linux-kernel - Re: open() on /dev/tty takes 30 seconds on 2.6.36

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Date:	Wed, 03 Nov 2010 02:15:04 +0200
From:	Eli Billauer <eli@...lauer.co.il>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Greg KH <greg@...ah.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: open() on /dev/tty takes 30 seconds on 2.6.36

Arnd Bergmann wrote:

> Ok, that's certainly modem-manager in the tty_release function, calling
> uart_close, which has this code:
>
>         if (port->closing_wait != ASYNC_CLOSING_WAIT_NONE) {
>                 /*
>                  * hack: open-coded tty_wait_until_sent to avoid
>                  * recursive tty_lock
>                  */
>                 long timeout = msecs_to_jiffies(port->closing_wait);
>                 if (wait_event_interruptible_timeout(tty->write_wait,
>                                 !tty_chars_in_buffer(tty), timeout) >= 0)
>                         __uart_wait_until_sent(uport, timeout);
>         }
>
> port->closing_wait gets initialized to 30 seconds, which fits your
> symptom.
>   
I lost you here. Maybe my version is outdated? The most similar thing I 
have is this in tty_port.c, in tty_port_close_start():

    if (test_bit(ASYNCB_INITIALIZED, &port->flags) &&
            port->closing_wait != ASYNC_CLOSING_WAIT_NONE)
        tty_wait_until_sent(tty, port->closing_wait);

I put a printk on invocations of tty_wait_until_sent(), which was called 
like crazy during bootup on behalf of tty1, and then never again after 
boot was completed. I should point out, that during this session, all I 
did was to wait a few minutes and then reboot the computer from the GUI 
login console. So I never logged in. Anyhow, the ttySx ports were opened 
and closed, the same 30 seconds delays, but no call to 
tty_wait_until_sent() until kernel logging was stopped.

> What does "lspci -vvx" show about the
> port? 
It turns out, that the device, to which ttyS1-ttyS3 are attached is a 
soft modem, which doesn't even have drivers for a 64 bits system. There 
is no /dev/ttyS4, which is consistent with the "Couldn't register serial 
port 0000:05:04.0: -28" message. Anyhow, I can't say I understand why 
any serial port was allocated to this modem. But it's not like I 
understand how it should work.

05:04.0 Modem: ALi Corporation SmartLink SmartPCI563 56K Modem (prog-if 
00 [Generic])
    Subsystem: Device 2020:545a
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR- FastB2B- DisINTx-
    Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 32
    Interrupt: pin A routed to IRQ 16
    Region 0: Memory at fbbff000 (32-bit, non-prefetchable) [size=4K]
    Region 1: I/O ports at be00 [size=256]
    Capabilities: [40] Power Management version 2
        Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA 
PME(D0-,D1-,D2-,D3hot+,D3cold+)
        Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
    Kernel driver in use: serial
00: b9 10 5a 54 07 00 90 02 00 00 03 07 00 20 00 00
10: 00 f0 bf fb 01 be 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 20 20 5a 54
30: 00 00 00 00 40 00 00 00 00 00 00 00 0b 01 00 00

   Eli

-- 
Web: http://www.billauer.co.il

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