On Fri, Oct 09, 2020 at 03:28:54PM +0300, Pavel Begunkov wrote: > On 09/10/2020 15:12, Matthew Wilcox wrote: > >> It seems this fails on "node->shift" in xas_next_entry(), that would > >> mean that the node itself was freed while we're iterating on it. > >> > >> __io_uring_files_cancel() iterates with xas_next_entry() and creates > >> XA_STATE once by hand, but it also removes entries in the loop with > >> io_uring_del_task_file() -> xas_store(&xas, NULL); without updating > >> the iterating XA_STATE. Could it be the problem? See a diff below > > > > No, the problem is that the lock is dropped after calling > > xas_next_entry(), and at any point after calling xas_next_entry(), > > the node that it's pointing to can be freed. > > Only the task itself clears/removes entries, others can only insert. > So, could it be freed even though there are no parallel erases? Not with today's implementation, but that's something that might change in the future. I agree it's probably the task itself that's deleting the entry and causing the node to be deleted.
