On Mon 2019-05-06 10:16:14, Petr Mladek wrote: > On Mon 2019-05-06 09:45:53, Daniel Vetter wrote: > > console_trylock, called from within printk, can be called from pretty > > much anywhere. Including try_to_wake_up. Note that this isn't common, > > usually the box is in pretty bad shape at that point already. But it > > really doesn't help when then lockdep jumps in and spams the logs, > > potentially obscuring the real backtrace we're really interested in. > > One case I've seen (slightly simplified backtrace): > > > > Call Trace: > > <IRQ> > > console_trylock+0xe/0x60 > > vprintk_emit+0xf1/0x320 > > printk+0x4d/0x69 > > __warn_printk+0x46/0x90 > > native_smp_send_reschedule+0x2f/0x40 > > check_preempt_curr+0x81/0xa0 > > ttwu_do_wakeup+0x14/0x220 > > try_to_wake_up+0x218/0x5f0 > > try_to_wake_up() takes p->pi_lock. It could deadlock because it > can get called recursively from printk_safe_up(). > > And there are more locks taken from try_to_wake_up(), for example, > __task_rq_lock() taken from ttwu_remote(). > > IMHO, the most reliable solution would be do call the entire > up_console_sem() from printk deferred context. We could assign > few bytes for this context in the per-CPU printk_deferred > variable. Ah, I was too fast and did the same mistake. This won't help because it would still call try_to_wake_up() recursively. We need to call all printk's that can be called under locks taken in try_to_wake_up() path in printk deferred context. Unfortunately it is whack a mole approach. Best Regards, Petr _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
