Oleg Nesterov <[email protected]> writes:
> On 09/10, Eric W. Biederman wrote:
>>
>> Ok. I think I see the where the confusion is. We were looking
>> at different parts of the puzzle. But I we need to resolve this
>> to make certain I didn't do something clever and racy.
>
> Yes, I think we misunderstood each other :)
>
>> As for the rest of your suggestion it would not be hard to be able to
>> follow a struct pid pointer in an rcu safe way, and we do in the pid
>> hash table. In other contexts so far I always have other variables
>> that need to be updated in concert, so there isn't a point in coming
>> up with a lockless implementation. I believe vt_pid is the only
>> case that I have run across where this is a problem and I have
>> at least preliminary patches for every place where signals are
>> sent.
>>
>> Updating this old code is painful.
>
> No, no, we shouldn't change the old code, it is fine.
>
So what happens when:
cpu0: cpu1:
kill_pid(vt_pid,....) fn_SAK()->vc_reset()->put_pid(xchg(&vt_pid, NULL))
Can't kill_pid dereference vt_pid after put_pid is called?
It's a microscopic window, and requires the user to attempt a vt switch
and a sak simultaneously but I think it is there.
Eric
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