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Andrew Morton authored
From: Olaf Kirch <okir@suse.de> I have been chasing a corruption of current->group_info on PPC during NFS stress tests. The problem seems to be that nfsd is messing with its group_info quite a bit, while some monitoring processes look at /proc/<pid>/status and do a get_group_info/put_group_info without any locking. This problem can be reproduced on ppc platforms within a few seconds if you generate some NFS load and do a "cat /proc/XXX/status" of an nfsd thread in a tight loop. I therefore think changes to current->group_info, and querying it from a different process, needs to be protected using the task_lock. (akpm: task->group_info here is safe against exit() because the task holds a ref on group_info which is released in __put_task_struct, and the /proc file has a ref on the task_struct).
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