Messages in this thread | | | Subject | Re: printk() vs tty_io | From | Peter Zijlstra <> | Date | Wed, 14 Dec 2011 11:56:46 +0100 |
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On Wed, 2011-12-14 at 10:43 +0000, Alan Cox wrote: > On Tue, 13 Dec 2011 15:52:35 -0800 > Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > On Tue, Dec 13, 2011 at 11:33 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > I've been poking at reducing the constraints on printk(), like make it > > > work under rq->lock etc.. > > > > You aren't supposed register a console that wakes things up. But the > > only console that honors that afaik is the traditional vt console. > > *Maybe* the network console, I didn't check. > > Serial console tries to be good as does netconsole.
Well, this was the 8250 serial port driver doing wakeups. Its a simple on-board serial port,
[ 29.797007] [<ffffffff8108a650>] __wake_up_common+0x4e/0x84 [ 29.797007] [<ffffffff8108d6ea>] __wake_up+0x39/0x4d [ 29.797007] [<ffffffff8135d0db>] tty_wakeup+0x5b/0x60 [ 29.797007] [<ffffffff81373fb9>] uart_write_wakeup+0x21/0x23 [ 29.797007] [<ffffffff81376899>] transmit_chars+0xd8/0x12f [ 29.797007] [<ffffffff81377f3a>] serial8250_handle_port+0x2d9/0x2fd [ 29.797007] [<ffffffff81377fcb>] serial8250_handle_irq+0x16/0x1d [ 29.797007] [<ffffffff81377ff5>] serial8250_default_handle_irq+0x23/0x27 [ 29.797007] [<ffffffff81377ade>] serial8250_interrupt+0x4d/0xc6 [ 29.797007] [<ffffffff810c9ae8>] handle_irq_event_percpu+0xab/0x1fc [ 29.797007] [<ffffffff810c9c7a>] handle_irq_event+0x41/0x61 [ 29.797007] [<ffffffff810cc4cd>] handle_edge_irq+0xd1/0xf6 [ 29.797007] [<ffffffff8103ab85>] handle_irq+0x24/0x2f [ 29.797007] [<ffffffff8150acdd>] do_IRQ+0x4d/0xb3
which places the wakeup under uport->lock, serial8250_console_write() takes uport->lock, under console_sem, connecting the locks.
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