Lock is required even if we are reading global data structure. Think about the scenario when there are two processes using the same global data structure (linked list). Let's say process1 is reading the Data Structure and process2 is modifying the Data Structure. While linked process1 is in between the linked list, process2 deletes some of the nodes from list on which process1 is currently pointing. In this case the list is corrupted and process1 will not be able to go thru the whole list. It's really imp to lock any global data structure before either reading or modifying it. Thanks & Regards, Gaurav Dhiman -----Original Message----- From: kernelnewbies-bounce@nl.linux.org [mailto:kernelnewbies-bounce@nl.linux.org] On Behalf Of manish regmi Sent: Friday, July 02, 2004 8:13 AM To: anupam.kapoor@gmail.com Cc: so_usp@yahoo.com.br; kernelnewbies@nl.linux.org Subject: Re: List of Processes >one small doubt, shouldn't we be acquiring a lock while iterating over >all the tasks ? > >anupam > > > for_each_task(p) > > { > > ... > > } > > > > You will each task's descriptor on p on each loop. The first one will be > > that of init. You will automatically break from loop when you finish > > traverse through all tasks. > > Actually a circular list. > > > > #define for_each_task(p) \ > > for (p = &init_task ; (p = p->next_task) != &init_task ; ) > > > > regards manish > > No, Lock is unnecessary here, we are not manipulating the list, just following the link. Lock is necessary if you add or remove from the list. regards manish _________________________________________________________________ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail -- 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/
