Re: [LTP] futex syscall tests

[Subrata Modak <subrata@linux.vnet.ibm.com>]

Hi Darren,

On Fri, 2009-07-31 at 14:29 -0700, Darren Hart wrote: 
> Mike Frysinger wrote:
> > are there any futex syscall tests already in ltp that i cant seem to locate ?  
> > if not, i can adapt the few that already exist in the libfutex code ...
> > -mike
> 
> Mike,
> 
> I recently done a lot of cleanup and a couple feature additions to the
> kernel futex code.  In doing so I was noticing the lack of a good futex
> system call test suite.  I had started a writeup of what such a test
> suite should accomplish.  I hadn't decided if I wanted to push it to LTP

I would request you to eventually push it to LTP. I think Mike might be
interested in reviewing the initial test code and then suggest his
additions/deletions. That way it would work fine, until Mike has already
written something for this.

And thanks for sharing the below design information.

Regards--
Subrata

> eventually or not.  As it sounds like you may have similar interests in
> this test, please find my very early, very incomplete, initial thoughts
> on such a testsuite.
> 
> I'd welcome your thoughts on approach, direction, etc.
> 
> -------------------------------------------------------------------------------
> 
> The following is a start at what I hope to be a design document for a new
> exhaustive futex functional/performance/stress benchmark. Before I flesh it
> out any further, I'd really appreciate some feedback on what I have so far.
> 
> Given the number of permutations each test seems to require, I think some kind
> of "test generator" is needed. We will have to describe the permutations and
> pass them to the test generator so it can create the various versions of the
> tests.
> 
> HAVOC FUTEX
> ===========
> 
> Havoc Futex is intended to thoroughly test the Linux kernel futex system call
> API. To the extent possible, each test is implemented using raw system calls
> as well as the glibc pthread library.
> 
> Futex Op Codes
> --------------
> FUTEX_WAIT
> FUTEX_WAKE
> FUTEX_FD
> FUTEX_REQUEUE
> FUTEX_CMP_REQUEUE
> FUTEX_WAKE_OP
> FUTEX_LOCK_PI
> FUTEX_UNLOCK_PI
> FUTEX_TRYLOCK_PI
> FUTEX_WAIT_BITSET
> FUTEX_WAKE_BITSET
> FUTEX_WAIT_REQUEUE_PI
> FUTEX_CMP_REQUEUE_PI
> 
> Syscalls to Test
> ----------------
> futex_wake
> futex_wake_op
> futex_requeue
> futex_wait
> futex_lock_pi
> futex_unlock_pi
> futex_wait_requeue_pi
> 
> Functional Tests
> ----------------
> requeue_pi/*
> 	Exercise the FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI op codes,
> 	under every possible combination of the following scenarios:
> 
> 	o shared and private futexes
> 	o CLOCK_MONOTONIC and CLOCK_REALTIME timeouts (and none)
> 	o Signal handling prior to and post requeue
> 	o correct and incorrect settings for val
> 	o target futex owned by waker, owned by third party, unowned
> 	o OWNERDIED reclaim of mutex
> 	o ensure priority ordered wakeup of waiters
> 
> 	Error and Misuse Cases
> 	----------------------
> 	o mixed shared and private futexes (should fail)
> 	o pi source futex
> 	o non-pi target futex
> 	o unmapped shared futex fault handling
> 	o bogus uaddrs
> 	o invalid nr_wake and nr_requeue values
> 	o mismatched wait_requeue and futex_requeue target futexes
> 	o incorrect pairing of futex_wait_requeue_pi with futex_wake
> 
> 	Syscalls Exercised
> 	------------------
> 	futex_wait_requeue_pi
> 	futex_requeue
> 	futex_lock_pi
> 	futex_unlock_pi
> 
> pi_lock/*
> 	Exercise the FUTEX_LOCK_PI and FUTEX_UNLOCK_PI op codes, under every
> 	possible combination of the following scenarious:
> 
> 	o shared and private futexes
> 	o CLOCK_MONOTONIC and CLOCK_REALTIME timeouts (and none)
> 	o Signal handling
> 	o correct and incorrect settings for val
> 	o bogus uaddrs
> 	o contended and uncontended cases
> 	o OWNERDIED reclaim of mutex
> 
> 	Error and Misuse Cases
> 	----------------------
> 	o pi_unlock of a non-pi-locked futex
> 	o pi_lock of an owned non-pi futex
> 	o unmapped shared futex fault handling
> 	o mismatched futex_lock_pi and futex_wake(_op)? calls
> 	o mismatched futex_wait and futex_unlock_pi calls
> 
> 	Syscalls Exercised
> 	------------------
> 	futex_lock_pi
> 	futex_unlock_pi
> 	futex_wait
> 	futex_wake
> 	futex_wake_op
> 
> requeue/*
> 	Exercise the FUTEX_WAIT and the FUTEX_CMP_REQUEUE op codes.  Perform
> 	basic testing for FUTEX_REQUEUE, purposefully avoiding its known
> 	flaws.
> 
> 	Error and Misuse Cases
> 	----------------------
> 
> 	Syscalls Exercised
> 	------------------
> 	futex_wait
> 	futex_requeue
> 
> wait/*
> 	Exercise the FUTEX_WAIT and FUTEX_WAKE op codes.
> 
> 	Error and Misuse Cases
> 	----------------------
> 
> 	Syscalls Exercised
> 	------------------
> 	futex_wait
> 	futex_wake
> 	futex_wake_op
> 
> 
> 
> Performance Tests
> -----------------
> 	o attempt to expose lock contention issues, such as those exposed by
> 	  calling futex_wait on an unowned futex
> 	o rapid lock and unlock of an uncontended futex
> 	o rapid lock and unlock of a heavily conteded futex
> 	o attempt to expose bottlenecks imposed by the shared hash-bucket
> 	  implementation
> 	o attempt to expose real-time scheduling overhead
> 
> Stress Tests
> ------------
> 	o thousands of threads/processes contending on a single futex
> 	o thousands of threads/processes on thousands of futexes
> 
> Other Thoughts
> --------------
> kernel-side futex fault injection
> 	There are a lot of places in futex.c that have to handle faults.  I
> 	think some kind of a fault injection system is needed.  This could be
> 	enabled via a sysctl or perhaps just configured in to a debug kernel.
> 	Running this test suite in a loop would allow us to achieve some
> 	statistical confidence in these numerous fault paths.
> 
> FUTEX_REQUEUE
> 	This op code is deprecated in favor of FUTEX_CMP_REQUEUE.  Do to the
> 	unreliable nature of the op code, only very limited testing can be
> 	performed.
> 


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