On 26.03.21 02:20, Alistair Popple wrote:
request_free_mem_region() is used to find an empty range of physical addresses for hotplugging ZONE_DEVICE memory. It does this by iterating over the range of possible addresses using region_intersects() to see if the range is free.
Just a high-level question: how does this iteract with memory hot(un)plug? IOW, how defines and manages the "range of possible addresses" ?
region_intersects() obtains a read lock before walking the resource tree to protect against concurrent changes. However it drops the lock prior to returning. This means by the time request_mem_region() is called in request_free_mem_region() another thread may have already reserved the requested region resulting in unexpected failures and a message in the kernel log from hitting this condition:
I am confused. Why can't we return an error to the caller and let the caller continue searching? This feels much simpler than what you propose here. What am I missing?
-- Thanks, David / dhildenb
