--- 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/
