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