Hi Luca,
On 11/02/2022 15:00, Luca Fancellu wrote:
pend_lpi_tree is a radix tree used to store pending irqs, the tree is
protected by a lock for read/write operations.
Currently the radix tree default function to free items uses the
RCU mechanism, calling call_rcu and deferring the operation.
However every access to the structure is protected by the lock so we
can avoid using the default free function that, by using RCU,
increases memory usage and impacts the predictability of the system.
I understand goal but looking at the implementation of
vgic_v3_lpi_to_pending() (Copied below for convenience). We would
release the lock as soon as the look-up finish, yet the element is returned.
static struct pending_irq *vgic_v3_lpi_to_pending(struct domain *d,
unsigned int lpi)
{
struct pending_irq *pirq;
read_lock(&d->arch.vgic.pend_lpi_tree_lock);
pirq = radix_tree_lookup(&d->arch.vgic.pend_lpi_tree, lpi);
read_unlock(&d->arch.vgic.pend_lpi_tree_lock);
return pirq;
}
So the lock will not protect us against removal. If you want to drop the
RCU, you will need to ensure the structure pending_irq is suitably
protected. I haven't check whether there are other locks that may suit
us here.
Cheers,
--
Julien Grall
