On Tue, 1 Nov 2005, Chandra Seetharaman wrote:
> > Register and unregister will continue to work as before, requiring a
> > process context and the ability to sleep. notifier_block_enable/disable
> > should be used when:
> >
> > a callout wants to disable itself as it is running, or
> >
> > someone running in an atomic context wants to enable or disable
> > a callout.
> >
> > In the first case, unregister can't be used because it would hang. In the
> > second case, register/unregister can't be used because they need to be
> > able to sleep.
> >
> > In both cases the notifier block would have to be registered beforehand
> > and unregistered later.
>
> I understand. Thanks for the explanation. I like the option below better
> (no new interface).
You mean the RCU-style update? It will hang when a callout routine tries
to deregister itself as it is running, although we could add a new
unregister_self API to handle that. Just check for num_callers equal to 1
instead of 0.
> > No; the list _won't_ be protected in call_chain. It will be possible to
> > unregister a callout while the chain is in use. That's how the RCU
> > approach works -- it uses no read locks, only write locks.
>
> but, list_del poisons the next pointer which is not good for a reader
> that is walking through the list, we have to use list_del_rcu instead.
Agreed.
> Also, do you think we have to use _rcu versions of list traversal
> functions in call_chain ?
Yes.
Note that on an SMP system you run the risk of starvation (the chain gets
called so frequently that it's _always_ running on some CPU). We can
probably ignore that possibility.
Would you like to code up these ideas?
Alan Stern
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
