tree 5d37791218c420281e509899645d89aee7902f2b
parent 146aa1bd0511f88ddb4e92fafa2b8aad4f2f65f3
author Paul Menage <menage@google.com> 1224386884 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1224517958 -0700

cgroups: convert tasks file to use a seq_file with shared pid array

Rather than pre-generating the entire text for the "tasks" file each
time the file is opened, we instead just generate/update the array of
process ids and use a seq_file to report these to userspace.  All open
file handles on the same "tasks" file can share a pid array, which may
be updated any time that no thread is actively reading the array.  By
sharing the array, the potential for userspace to DoS the system by
opening many handles on the same "tasks" file is removed.

[Based on a patch by Lai Jiangshan, extended to use seq_file]

Signed-off-by: Paul Menage <menage@google.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>