CVSROOT: /cvs
Module name: src
Changes by: chel...@cvs.openbsd.org 2020/04/05 20:44:31
Modified files:
sys/kern : sys_futex.c
Log message:
futex(2): FUTEX_WAIT: rwsleep_nsec(9) at least one nanosecond
mpi@ and I added a warning log to *sleep_nsec(9) last year to smoke
out division-to-zero bugs when converting kernel code from *sleep(9)
to the new interfaces. It whines if you tell it to sleep for zero
nanoseconds.
Now that rwsleep_nsec(9) is exposed to userspace via futex(2), though,
it is possible to get a legitimate zero-nanosecond timeout from the
user. This can cause a lot of logging, which apparently can cause
hiccups and hangs in Mesa.
As a quick fix we can round the timeout up to one nanosecond and
silence the warning. No logs, no delays, no hiccups or hangs.
--
Aside: it is unclear what we are supposed to do in the FUTEX_WAIT
zero-nanosecond timeout case: block for a tick or return ETIMEDOUT
immediately. The Linux futex(2) manpage does not mention the case.
It'd be nice to knew what the proper behavior is.
--
Prompted by matthieu@. Input from kettenis@ and deraadt@.
Tested by matthieu@, ajacoutot@.
In snaps since Mar 27 2020.
ok ajacoutot@, deraadt@, kettenis@.
