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Description of problem:
The serial driver produces an badness message and panics in some
situations:
Kernel panic - not syncing: drivers/serial/serial_core.c:103:
spin_lock(drivers/serial/serial_core.c:c04055e0) already locked  by
drivers/serial/8250.c/1170

The program runs as normal user account, which has read and write
access to /dev/ttyS0. All the program does, is setting the low latency
mode, and then waiting, until a certain state of the handshake lines
is reached, then it sends a bytes and waits for a byte. Then it
changes the handshake lines again and the process starts again. 

The problem seems to be a race condition, as it happens not always.
On the other end of the serial line, there is a SIEMENS 5WG1 148 1AB2
EIB Buscoupler.

Photos of a panic screen are available under
http://www.auto.tuwien.ac.at/~mkoegler/linux/, serial_oops.c in the
directory is the problematic programm.

Under FC2 Kernels, the problem is the same.

The problem is also reproducesable with a normal linux pc on the other
end of the serial line.

If I run the programm, connect the serial with a null modem cable and run
echo x>/dev/ttyS0
on the other computer, I get a similar panic message.
The serial port configuration on the other computer is:
$stty -a -F/dev/ttyS0
speed 38400 baud; rows 0; columns 0; line = 0;
intr = M-G; quit = ^_; erase = ^M; kill = h; eof = <undef>; eol = 4;
eol2 = M-c; start = M-c; stop = #; susp = @; rprnt = M-~; werase = @;
lnext = <undef>; flush = #;
min = 1; time = 5;
-parenb -parodd cs8 -hupcl -cstopb cread clocal crtscts
ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl
-ixon -ixoff -iuclc -ixany -imaxbel
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0
bs0 vt0 ff0
-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase
-tostop -echoprt -echoctl -echokeport

Martin Kögler
e9925248.ac.at


Version-Release number of selected component (if applicable):
2.6.10-1.741_FC3

How reproducible:
Not every time (with the Siemens bus coupler), but the using a second
pc worked every time for the three times, I tried it.