wireguard-openbsd/sys/kern/sys_futex.c, branch jd/queueboosts

futex(2): FUTEX_WAIT: rwsleep_nsec(9) at least one nanosecond

2020-04-06T02:44:31Z

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@.

futex(2): futex_wait(): ensure timeout is set when calling rwsleep_nsec(9)

2020-03-20T17:17:31Z

rwsleep_nsec(9) will not set a timeout if the nsecs parameter is equal to INFSLP (UINT64_MAX). We need to limit the duration to MAXTSLP (UINT64_MAX - 1) to ensure a timeout is set.

Introduce TIMESPEC_TO_NSEC() and use it to convert userland facing

2020-01-14T08:52:18Z

tsleep(9) to tsleep_nsec(9). ok bluhm@

Stop sleeping at PUSER.

2019-07-10T15:52:17Z

This allows to enforce that sleeping priorities will now always be < PUSER. ok visa@, ratchov@

Use ktrreltimespec() as the timeout is relative, pointed by matthew@.

2019-02-06T15:11:20Z

ok cheloha@

Sprinkle a pinch of timerisvalid/timespecisvalid over the rest of sys/kern

2019-01-23T21:53:42Z

futex(2): validate relative timeout before sleeping.

2019-01-18T05:06:37Z

Linux does validation. Document this new failure case as an EINVAL, like Linux. "stop waiting" deraadt

Split the system-wide list of all futexes into process-specific lists

2018-08-30T03:30:25Z

of private futexes and a shared list of shared futexes. This speeds up futex lookups. Tested by and OK krw@ OK mpi@

Implement process-shared futexes. These are now the default implementation.

2018-06-03T15:09:26Z

Introduce process-private futexs. These will bypass the uvm mapping lookup and should be slightly more efficient. ok visa@, mpi@

Make futex(2) also return ECANCELED in case SA_RESTART was set.

2018-04-24T17:19:35Z

Prodded by and ok mpi@