Re: possible circular locking dependency detected [was: linux-next: Tree for Aug 22]

Boqun Feng
2017-08-24T04:39:09Z

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On Wed, Aug 23, 2017 at 02:55:17PM +0900, Sergey Senozhatsky wrote:
> On (08/23/17 13:35), Boqun Feng wrote:
> > > KERN_CONT and "\n" should not be together. "\n" flushes the cont
> > > buffer immediately.
> > >
> >
> > Hmm.. Not quite familiar with printk() stuffs, but I could see several
> > usages of printk(KERN_CONT "...\n") in kernel.
> >
> > Did a bit research myself, and I now think the inappropriate use is to
> > use a KERN_CONT printk *after* another printk ending with a "\n".
>
> ah... I didn't check __print_lock_name(): it leaves unflushed cont buffer
> upon the return. sorry, your code is correct.
>

So means printk(KERN_CON "..."); + printk(KERN_CONT "...\n") is a
correct usage, right? Thanks. Again, not familiar with printk stuff,
glad you can help me go through this ;-)

Regards,
Boqun

> -ss
>
> > > > printk("\n *** DEADLOCK ***\n\n");
> > > > + } else if (cross_lock(src->instance)) {
> > > > + printk(" Possible unsafe locking scenario by crosslock:\n\n");
> > > > + printk(" CPU0 CPU1\n");
> > > > + printk(" ---- ----\n");
> > > > + printk(" lock(");
> > > > + __print_lock_name(target);
> > > > + printk(KERN_CONT ");\n");
> > > > + printk(" lock(");
> > > > + __print_lock_name(source);
> > > > + printk(KERN_CONT ");\n");
> > > > + printk(" lock(");
> > > > + __print_lock_name(parent == source ? target : parent);
> > > > + printk(KERN_CONT ");\n");
> > > > + printk(" unlock(");
> > > > + __print_lock_name(source);
> > > > + printk(KERN_CONT ");\n");
> > > > + printk("\n *** DEADLOCK ***\n\n");
> > > > } else {
> > > > printk(" Possible unsafe locking scenario:\n\n");
> > > > printk(" CPU0 CPU1\n");
> > > > --
> > > > 2.14.1
> > > >
>
>

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