CS3 Operating Systems 2013-14, Practical Exercise.

PHASE 3
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The assessed submission for this practical comprises three
installments. This is the second installment.

Part 2
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In this part, you need to prepare three files for submission.
The first is a text file containing your description and analysis
of a problem; the second is a corrected version of a program;
the third is dmesg output as in Part 1.
The text file should be called part2-analysis; the program should
be called fixedworker.c; the output should be called  part2-output .


Consider the  worker  module from Part 1.

Recall that when the module is rmmod'ed, it sets a flag to ask the
kernel thread to stop, and then waits to be told by the thread that it
is done. On a uniprocessing, unmodified, Linux system, this technique is
safe, because kernel routines cannot be pre-empted. On an SMP system,
however, the kernel thread might be running at the same time as the
rmmod command.

In the directory   /group/teaching/cs3/os/Modules
there is a slightly modified worker, called  stuckworker.c ,
which contains a delay to simulate the effect of possible
multiprocessing.

Copy this file (and the Makefile - or update your own Makefile appropriately).

Compile and install this module, and then do exactly what you did for
worker, namely, insmod, wait thirty seconds, and rmmod .

In the file  part2-analysis:
 Describe what happens. 
  [ You should not exceed 10 lines ]
 Analyse the cause of the problem. 
  [ You should not exceed 10 lines ]
 Propose and explain a solution for an SMP-safe version of worker .
  [ You should not need more than 20 lines ]

Implement your solution in  fixedworker.c.

Run your  fixedworker  in the usual way, and capture the dmesg output
in your  part2-output  file.

[ Hints: there are several ways to do this.
  You may find the   wait_event   macro (in <linux/wait.h>) of
  interest.
  You are free to use Google to assist you in solving this problem,
  but you should not consult humans.
  If you use a solution based on something on the net, you should
  acknowledge your source. Of course, you must understand and explain
  your solution.
]


When you have finished this part, and no later than the final
practical deadline, submit your files with the command

submit os 1 part2-analysis fixedworker.c part2-output

DO NOT submit any other files, or use any other name for the
files. Such files will not be marked.


This part contributes 30% of the practical.
If you have done the suggested reading and followed lectures, it
should take at most a couple of hours, and possibly much less.