RE: 2.6.9: serial_core: uart_open

["karl malbrain" <karl@petzent.com>]

> -----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:
> > AT LAST I HAVE SOME DATA!!!
> >
> > 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.


 sh            D 00000006  3036  5341   5252                     (NOTLB)
d0408eb0 00000086 c01c14d7 00000006 d0408e94 000f4fa5 c0d38f81 000039a0
       df461240 df4613cc c035ff00 00000246 d0408ecc df461240 c0300e33
00000001
       df461240 c011c856 c035ff20 c035ff20 d0408000 00000001 c035abe0
d0408000
Call Trace:
 [<c01c14d7>] inode_has_perm+0x4c/0x54
 [<c0300e33>] __down+0x103/0x1fe
 [<c011c856>] default_wake_function+0x0/0xc
 [<c0301180>] __down_failed+0x8/0xc
 [<c021a4d0>] .text.lock.tty_io+0x87/0x10f
 [<c016d78c>] chrdev_open+0x325/0x3b9
 [<c016256f>] dentry_open+0xbd/0x180
 [<c01624ac>] filp_open+0x36/0x3c
 [<c01da502>] direct_strncpy_from_user+0x46/0x5d
 [<c0162970>] sys_open+0x31/0x7d
 [<c03036f3>] syscall_call+0x7/0xb

I believe that this is the sh process that's opening "/dev/tty"
karl m



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