Hi,

I have a module which reads all the tasks in the system via task_struct structure and logs that information in /proc/process_info ( a dynamically created file in /proc by the module). It works fine if access the fields of
task struct like sleep_avg,prio, static_prio etc. But if I try to access the task->mm-> ANY FIELD , like mm->task_size mm->mm_count etc and try to view the /proc/process_info with vim , the vim comes out with segmentation fault.

I have no clue What is the issue here.. Thanks for any help...

I presume that what you are doing cannot be handled by /proc/taskid/(whatever...)?

Or by any of the existing counters and metrics already available in the kernel?

Within the kernel, accessing any one of the task-structures is comparatively easy (so long as you properly lock it), and accessing a list of task-IDs is also comparatively easy. But in the general case, attempting to access every task in-detail would be a very expensive and failure-prone thing to do. Especially in a multiprocessor system: it would basically force the whole world to stop and wait for you.

You see, "the lock that owns the task-list" does not cover every task structure in that list: each one of these is individually locked. The task-list locks simply regulate insertion and deletion, i.e. the integrity of the list itself.

If you can by any means accomplish your objective, "close-enough," by means of the existing information published to user-space in /proc/taskid, you should definitely do so.