lkml.org 
[lkml]   [2008]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled
    * Steven Rostedt (rostedt@goodmis.org) wrote:
    >
    > On Wed, 23 Jan 2008, Daniel Walker wrote:
    >
    > >
    > > On Wed, 2008-01-23 at 11:02 -0500, Steven Rostedt wrote:
    > >
    > > > + if (!irqs_disabled() && wake_klogd)
    > > > wake_up_klogd();
    > >
    > > This causes a regression .. When printk is called during an OOPS in
    > > kernels without this change then the OOPS will get logged, since the
    > > logging process (klogd) is woken to handle the messages.. If you apply
    > > this change klogd doesn't wakeup, and hence doesn't log the oops.. So if
    > > you remove the wakeup here you have to add it someplace else to maintain
    > > the logging ..
    > >
    > > (I'm not theorizing here, I have defects logged against this specific
    > > piece of code..)
    >
    > It wont get woken up anyway. Did you look at wake_up_klogd?
    >
    > void wake_up_klogd(void)
    > {
    > if (!oops_in_progress && waitqueue_active(&log_wait))
    > wake_up_interruptible(&log_wait);
    > }
    >
    >
    > So if oops_in_progress is set, then it still wont get woken. Perhaps it
    > got woken some other way? Or is oops_in_progress not set in these oops?
    >
    > One other solution is to make the runqueue locks visible externally. Like:
    >
    > in sched.c:
    >
    > int runqueue_is_locked(void)
    > {
    > int cpu = get_cpu();
    > struct rq *rq = cpu_rq(cpu);
    > int ret;
    >
    > ret = spin_is_locked(&rq->lock);
    > put_cpu();
    > return ret;
    > }
    >
    > And in printk we could do:
    >
    > if (wake_klogd && !runqueue_is_locked())
    > wake_up_klogd();
    >
    > This probably is the cleanest solution since it simply prevents the
    > deadlock from occurring.
    >


    FYI :

    kernel/panic.c

    NORET_TYPE void panic(const char * fmt, ...)
    {
    ....
    bust_spinlocks(1);
    ...
    bust_spinlocks(0);
    ...

    In bust_spinlocks :


    void __attribute__((weak)) bust_spinlocks(int yes)
    {
    if (yes) {
    ++oops_in_progress;
    } else {
    #ifdef CONFIG_VT
    unblank_screen();
    #endif
    if (--oops_in_progress == 0)
    wake_up_klogd();
    }
    }

    Where the final wake_up happens while oops_in_progress is 0, but
    interrupts are still disabled.

    So about my previous email, proposing testing oops_in_progress, it just
    won't work.

    Mathieu

    > -- Steve
    >

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


    \
     
     \ /
      Last update: 2008-01-23 18:47    [W:0.041 / U:34.460 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site