On Mon, Feb 01, 2016 at 11:31:12AM +0900, Sergey Senozhatsky wrote:
> On (01/29/16 21:43), Byungchul Park wrote:
> [..]
> > +extern int is_console_lock(raw_spinlock_t *lock);
> > +
> > static void __spin_lock_debug(raw_spinlock_t *lock)
> > {
> > u64 i;
> > @@ -113,11 +115,19 @@ static void __spin_lock_debug(raw_spinlock_t *lock)
> > return;
> > __delay(1);
> > }
> > - /* lockup suspected: */
> > - spin_dump(lock, "lockup suspected");
> > +
> > + /*
> > + * If this function is called from printk(), then we should
> > + * not call printk() more. Or it will cause an infinite
> > + * recursive cycle!
> > + */
> > + if (likely(!is_console_lock(lock))) {
> > + /* lockup suspected: */
> > + spin_dump(lock, "lockup suspected");
> > #ifdef CONFIG_SMP
> > - trigger_all_cpu_backtrace();
> > + trigger_all_cpu_backtrace();
> > #endif
> > + }
>
> /* speaking in a context of printk locks only */
>
> ... may be for a recoverable "lockup suspected" spin_dump()
> we can switch to deferred printk of the messages, which is a
> bit better than nothing. but for unrecoverable "lockup suspected"
> spin_dump() -- an actual bug (spin lock owner is not going to
> release the lock any more) -- we need something else, I think.
> the bug will neither be reported nor fixed.
Agree.
>
> -ss
>
> > /*
> > * The trylock above was causing a livelock. Give the lower level arch
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 2ce8826..568ab11 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -1981,6 +1981,11 @@ asmlinkage __visible void early_printk(const char
> > *fmt, ...)
> > }
> > #endif
> >
> > +int is_console_lock(raw_spinlock_t *lock)
> > +{
> > + return lock == &console_sem.lock;
> > +}
> > +
> > static int __add_preferred_console(char *name, int idx, char *options,
> > char *brl_options)
> > {
> > --
> > 1.9.1
> >
