On Wed 2019-10-09 10:46:14, Qian Cai wrote: > On Wed, 2019-10-09 at 16:24 +0200, Petr Mladek wrote: > > On Wed 2019-10-09 09:43:13, Qian Cai wrote: > > > On Wed, 2019-10-09 at 15:27 +0200, Michal Hocko wrote: > > > > On Wed 09-10-19 09:06:42, Qian Cai wrote: > > > > [...] > > > > > https://lore.kernel.org/linux-mm/1570460350.5576.290.camel@xxxxxx/ > > > > > > > > > > [ 297.425964] -> #1 (&port_lock_key){-.-.}: > > > > > [ 297.425967] __lock_acquire+0x5b3/0xb40 > > > > > [ 297.425967] lock_acquire+0x126/0x280 > > > > > [ 297.425968] _raw_spin_lock_irqsave+0x3a/0x50 > > > > > [ 297.425969] serial8250_console_write+0x3e4/0x450 > > > > > [ 297.425970] univ8250_console_write+0x4b/0x60 > > > > > [ 297.425970] console_unlock+0x501/0x750 > > > > > [ 297.425971] vprintk_emit+0x10d/0x340 > > > > > [ 297.425972] vprintk_default+0x1f/0x30 > > > > > [ 297.425972] vprintk_func+0x44/0xd4 > > > > > [ 297.425973] printk+0x9f/0xc5 > > > > > [ 297.425974] register_console+0x39c/0x520 > > > > > [ 297.425975] univ8250_console_init+0x23/0x2d > > > > > [ 297.425975] console_init+0x338/0x4cd > > > > > [ 297.425976] start_kernel+0x534/0x724 > > > > > [ 297.425977] x86_64_start_reservations+0x24/0x26 > > > > > [ 297.425977] x86_64_start_kernel+0xf4/0xfb > > > > > [ 297.425978] secondary_startup_64+0xb6/0xc0 > > > > > > > > > > where the report again show the early boot call trace for the locking > > > > > dependency, > > > > > > > > > > console_owner --> port_lock_key > > > > > > > > > > but that dependency clearly not only happen in the early boot. > > > > > > > > Can you provide an example of the runtime dependency without any early > > > > boot artifacts? Because this discussion really doens't make much sense > > > > without a clear example of a _real_ lockdep report that is not a false > > > > possitive. All of them so far have been concluded to be false possitive > > > > AFAIU. > > > > > > An obvious one is in the above link. Just replace the trace in #1 above with > > > printk() from anywhere, i.e., just ignore the early boot calls there as they are > > > not important. > > > > > > printk() > > > console_unlock() > > > console_lock_spinning_enable() --> console_owner_lock > > > call_console_drivers() > > > serial8250_console_write() --> port->lock > > > > Please, find the location where this really happens and then suggests > > how the real deadlock could get fixed. So far, we have seen only > > false positives and theoretical scenarios. > > Now the bar is higher again. You are now asking me to actually trigger this > potential deadlock live. I am probably better off buying some lottery tickets > then if I could be that lucky. No, we just do not want to comlicate the code too much just to hide false positives from lockdep. I do not ask you to reproduce the deadlock. I ask you to find a code path where the deadlock might really happen. It seems that you actually found one in the tty code in the other mail. Best Regards, Petr
