--- Andi Kleen <[email protected]> wrote:
> On Sun, Aug 12, 2007 at 10:48:05AM -0700, Casey Schaufler wrote:
> >
> > --- Andi Kleen <[email protected]> wrote:
> >
> > > > Entries are never deleted, although they can be modified.
> > >
> > > The modification case still seems racy then.
> >
> > Fair enough. I'll look into real list management.
>
> You don't necessarily need more list management if you don't
> plan to remove entries, but just replace them.
>
> e.g. what could work to atomically replace is:
>
> - Make the buffer a pointer to an allocated buffer that also
> contains a struct rcu_head.
> - Reader: Does rcu_read_lock() around list walk (that just disables
> preemption on preemptible kernels and is otherwise a nop).
> Also uses rcu_reference for reading the pointer.
> - Writer: Continues using the mutex to protect against other writers.
> When changing an entry allocate a new buffer + rcu_head. Initialize
> buffer. Replace pointer. Free old buffer using call_rcu()
>
> The RCU would just make sure the buffer is not freed while other
> CPUs are still accessing it. It also means they can use stale
> rules for a time, but it is a strictly bounded time
> (bounded to max time walking the list plus max time any interrupt
> handlers inbetween run [admittedly that can be very long in theory,
> but it's all logically only a single rule check])
Thank you. You have no idea how helpful that little suggestion was.
Casey Schaufler
[email protected]
-
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]
