Re: [PATCH net-next v4 12/12] net: homa: create Makefile and Kconfig

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 6 Jan 2025 20:08:59 +0100 Andrew Lunn wrote:
> > > [   11.585197][  T133] -> #0 ((console_sem).lock){-...}-{2:2}:
> > > [ 11.585197][ T133] check_prev_add (kernel/locking/lockdep.c:3162)
> > > [ 11.585197][ T133] validate_chain (kernel/locking/lockdep.c:3281 kernel/locking/lockdep.c:3904)
> > > [ 11.585197][ T133] __lock_acquire (kernel/locking/lockdep.c:5226)
> > > [ 11.585197][ T133] lock_acquire (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5851 kernel/locking/lockdep.c:5814)
> > > [ 11.585197][ T133] _raw_spin_lock_irqsave (include/linux/spinlock_api_smp.h:111 kernel/locking/spinlock.c:162)
> > > [ 11.585197][ T133] down_trylock (kernel/locking/semaphore.c:140)
> > > [ 11.585197][ T133] __down_trylock_console_sem (kernel/printk/printk.c:326)
> > > [ 11.585197][ T133] console_trylock_spinning (kernel/printk/printk.c:2852 kernel/printk/printk.c:2009)
> > > [ 11.585197][ T133] vprintk_emit (kernel/printk/printk.c:2431 kernel/printk/printk.c:2378)
> > > [ 11.585197][ T133] vprintk (kernel/printk/printk_safe.c:86)
> > > [ 11.585197][ T133] _printk (kernel/printk/printk.c:2452)
> > > [ 11.585197][ T133] lookup_object_or_alloc+0x3d4/0x590
> > > [ 11.585197][ T133] __debug_object_init (lib/debugobjects.c:744)
> > > [ 11.585197][ T133] hrtimer_init (kernel/time/hrtimer.c:456 kernel/time/hrtimer.c:1606)
> > > [ 11.585197][ T133] homa_timer_main (net/homa/homa_plumbing.c:971)
> > > [ 11.585197][ T133] kthread (kernel/kthread.c:389)
> > > [ 11.585197][ T133] ret_from_fork (arch/x86/kernel/process.c:153)
> > > [ 11.585197][ T133] ret_from_fork_asm (arch/x86/entry/entry_64.S:254)  
> 
> Do you see something in the console log at this point?
> 
> I find it odd that hrtimer_init() results in a console message. Maybe
> the console message itself is a clue, there is something wrong with
> the timer setup. If you can avoid the console message, you might then
> avoid the later lock inversion.

Just eyeballing the code I suspect object debug is upset that
we're initializing an on-stack object. John, you should probably
switch to hrtimer_setup_on_stack() ?