Module does not run as separate thread of a process. Once we link our module to kernel using 'insmod' utility, our code becomes the kernel code and runs in privilege mode. The case you mentioned will occur when two or more that two user processes go into kernel mode that means makes a system call that invokes our modules. Let's say there are two processes, process X and process Y. Process X makes a system call which invokes Module A and Process Y makes a system call which invokes Module B. Now module B calls some function of Module A when Module A is also running on behalf of Process X. In this situation Module A is running on behalf of both Process X and Process Y. Now it will depend upon scheduler, which process is selected and made to run first. It will also depend upon if the Module A if written as reentrant or not, because if two different user threads or processes are invoking the same kernel functions (best example: device drivers) then they need to be reentrant. By reentrant we mean if the control of one thread is in a function and it sleeps in that functions that should not prevent other threads or processes to enter that function. For making the code reentrant we should keep all relevant data in local variables of a function rather than using the global variables of kernel. For more information on wait queues and reentrant code, go to following link: http://www.xml.com/ldd/chapter/book/ch05.html#t2 Hope it clears the things to some extent. Regards, GD -----Original Message----- From: kernelnewbies-bounce@nl.linux.org [mailto:kernelnewbies-bounce@nl.linux.org] On Behalf Of l x Sent: Monday, June 21, 2004 8:52 PM To: kernelnewbies@nl.linux.org Subject: Help - does module run as a single thread process? Hi, I'm working on a module and would appreciate it if some one could help me on this. Suppose there are two modules, modA and modB. What's going to happen if modB calls a function, modA_func_2(), defined in modA while modA is running another function of its own, modA_func_1()? I need modA completes modA_func_1() before responsing to modB's call to modA_func_2(). Can I assume kernel will do this for me? If I understand right, a module runs as a single thread process. Therefore, when something is running, other requests must wait. Please correct me if I'm wrong. Thanks, T. __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - 100MB free storage! http://promotions.yahoo.com/new_mail -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
