On Tue, 2025-01-14 at 18:00 +0100, Michal Hocko wrote: > On Tue 14-01-25 11:51:18, Rik van Riel wrote: > > On Tue, 2025-01-14 at 17:46 +0100, Michal Hocko wrote: > > > On Tue 14-01-25 11:09:55, Johannes Weiner wrote: > > > > > > > charge_memcg > > > > mem_cgroup_swapin_charge_folio > > > > __read_swap_cache_async > > > > swapin_readahead > > > > do_swap_page > > > > handle_mm_fault > > > > do_user_addr_fault > > > > exc_page_fault > > > > asm_exc_page_fault > > > > __get_user > > > > > > All the way here and return the failure to futex_cleanup which > > > doesn't > > > retry __get_user on the failure AFAICS (exit_robust_list). But I > > > might > > > be missing something, it's been quite some time since I've looked > > > into > > > futex code. > > > > Can you explain how -ENOMEM would get propagated down > > past the page fault handler? > > > > This isn't get_user_pages(), which can just pass > > -ENOMEM on to the caller. > > > > If there is code to pass -ENOMEM on past the page > > fault exception handler, I have not been able to > > find it. How does this work? > > This might be me misunderstading get_user machinery but doesn't it > return a failure on PF handler returing ENOMEM? I believe __get_user simply does a memcpy, and ends up in the page fault handler. It does not access userspace explicitly like we do with functions like get_user_pages. -- All Rights Reversed.
