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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5
    From
    Date
    On Mon, 2004-10-18 at 16:50, Ingo Molnar wrote:
    > i have released the -U5 Real-Time Preemption patch:
    >

    starting nfsd triggers the deadlock detection, but it's not really a
    deadlock.

    The first nfsd thread acquires nlmsvc_sema. The other 7 nfsd threads
    wait on it. The first thread creates lockd and tries to get lockd_start,
    which is initialized locked and will be released when the lockd thread
    starts. The deadlock complains about a deadlock on nlmsvc_sema inside of
    down(&lockd_start). ?

    Converting lockd_start to a waitqueue solves the problem and is more
    sane, than the locked mutex.

    tglx

    --- 2.6.9-rc4-mm1-RT-U5/fs/lockd/svc.c.orig 2004-10-19
    10:02:17.000000000 +0200
    +++ 2.6.9-rc4-mm1-RT-U5/fs/lockd/svc.c 2004-10-19 09:54:22.000000000
    +0200
    @@ -46,7 +46,7 @@
    int nlmsvc_grace_period;
    unsigned long nlmsvc_timeout;

    -static DECLARE_MUTEX(lockd_start);
    +static DECLARE_WAIT_QUEUE_HEAD(lockd_start);
    static DECLARE_WAIT_QUEUE_HEAD(lockd_exit);

    /*
    @@ -109,7 +109,7 @@
    * Let our maker know we're running.
    */
    nlmsvc_pid = current->pid;
    - up(&lockd_start);
    + wake_up(&lockd_start);

    daemonize("lockd");

    @@ -230,6 +230,7 @@
    printk(KERN_WARNING
    "lockd_up: no pid, %d users??\n", nlmsvc_users);

    +
    error = -ENOMEM;
    serv = svc_create(&nlmsvc_program, LOCKD_BUFSIZE);
    if (!serv) {
    @@ -258,7 +259,19 @@
    "lockd_up: create thread failed, error=%d\n",
    error);
    goto destroy_and_out;
    }
    - down(&lockd_start);
    + /*
    + * Wait for the lockd process to start, but since we're holding
    + * the lockd semaphore, we can't wait around forever ...
    + */
    + clear_thread_flag(TIF_SIGPENDING);
    + interruptible_sleep_on_timeout(&lockd_start, HZ);
    + if (!nlmsvc_pid) {
    + printk(KERN_WARNING
    + "lockd_down: lockd failed to start\n");
    + }
    + spin_lock_irq(&current->sighand->siglock);
    + recalc_sigpending();
    + spin_unlock_irq(&current->sighand->siglock);

    /*
    * Note: svc_serv structures have an initial use count of 1,
    @@ -423,7 +436,6 @@

    static int __init init_nlm(void)
    {
    - init_MUTEX_LOCKED(&lockd_start);
    nlm_sysctl_table = register_sysctl_table(nlm_sysctl_root, 0);
    return nlm_sysctl_table ? 0 : -ENOMEM;
    }

    Installing knfsd (copyright (C) 1996 okir@monad.swb.de).
    mountdBUG: semaphore deadlock detected!
    .. task nfsd/1246 is holding c89f4560.
    00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    00000000 00000000 00000000 00000000 00000000 00000000 00000000
    00000000
    00000000 00000000 00000000 00000000 00000000 00000000 00000000
    00000000
    Call Trace:
    [<c0117fc7>] copy_process+0x5f7/0xc30
    [<c01c4e62>] __delay+0x12/0x20
    [<c01fe460>] serial8250_console_write+0x170/0x280
    [<c011930e>] __call_console_drivers+0x5e/0x60
    [<c011982a>] release_console_sem+0xda/0xe0
    [<c01196a7>] vprintk+0x107/0x160
    [<c01196a7>] vprintk+0x107/0x160
    [<c012a3ae>] __kernel_text_address+0x2e/0x40
    [<c0106bf5>] show_trace+0x35/0x90
    [<c0106bf5>] show_trace+0x35/0x90
    [<c0106cd0>] show_stack+0x80/0xa0
    [<c01c2976>] __rwsem_deadlock+0x136/0x180
    [<c01c28aa>] __rwsem_deadlock+0x6a/0x180
    [<c02c3c33>] __down_write+0x93/0x170
    [<c01c3033>] down_write+0x43/0x80
    [<c89e661d>] lockd_up+0x9d/0x120 [lockd]
    [<c89e62e0>] lockd+0x0/0x2a0 [lockd]
    [<c883d2e1>] nfsd+0x91/0x380 [nfsd]
    [<c0105e12>] ret_from_fork+0x6/0x14
    [<c883d250>] nfsd+0x0/0x380 [nfsd]
    [<c0103ffd>] kernel_thread_helper+0x5/0x18
    ...#0 task nfsd/1246 is holding c89f4560.
    BUG: semaphore deadlock: nfsd/1252 is blocked on c89f4560, deadlocking
    nfsd/1246
    c733df60 00000046 c7adad10 c03d6060 00000000 00000000 00000000 00000000
    00000000 00000000 c7a306f0 00005b6e 39133ac7 0000001a c7adae6c
    c7adad10
    c7adad10 c7584400 00000000 c02c3cad c89f4560 c6853f6c c6819f6c
    c7adad10
    Call Trace:
    [<c02c3cad>] __down_write+0x10d/0x170
    [<c01c3033>] down_write+0x43/0x80
    [<c89e6591>] lockd_up+0x11/0x120 [lockd]
    [<c883d250>] nfsd+0x0/0x380 [nfsd]
    [<c883d2e1>] nfsd+0x91/0x380 [nfsd]
    [<c0105e12>] ret_from_fork+0x6/0x14
    [<c883d250>] nfsd+0x0/0x380 [nfsd]
    [<c0103ffd>] kernel_thread_helper+0x5/0x18
    ------------[ cut here ]------------

    -
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