its counts into these totals.
* We won't ever get here for the group leader, since it
* will have been the last reference on the signal_struct.
* Accumulate here the counters for all threads but the group leader
* as they die, so they can be added into the process-wide totals
* when those are taken. The group leader stays around as a zombie as
* long as there are other threads. When it gets reaped, the exit.c
* code will add its counts into these totals. We won't ever get here
* for the group leader, since it will have been the last reference on
* the signal_struct.
*/
task_cputime(tsk, &utime, &stime);
sig->utime += utime;
@ -137,8 +138,6 @@ static void __exit_signal(struct task_struct *tsk)
sig->oublock += task_io_get_oublock(tsk);
task_io_accounting_add(&sig->ioac, &tsk->ioac);
sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
}
sig->nr_threads--;
__unhash_process(tsk, group_dead);