From cc31edceee04a7b87f2be48f9489ebb72d264844 Mon Sep 17 00:00:00 2001 From: Paul Menage Date: Sat, 18 Oct 2008 20:28:04 -0700 Subject: 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 Reviewed-by: Lai Jiangshan Cc: Serge Hallyn Cc: Balbir Singh Cc: KAMEZAWA Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/cgroup.h | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'include/linux') diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 7166023e07d..8ab91880a0a 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -14,6 +14,7 @@ #include #include #include +#include #ifdef CONFIG_CGROUPS @@ -136,6 +137,15 @@ struct cgroup { * release_list_lock */ struct list_head release_list; + + /* pids_mutex protects the fields below */ + struct rw_semaphore pids_mutex; + /* Array of process ids in the cgroup */ + pid_t *tasks_pids; + /* How many files are using the current tasks_pids array */ + int pids_use_count; + /* Length of the current tasks_pids array */ + int pids_length; }; /* A css_set is a structure holding pointers to a set of -- cgit v1.2.3