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
