Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 28 May 2008 08:03:08 -0700 | Subject | Re: [PATCH] kill_something_info: don't take tasklist_lock for pid==-1 case |
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Atsushi TSUJI <a-tsuji@bk.jp.nec.com> writes:
>> Call me paranoid but I don't think there is any guarantee without a lock >> that we will hit the -ERESTARTNOITR check for new processes. I think we >> have a slight race where the fork process may not have received the signal >> (because it is near the tail of the list) but the new process would be >> added to the list immediately after we read it's pointer. > > I know it might happen some races, but, as Oleg say, it is no problem > on the user side. Users cannot realize whether the process forked > during kill or after. We can pretend it was forked after kill > finished. So I think the change to convert tasklist_lock to > rcu_read_lock is reasonable way to avoid the local DOS for kill(-1,sig) case.
We can only pretend that if the parent lives. If the parent is killed then we can not so pretend.
Which in a lot of ways is the problem. kill(-1,SIGKIL) should kill everything except for init and the process that sent the signal. If anything else survives we have a broken the shutdown scripts.
Since the race would rarely hit it will take ages for someone to trace back to a kernel change.
If I could convince myself that Oleg is correct and that what Oleg is proposing will always work I don't have a problem.
Eric
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