Kernel module function call

The stack trace is saying that the previous python command got wedged in spinlock trying to free the mutex on exit (something has gone horribly wrong). POSIX states you can't free the mutex from a different thread than the one that entered it. The next step is to figure out what resource is causing the mutex to be held on exit. From:

linux-source-2.6.38/kernel/mutex.c:
     69  * The mutex must later on be released by the same task that
     70  * acquired it. Recursive locking is not allowed. The task
     71  * may not exit without first unlocking the mutex. Also, kernel
     72  * memory where the mutex resides mutex must not be freed with
     73  * the mutex still locked. The mutex must first be initialized
     74  * (or statically defined) before it can be locked. memset()-ing
     75  * the mutex to 0 is not allowed.

You could start by stracing the python or by enabling dtrace on the driver.

In the case of Linux, a task (kernel internal idea of a thread; threads can share resources, like memory and open files; some run only inside the kernel) can run in userland, or (it's thread of execution) can transfer into the kernel (and back) to execute a system call. A user thread can be highjacked temporarily to execute an interrupt (but that isn't really that thread running).

That a process is a "system process" or a regular user process is completely irrelevant in Unix, they are handled just the same. In Linux case, some tasks run in-kernel to handle miscellaneous jobs. They are kernel jobs, not "system processes" however.

One big caveat: Text books on complex software products (compilers and operating systems are particularly egregious examples) tend to explain simplistic algorithms (often ones that haven't been used in earnest for half a century), because real world machines and user requirements are much too complex to be handled in some way that can be described in a structured, simple way. Much of a compiler is ad-hoc tweaks (particularly in the area of code optimization, the transformations are mostly the subset of possibilities that show up in practical use). In the case of Linux, most of the code is device drivers (mentioned in passing as device-dependent in operating system texts), and of this code a hefty slice is handling misbehaving devices, which do not comply to their own specifications, or which behave differently between versions of "the same device". Often what is explained in minute detail is just the segment of the job that can be reduced to some nice theory, leaving the messy, irregular part (almost) completely out. For instance, Cris Fraser and David Hanson in their book describing the LCC compiler state that typical compiler texts contain mostly explanations on lexical analysis and parsing, and very little on code generation. Those tasks are some 5% of the code of their (engineered to be simple!) compiler, and had negligible error rate. The complex part of the compiler is just not covered in standard texts.