On Fri 09-04-21 13:09:57, Mel Gorman wrote: > zone_pcp_reset allegedly protects against a race with drain_pages > using local_irq_save but this is bogus. local_irq_save only operates > on the local CPU. If memory hotplug is running on CPU A and drain_pages > is running on CPU B, disabling IRQs on CPU A does not affect CPU B and > offers no protection. Yes, the synchronization aspect is bogus indeed. > This patch reorders memory hotremove such that the PCP structures > relevant to the zone are no longer reachable by the time the structures > are freed. With this reordering, no protection is required to prevent > a use-after-free and the IRQs can be left enabled. zone_pcp_reset is > renamed to zone_pcp_destroy to make it clear that the per-cpu structures > are deleted when the function returns. Wouldn't it be much easier to simply not destroy/reset pcp of an empty zone at all? The whole point of this exercise seems to be described in 340175b7d14d5. setup_zone_pageset can check for an already allocated pcp and simply reinitialize it. -- Michal Hocko SUSE Labs
