lkml.org 
[lkml]   [2016]   [Aug]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v10 1/2] printk: Make printk() completely async
    On (08/18/16 11:33), Petr Mladek wrote:
    [..]
    > > > 2. Force synchronous printk inside WARN()/BUG() macros.
    > >
    > > will it help? semaphore up() calls wake_up_process() regardless the context.
    > > not to mention that we still may have spin_dump() enabled.
    >
    > Good point. That changes my preferences :-)
    >
    > >
    > > > 3. Force printk_deferred() inside WARN()/BUG() macros via the per-CPU
    > > > printk_func.
    > > >
    > > > It might be elegant. But we do not want this outside the scheduler
    > > > code. Therefore we would need special variants of WARN_*_SCHED()
    > > > BUG_*_SCHED() macros.
    >
    > Also we need to make sure that everything will be done on a single CPU
    > as the printk_func is per-CPU variable.

    lib/dump_stack.c dump_stack() disables local IRQs, so we will stay
    on the same CPU.

    schematically dump_stack_deferred() looks like the one below. I don't
    dump registers, that will require one more *_deferred() function.
    and as you can see I've replaced show_stack() with save_stack_trace().
    it's not entirely universal (as of now), but worked for my needs at
    that time.

    ---

    asmlinkage __visible void dump_stack_deferred(void)
    {
    unsigned long flags;
    unsigned long stack_trace[16];
    int was_locked;
    int old, cpu;
    int i;

    struct stack_trace trace = {
    .nr_entries = 0,
    .max_entries = ARRAY_SIZE(stack_trace),
    .entries = stack_trace,
    .skip = 0,
    };

    local_irq_save(flags);
    retry:
    cpu = smp_processor_id();
    old = atomic_cmpxchg(&dump_lock, -1, cpu);
    if (old == -1) {
    was_locked = 0;
    } else if (old == cpu) {
    was_locked = 1;
    } else {
    cpu_relax();
    goto retry;
    }

    save_stack_trace(&trace);

    for (i = 0; i < trace.nr_entries; i++) {
    printk_deferred("[%p] %pS\n",
    (void *)stack_trace[i],
    (void *)stack_trace[i]);
    }

    if (!was_locked)
    atomic_set(&dump_lock, -1);

    local_irq_restore(flags);
    }

    ---

    -ss

    \
     
     \ /
      Last update: 2016-09-17 09:57    [W:4.105 / U:0.024 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site