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Problem Report 1278 Details

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Report 1278 Actions

    Problem Report Number 1278
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Test Suite Deficiency (TSD)
    Problem Resolution ID TSD.X.0560
    Raised 1970-01-01 08:00
    Updated 2003-03-13 08:00
    Published 1998-09-22 08:00
    Product Standard Sockets (UNIX 95)
    Certification Program The Open Brand certification program
    Test Suite VSU version 4.1.1
    Test Identification CAPIsockets/fconnect1.c 4
    Problem Summary TSD4U.00258 This test may fail because of a race condition.
    Problem Text
    PROBLEM:

    This test is testing whether connect returns "ETIMEDOUT" when
    blocked I/O is terminated because of timeout expiration. In our case,
    it sometimes finishes in an unresolved state because of a connect
    failure in AF_UNIX code around line 1510 due to the fact that
    the UNIX Domain socket is removed before the parent process can
    connect to it. However, the problem isn't caused by the misbehavior
    of connect; rather, it's caused by the dependencies created
    between the AF_INET child and AF_UNIX child through semaphores.
    Basically, at the end of the AF_INET test case, the parent process
    is supposed to change semop to 1 for semnum#2 (the one AF_INET
    child is sleeping for), and thus wake up this child. However, right
    after doing so, the parent will continue and create the AF_UNIX
    child. After the AF_UNIX child gets the CPU, it will also try
    to wait for the parent on the semnum#2. This is where the race
    between 2 child processes exist. The test result depends on who
    sees the parent's change to semnum#2 first. If AF_INET child sees
    it first, the test will pass; on the other hand, if AF_UNIX child
    sees it first and is able to execute the socket close before the
    parent process can execute the connect call, the test may fail.
    Because of this sensitivity to process scheduling, the test does not
    fail consistently. In fact, it usually passes. We have seen the
    problem most often on uniprocessor systems, probably
    because process scheduling is more serialized.

    *****************************************************************************
    EXAMPLES:

    The following are behaviors of the parent, child#1(forked from AF_INET
    case) and child#2(forked from AF_UNIX case) put into chronological
    order that we observe for both PASS and UNRESOLVED cases

    Note:
    post---means "avs_post_event" is being called, and sem_op is 1.
    wait---means "avs_wait_event" is being called, and sem_op is -1.


    For the PASS case, this is what's happening,

    Parent: Child #1 (AF_INET): Child #2 (AF_UNIX)
    ------- ------------------- ------------------
    1. fork Child #1 0. start
    1. post Event #4
    2. wait for Event #4
    3. post Event #2
    4. fork Child #2 0. start
    2. wait for Event #2 1. create socket (bind)
    3. exit 2. post Event #4
    5. wait for Event #4
    6. access socket (connect)
    7. post Event #2 3. wait for Event #2
    8. exit 4. remove socket (close)
    5. exit


    For the UNRESOLVED case,

    Parent: Child #1 (AF_INET): Child #2 (AF_UNIX)
    ------- ------------------- ------------------
    1. fork Child #1 0. start
    1. post Event #4
    2. wait for Event #4
    3. post Event #2
    4. fork Child #2 0. start
    1. create socket (bind)
    2. post Event #4
    3. wait for Event #2
    4. remove socket (close)
    5. exit
    5. wait for Event #4
    6. access socket (connect; fails)
    7. ....
    8. error exit 2. wait for Event #2 (times out)
    3. error exit

    *****************************************************************************
    ANALYSIS:

    As we can see from the unresolved case, after the parent changes
    the semop to 1 for semnum 2, child 2, instead of child 1, can get
    the control of CPU until it reaches step 3. At this point, it can
    wrongfully assume that the parent has already posted the event,
    and thus not wait for the semaphore. Consequently, it will continue
    its operation and close and remove the socket while the parent is
    still assuming that the child is still active, and it can connect
    to the Unix Domain socket created by the child.

    *****************************************************************************
    SUGGESTED WORK AROUND:

    Use a different set of semaphores, either semid or semnum
    (in struct sembuf), for each parent/child pair---for example, for
    each AF_INET and AF_UNIX path. This change will keep the intention
    of the test case without causing the unintended dependencies.

    Test Output
    520|1 4 19712 1 1|SPEC1170TESTSUITE CASE 4
    520|1 4 19712 1 2|If the implementation supports a communications domain
    520|1 4 19712 1 3|and a connection-oriented socket type:
    520|1 4 19712 1 4|A call to int connect(int socket, const struct
    520|1 4 19712 1 5|sockaddr *address, size_t address_len) when blocking
    520|1 4 19712 1 6|is terminated due to expiration of the timeout shall
    520|1 4 19712 1 7|abort the connection attempt, set errno to ETIMEDOUT,
    520|1 4 19712 1 8|and return -1.
    520|1 4 19734 1 1|PREP: Get VSU_CONNECT_TIMEOUT configuration variable
    520|1 4 19734 1 2|TEST: AF_INET SOCK_STREAM
    520|1 4 19734 1 3|PREP: Create test sockaddr_in: address = 15.0.69.35,
    port = 4357
    520|1 4 19735 1 1|PREP: Child: create socket
    520|1 4 19735 1 2|PREP: Child: bind to socket
    520|1 4 19735 1 3|PREP: Child: listen on socket with backlog of 2
    520|1 4 19735 1 4|PREP: Child: tell parent ready
    520|1 4 19735 1 5|PREP: Child: wait for parent to complete
    520|1 4 19734 2 1|PREP: Create three sockets
    520|1 4 19734 2 2|PREP: Wait for child to be ready
    520|1 4 19734 2 3|PREP: Connect twice to fill queue
    520|1 4 19734 2 4|PREP: Set long alarm
    520|1 4 19734 2 5|TEST: connect blocks until timeout elapses
    520|1 4 19734 2 6|TEST: Return value
    520|1 4 19734 2 7|TEST: errno value
    520|1 4 19734 2 8|TEST: Blocked for correct interval
    520|1 4 19734 2 9|CLEANUP: Close sockets, end child
    520|1 4 19734 2 10|INFO: Notify waiting child
    520|1 4 19734 2 11|TEST: AF_UNIX SOCK_STREAM
    520|1 4 19734 2 12|PREP: Create test sockaddr_un: path =

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    We agree this is a test suite deficiency in the test
    suite version(s) listed.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Test Suite Deficiency (TSD)
    Review Conclusion
    This is an agreed Test Suite Deficiency.

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