Messages in this thread | | | From | Roland McGrath <> | Subject | Re: [PATCH 2/2] posix-cpu-timers: use ->sighand instead of ->signal to check the task is alive | Date | Thu, 5 Feb 2009 12:45:21 -0800 (PST) |
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> We can't use them as refcounts. You can't bump ->live or ->count without > breaking group_dead or exec logic. Perhaps we can use ->count, but then > we need other changes.
We certainly need to clean up exec anyway.
> But this has nothing to do with this patch.
Agreed.
> The goal is to keep task->signal after release_task(), it will be freed > by __put_task_struct(). This allows a lot of simplifications and we can > move some fields from task_struct to signal_struct.
That sounds fine to me in theory, but I still wonder what the story will be about the use of siglock.
> But first we should change the code which does [...]
I did understand the rationale given the signal_struct lifetime change.
> > Uses here protecting cpu_clock_sample_group() e.g., are > > around looking at ->signal->foobar, so if ->signal is still there, why not > > look at it and be able to get the sample in whatever small window this is? > > What if arm_timer() sees ->signal != NULL, proceeds, and attaches the > timer to the signal_struct of the already dead task? This signal_strcut > will be released with the pending timer.
Of course. I distinctly mentioned the read-only uses (sample).
> Even cpu_clock_sample_group() is not safe, unless we add other changes.
Why? It does no locking and only relies on the signal_struct lifetime.
> But in any case. Even if we don't need the further changes, do you > agree this patch is correct and doesn't change the behaviour?
Yes.
Thanks, Roland
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