On Tue, Jan 14, 2020 at 01:17:45PM -0500, Waiman Long wrote: > The owner field is just a pointer to the task structure with the lower 3 > bits served as flag bits. Setting owner to RWSEM_OWNER_UNKNOWN (-2) will > stop optimistic spinning. So under what condition did the crash happen? When running xfstests with all patches in this series except for this one, IIRC in generic/114. > Anyway, PeterZ is working on revising the percpu-rwsem implementation to > more gracefully handle the frozen case. At the end, there will not be a > need for the RWSEM_OWNER_UNKNOWN magic and it can be removed. Well, this series relies on that value. And I think it fundamentally is the right thing to do for AIO, and potentially other I/O related locking where we take a lock to synchronize access to data, then do I/O and then eventually get an I/O completion from an interrupt. Even thinking from the PREEMP_RT context we want to boost the initial thread as long as we can, then do nothing when it is off to I/O hardware (except maybe providing good diagnostics that the cause for the latency is I/O), and then boost the thread that is handling the completion. Things like the i_dio_count hack can't provide that.
