Re: 2.6.9: serial_core: uart_open

[Russell King <rmk+lkml@arm.linux.org.uk>]

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.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core