lkml.org 
[lkml]   [2012]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: lockdep trace from posix timers
    From
    Date
    On Tue, 2012-07-24 at 16:36 -0400, Dave Jones wrote:

    > ======================================================
    > [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
    > 3.5.0+ #122 Not tainted
    > ------------------------------------------------------
    > trinity-child2/5327 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
    > blocked: (tasklist_lock){.+.+..}, instance: ffffffff81c05098, at: [<ffffffff8109762b>] posix_cpu_timer_del+0x2b/0xe0
    >
    > and this task is already holding:
    > blocked: (&(&new_timer->it_lock)->rlock){-.-...}, instance: ffff880143bce170, at: [<ffffffff81093d49>] __lock_timer+0x89/0x1f0
    > which would create a new lock dependency:
    > (&(&new_timer->it_lock)->rlock){-.-...} -> (tasklist_lock){.+.+..}
    >
    > but this new dependency connects a HARDIRQ-irq-safe lock:

    > to a HARDIRQ-irq-unsafe lock:
    > (&(&p->alloc_lock)->rlock){+.+...}

    > other info that might help us debug this:
    >
    > Chain exists of:
    > &(&new_timer->it_lock)->rlock --> tasklist_lock --> &(&p->alloc_lock)->rlock
    >
    > Possible interrupt unsafe locking scenario:
    >
    > CPU0 CPU1
    > ---- ----
    > lock(&(&p->alloc_lock)->rlock);
    > local_irq_disable();
    > lock(&(&new_timer->it_lock)->rlock);
    > lock(tasklist_lock);
    > <Interrupt>
    > lock(&(&new_timer->it_lock)->rlock);
    >
    > *** DEADLOCK ***
    >
    > 1 lock on stack by trinity-child2/5327:
    > #0: blocked: (&(&new_timer->it_lock)->rlock){-.-...}, instance: ffff880143bce170, at: [<ffffffff81093d49>] __lock_timer+0x89/0x1f0


    > the dependencies between the lock to be acquired and HARDIRQ-irq-unsafe lock:

    > [<ffffffff810da83d>] lock_acquire+0xad/0x220
    > [<ffffffff816895f6>] _raw_spin_lock+0x46/0x80
    > [<ffffffff812d5f2e>] keyctl_session_to_parent+0xde/0x490
    > [<ffffffff812d634d>] sys_keyctl+0x6d/0x1a0
    > [<ffffffff8169336d>] system_call_fastpath+0x1a/0x1f

    > stack backtrace:
    > Pid: 5327, comm: trinity-child2 Not tainted 3.5.0+ #122
    > Call Trace:
    > [<ffffffff810d8194>] check_usage+0x4e4/0x500
    > [<ffffffff81023729>] ? native_sched_clock+0x19/0x80
    > [<ffffffff810d59a8>] ? trace_hardirqs_off_caller+0x28/0xd0
    > [<ffffffff81023729>] ? native_sched_clock+0x19/0x80
    > [<ffffffff810d820b>] check_irq_usage+0x5b/0xe0
    > [<ffffffff810d93da>] __lock_acquire+0xd8a/0x1ae0
    > [<ffffffff810d8956>] ? __lock_acquire+0x306/0x1ae0
    > [<ffffffff810d59a8>] ? trace_hardirqs_off_caller+0x28/0xd0
    > [<ffffffff810da2a5>] ? lock_release_non_nested+0x175/0x320
    > [<ffffffff810da83d>] lock_acquire+0xad/0x220
    > [<ffffffff8109762b>] ? posix_cpu_timer_del+0x2b/0xe0
    > [<ffffffff81689b59>] _raw_read_lock+0x49/0x80
    > [<ffffffff8109762b>] ? posix_cpu_timer_del+0x2b/0xe0
    > [<ffffffff81093d95>] ? __lock_timer+0xd5/0x1f0
    > [<ffffffff8109762b>] posix_cpu_timer_del+0x2b/0xe0
    > [<ffffffff81094786>] sys_timer_delete+0x26/0x100
    > [<ffffffff8169336d>] system_call_fastpath+0x1a/0x1f


    So we have:


    sys_keyctl()
    keyctl_session_to_parent()
    write_lock_irq(&tasklist_lock)
    task_lock(parent) parent->alloc_lock

    VS

    sys_timer_delete()
    lock_timer() timer->it_lock
    posix_cpu_timer_del()
    read_lock(&tasklist_lock)


    Creating:

    timer->it_lock -> tasklist_lock -> task->alloc_lock

    And since it_lock is IRQ-safe and alloc_lock isn't, you've got the IRQ
    inversion deadlock reported.

    The task_lock() in keyctl_session_to_parent() comes from Al who didn't
    think it necessary to write a changelog in d35abdb2.

    David, Al, anybody want to have a go at fixing this?


    \
     
     \ /
      Last update: 2012-08-16 20:41    [W:0.029 / U:0.312 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site