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SubjectRE: 2.6.9: serial_core: uart_open
> -----Original Message-----
> From: Russell King
> Sent: Friday, July 15, 2005 12:29 AM
> To: karl malbrain
> Cc: Linux-Kernel@Vger. Kernel. Org
> Subject: Re: 2.6.9: serial_core: uart_open
> On Thu, Jul 14, 2005 at 03:35:07PM -0700, karl malbrain wrote:
> >
> > The problem is that ALL SYSTEM CALLS to open "/dev/tty" are
> blocking!! even
> > with O_NDELAY set and even from completely disjoint sessions.
> I discovered
> > this via issuing "strace sh". That's why the new xterm windows froze.
> >
> > The original process doing the open("/dev/ttyS1", O_RDWR) is
> listed in the
> > ps aux listing as status S+.
> Ok, 'S' means it's sleeping.
> Can you enable Magic SYSRQ, and ensure that you have a large kernel
> log buffer (the LOG_BUF_SHIFT configuration symbol). Ensure that
> /proc/sys/kernel/sysrq is 1, and re-run your test such that you have
> something else waiting (eg, the strace sh). Then hit Alt-SysRQ-T.
> You can then read the kernel messages with dmesg - you may need the
> -s argument to capture the entire kernel buffer.
> This will tell us where all processes are sleeping.

Here is the dump of the original process that's waiting for the
open("/dev/ttyS1", O_RDWR) to return:

test5 S C023B673 3036 5399 5224 (NOTLB)
d0fb6e88 00000086 d3462ea0 c023b673 04000000 001123f9 3949e4f7 00003b4e
d204e170 d204e2fc dfee9658 dfd4ec60 c0422448 dfee9640 c02390c0
00000000 d204e170 c011c856 00000000 00000000 c0236d4c 00000000
Call Trace:
[<c023b673>] serial8250_interrupt+0x0/0x200
[<c02390c0>] uart_block_til_ready+0x198/0x224
[<c011c856>] default_wake_function+0x0/0xc
[<c0236d4c>] uart_startup+0xb6/0x1d8
[<c011c856>] default_wake_function+0x0/0xc
[<c023980b>] uart_change_pm+0x1c/0x24
[<c023938a>] uart_open+0xd1/0x105
[<c0218226>] tty_open+0x18f/0x3b8
[<c016d78c>] chrdev_open+0x325/0x3b9
[<c016256f>] dentry_open+0xbd/0x180
[<c01624ac>] filp_open+0x36/0x3c
[<c0301e98>] __cond_resched+0x14/0x3b
[<c01da4fa>] direct_strncpy_from_user+0x3e/0x5d
[<c0162970>] sys_open+0x31/0x7d
[<c03036f3>] syscall_call+0x7/0xb

Hope this helps, karl m

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