On 04/12, Srivatsa Vaddagiri wrote:
>
> On Tue, Apr 03, 2007 at 10:48:20PM +0530, Srivatsa Vaddagiri wrote:
> > > Actually, we should do this before destroy_workqueue() calls
> > > flush_workqueue().
> > > Otherwise flush_cpu_workqueue() can hang forever in a similar manner.
> >
> > Yep. I guess these are a class of freezer deadlocks very similar to vfork
> > parent waiting on child case. I get a feeling these should become common
> > outside of kthread too (A waits on B for something, B gets frozen, which
> > means A won't freeze causing freezer to fail). Can freezer detect this
> > dependency somehow and thaw B automatically? Probably not that easy ..
>
> I wonder if there is some value in "enforcing" an order in which
> processes get frozen i.e freeze A first before B. That may solve the
> deadlocks we have been discussing wrt kthread_stop and flush_workqueue
> as well.
Perhaps we can add "atomic_t xxx" to task_struct.
int freezing(struct task_struct *p)
{
return test_tsk_thread_flag(p, TIF_FREEZE)
&& atomic_read(&p->xxx) == 0;
}
void xxx_start(struct task_struct *p)
{
atomic_inc(p->xxx);
thaw_process(p);
}
xxx_end(struct task_struct *p)
{
atomic_dec(p->xxx);
}
Now,
xxx_start(p);
... wait for something which depends on p...
xxx_end(p);
Of course we need other changes, freeze_process() should check ->xxx, etc.
I am not sure this makes sense.
Oleg.
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