On Fri, 3 Apr 2020, Martin Pieuchot wrote: > Depending on the operation requested futex(2) might return the number of > woken threads or an error. That means the following... > > mpv CALL futex(0xa58935899b0,0x82<FUTEX_WAKE|FUTEX_PRIVATE_FLAG>,1,0,0) > mpv RET futex -1 errno 1 Operation not permitted > > ...is not an error but it indicates that 1 thread has been awoken. > > Diff below would have saved me quite some time looking in the wrong > direction. > > ok?
Isn't that just a complicated way to get the same effect as deleting the "case SYS_futex:" line shortly above there? The real problem is that futex(2) is actually 3 different syscalls wrapped into one. It was split into three then kdump could properly report futex_wake(2) and futex_requeue(2) as returning a count, while futex_wait(2) returns an errno. The existing 'switch' in sys_futex() would just move to userspace's futex(3), provided for linux compat. (And our syscalls would have proper prototypes and futex_wait() could take a clockid_t, and....)
