2 files changed, 76 insertions, 31 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 665fa70e4094..20411d2876f8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -179,14 +179,11 @@ struct cgroup {
          */
         struct list_head release_list;
 
-        /* pids_mutex protects the fields below */
+        /* pids_mutex protects pids_list and cached pid arrays. */
         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;
+
+        /* Linked list of struct cgroup_pids */
+        struct list_head pids_list;
 
         /* For RCU-protected deletion */
         struct rcu_head rcu_head;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3737a682cdf5..250dac05680f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -47,6 +47,7 @@
 #include <linux/hash.h>
 #include <linux/namei.h>
 #include <linux/smp_lock.h>
+#include <linux/pid_namespace.h>
 
 #include <asm/atomic.h>
 
@@ -960,6 +961,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
         INIT_LIST_HEAD(&cgrp->children);
         INIT_LIST_HEAD(&cgrp->css_sets);
         INIT_LIST_HEAD(&cgrp->release_list);
+        INIT_LIST_HEAD(&cgrp->pids_list);
         init_rwsem(&cgrp->pids_mutex);
 }
 static void init_cgroup_root(struct cgroupfs_root *root)
@@ -2201,12 +2203,30 @@ err:
         return ret;
 }
 
+/*
+ * Cache pids for all threads in the same pid namespace that are
+ * opening the same "tasks" file.
+ */
+struct cgroup_pids {
+        /* The node in cgrp->pids_list */
+        struct list_head list;
+        /* The cgroup those pids belong to */
+        struct cgroup *cgrp;
+        /* The namepsace those pids belong to */
+        struct pid_namespace *ns;
+        /* Array of process ids in the cgroup */
+        pid_t *tasks_pids;
+        /* How many files are using the this tasks_pids array */
+        int use_count;
+        /* Length of the current tasks_pids array */
+        int length;
+};
+
 static int cmppid(const void *a, const void *b)
 {
         return *(pid_t *)a - *(pid_t *)b;
 }
 
-
 /*
  * seq_file methods for the "tasks" file. The seq_file position is the
  * next pid to display; the seq_file iterator is a pointer to the pid
@@ -2221,45 +2241,47 @@ static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
          * after a seek to the start). Use a binary-search to find the
          * next pid to display, if any
          */
-        struct cgroup *cgrp = s->private;
+        struct cgroup_pids *cp = s->private;
+        struct cgroup *cgrp = cp->cgrp;
         int index = 0, pid = *pos;
         int *iter;
 
         down_read(&cgrp->pids_mutex);
         if (pid) {
-                int end = cgrp->pids_length;
+                int end = cp->length;
 
                 while (index < end) {
                         int mid = (index + end) / 2;
-                        if (cgrp->tasks_pids[mid] == pid) {
+                        if (cp->tasks_pids[mid] == pid) {
                                 index = mid;
                                 break;
-                        } else if (cgrp->tasks_pids[mid] <= pid)
+                        } else if (cp->tasks_pids[mid] <= pid)
                                 index = mid + 1;
                         else
                                 end = mid;
                 }
         }
         /* If we're off the end of the array, we're done */
-        if (index >= cgrp->pids_length)
+        if (index >= cp->length)
                 return NULL;
         /* Update the abstract position to be the actual pid that we found */
-        iter = cgrp->tasks_pids + index;
+        iter = cp->tasks_pids + index;
         *pos = *iter;
         return iter;
 }
 
 static void cgroup_tasks_stop(struct seq_file *s, void *v)
 {
-        struct cgroup *cgrp = s->private;
+        struct cgroup_pids *cp = s->private;
+        struct cgroup *cgrp = cp->cgrp;
         up_read(&cgrp->pids_mutex);
 }
 
 static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
 {
-        struct cgroup *cgrp = s->private;
+        struct cgroup_pids *cp = s->private;
         int *p = v;
-        int *end = cgrp->tasks_pids + cgrp->pids_length;
+        int *end = cp->tasks_pids + cp->length;
 
         /*
          * Advance to the next pid in the array. If this goes off the
@@ -2286,26 +2308,33 @@ static struct seq_operations cgroup_tasks_seq_operations = {
         .show = cgroup_tasks_show,
 };
 
-static void release_cgroup_pid_array(struct cgroup *cgrp)
+static void release_cgroup_pid_array(struct cgroup_pids *cp)
 {
+        struct cgroup *cgrp = cp->cgrp;
+
         down_write(&cgrp->pids_mutex);
-        BUG_ON(!cgrp->pids_use_count);
-        if (!--cgrp->pids_use_count) {
-                kfree(cgrp->tasks_pids);
-                cgrp->tasks_pids = NULL;
-                cgrp->pids_length = 0;
+        BUG_ON(!cp->use_count);
+        if (!--cp->use_count) {
+                list_del(&cp->list);
+                put_pid_ns(cp->ns);
+                kfree(cp->tasks_pids);
+                kfree(cp);
         }
         up_write(&cgrp->pids_mutex);
 }
 
 static int cgroup_tasks_release(struct inode *inode, struct file *file)
 {
-        struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+        struct seq_file *seq;
+        struct cgroup_pids *cp;
 
         if (!(file->f_mode & FMODE_READ))
                 return 0;
 
-        release_cgroup_pid_array(cgrp);
+        seq = file->private_data;
+        cp = seq->private;
+
+        release_cgroup_pid_array(cp);
         return seq_release(inode, file);
 }
 
@@ -2324,6 +2353,8 @@ static struct file_operations cgroup_tasks_operations = {
 static int cgroup_tasks_open(struct inode *unused, struct file *file)
 {
         struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+        struct pid_namespace *ns = current->nsproxy->pid_ns;
+        struct cgroup_pids *cp;
         pid_t *pidarray;
         int npids;
         int retval;
@@ -2350,20 +2381,37 @@ static int cgroup_tasks_open(struct inode *unused, struct file *file)
          * array if necessary
          */
         down_write(&cgrp->pids_mutex);
-        kfree(cgrp->tasks_pids);
-        cgrp->tasks_pids = pidarray;
-        cgrp->pids_length = npids;
-        cgrp->pids_use_count++;
+
+        list_for_each_entry(cp, &cgrp->pids_list, list) {
+                if (ns == cp->ns)
+                        goto found;
+        }
+
+        cp = kzalloc(sizeof(*cp), GFP_KERNEL);
+        if (!cp) {
+                up_write(&cgrp->pids_mutex);
+                kfree(pidarray);
+                return -ENOMEM;
+        }
+        cp->cgrp = cgrp;
+        cp->ns = ns;
+        get_pid_ns(ns);
+        list_add(&cp->list, &cgrp->pids_list);
+found:
+        kfree(cp->tasks_pids);
+        cp->tasks_pids = pidarray;
+        cp->length = npids;
+        cp->use_count++;
         up_write(&cgrp->pids_mutex);
 
         file->f_op = &cgroup_tasks_operations;
 
         retval = seq_open(file, &cgroup_tasks_seq_operations);
         if (retval) {
-                release_cgroup_pid_array(cgrp);
+                release_cgroup_pid_array(cp);
                 return retval;
         }
-        ((struct seq_file *)file->private_data)->private = cgrp;
+        ((struct seq_file *)file->private_data)->private = cp;
         return 0;
 }