1 files changed, 139 insertions, 83 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1e49218457e0..046c1609606b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -868,6 +868,14 @@ static struct super_operations cgroup_ops = {
 	.remount_fs = cgroup_remount,
 };
 
+static void init_cgroup_housekeeping(struct cgroup *cgrp)
+{
+	INIT_LIST_HEAD(&cgrp->sibling);
+	INIT_LIST_HEAD(&cgrp->children);
+	INIT_LIST_HEAD(&cgrp->css_sets);
+	INIT_LIST_HEAD(&cgrp->release_list);
+	init_rwsem(&cgrp->pids_mutex);
+}
 static void init_cgroup_root(struct cgroupfs_root *root)
 {
 	struct cgroup *cgrp = &root->top_cgroup;
@@ -876,10 +884,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
 	root->number_of_cgroups = 1;
 	cgrp->root = root;
 	cgrp->top_cgroup = cgrp;
-	INIT_LIST_HEAD(&cgrp->sibling);
-	INIT_LIST_HEAD(&cgrp->children);
-	INIT_LIST_HEAD(&cgrp->css_sets);
-	INIT_LIST_HEAD(&cgrp->release_list);
+	init_cgroup_housekeeping(cgrp);
 }
 
 static int cgroup_test_super(struct super_block *sb, void *data)
@@ -1995,16 +2000,7 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
  * but we cannot guarantee that the information we produce is correct
  * unless we produce it entirely atomically.
  *
- * Upon tasks file open(), a struct ctr_struct is allocated, that
- * will have a pointer to an array (also allocated here).  The struct
- * ctr_struct * is stored in file->private_data.  Its resources will
- * be freed by release() when the file is closed.  The array is used
- * to sprintf the PIDs and then used by read().
  */
-struct ctr_struct {
-	char *buf;
-	int bufsz;
-};
 
 /*
  * Load into 'pidarray' up to 'npids' of the tasks using cgroup
@@ -2086,42 +2082,132 @@ static int cmppid(const void *a, const void *b)
 	return *(pid_t *)a - *(pid_t *)b;
 }
 
+
 /*
- * Convert array 'a' of 'npids' pid_t's to a string of newline separated
- * decimal pids in 'buf'.  Don't write more than 'sz' chars, but return
- * count 'cnt' of how many chars would be written if buf were large enough.
+ * 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
+ * in the cgroup->tasks_pids array.
  */
-static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids)
+
+static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
 {
-	int cnt = 0;
-	int i;
+	/*
+	 * Initially we receive a position value that corresponds to
+	 * one more than the last pid shown (or 0 on the first call or
+	 * after a seek to the start). Use a binary-search to find the
+	 * next pid to display, if any
+	 */
+	struct cgroup *cgrp = s->private;
+	int index = 0, pid = *pos;
+	int *iter;
 
-	for (i = 0; i < npids; i++)
-		cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
-	return cnt;
+	down_read(&cgrp->pids_mutex);
+	if (pid) {
+		int end = cgrp->pids_length;
+		int i;
+		while (index < end) {
+			int mid = (index + end) / 2;
+			if (cgrp->tasks_pids[mid] == pid) {
+				index = mid;
+				break;
+			} else if (cgrp->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)
+		return NULL;
+	/* Update the abstract position to be the actual pid that we found */
+	iter = cgrp->tasks_pids + index;
+	*pos = *iter;
+	return iter;
+}
+
+static void cgroup_tasks_stop(struct seq_file *s, void *v)
+{
+	struct cgroup *cgrp = s->private;
+	up_read(&cgrp->pids_mutex);
 }
 
+static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct cgroup *cgrp = s->private;
+	int *p = v;
+	int *end = cgrp->tasks_pids + cgrp->pids_length;
+
+	/*
+	 * Advance to the next pid in the array. If this goes off the
+	 * end, we're done
+	 */
+	p++;
+	if (p >= end) {
+		return NULL;
+	} else {
+		*pos = *p;
+		return p;
+	}
+}
+
+static int cgroup_tasks_show(struct seq_file *s, void *v)
+{
+	return seq_printf(s, "%d\n", *(int *)v);
+}
+
+static struct seq_operations cgroup_tasks_seq_operations = {
+	.start = cgroup_tasks_start,
+	.stop = cgroup_tasks_stop,
+	.next = cgroup_tasks_next,
+	.show = cgroup_tasks_show,
+};
+
+static void release_cgroup_pid_array(struct cgroup *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;
+	}
+	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);
+
+	if (!(file->f_mode & FMODE_READ))
+		return 0;
+
+	release_cgroup_pid_array(cgrp);
+	return seq_release(inode, file);
+}
+
+static struct file_operations cgroup_tasks_operations = {
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.write = cgroup_file_write,
+	.release = cgroup_tasks_release,
+};
+
 /*
- * Handle an open on 'tasks' file.  Prepare a buffer listing the
+ * Handle an open on 'tasks' file.  Prepare an array containing the
  * process id's of tasks currently attached to the cgroup being opened.
- *
- * Does not require any specific cgroup mutexes, and does not take any.
  */
+
 static int cgroup_tasks_open(struct inode *unused, struct file *file)
 {
 	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
-	struct ctr_struct *ctr;
 	pid_t *pidarray;
 	int npids;
-	char c;
+	int retval;
 
+	/* Nothing to do for write-only files */
 	if (!(file->f_mode & FMODE_READ))
 		return 0;
 
-	ctr = kmalloc(sizeof(*ctr), GFP_KERNEL);
-	if (!ctr)
-		goto err0;
-
 	/*
 	 * If cgroup gets more users after we read count, we won't have
 	 * enough space - tough.  This race is indistinguishable to the
@@ -2129,57 +2215,31 @@ static int cgroup_tasks_open(struct inode *unused, struct file *file)
 	 * show up until sometime later on.
 	 */
 	npids = cgroup_task_count(cgrp);
-	if (npids) {
-		pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
-		if (!pidarray)
-			goto err1;
-
-		npids = pid_array_load(pidarray, npids, cgrp);
-		sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
-
-		/* Call pid_array_to_buf() twice, first just to get bufsz */
-		ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1;
-		ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL);
-		if (!ctr->buf)
-			goto err2;
-		ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids);
-
-		kfree(pidarray);
-	} else {
-		ctr->buf = NULL;
-		ctr->bufsz = 0;
-	}
-	file->private_data = ctr;
-	return 0;
-
-err2:
-	kfree(pidarray);
-err1:
-	kfree(ctr);
-err0:
-	return -ENOMEM;
-}
-
-static ssize_t cgroup_tasks_read(struct cgroup *cgrp,
-				    struct cftype *cft,
-				    struct file *file, char __user *buf,
-				    size_t nbytes, loff_t *ppos)
-{
-	struct ctr_struct *ctr = file->private_data;
+	pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
+	if (!pidarray)
+		return -ENOMEM;
+	npids = pid_array_load(pidarray, npids, cgrp);
+	sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
 
-	return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz);
-}
+	/*
+	 * Store the array in the cgroup, freeing the old
+	 * array if necessary
+	 */
+	down_write(&cgrp->pids_mutex);
+	kfree(cgrp->tasks_pids);
+	cgrp->tasks_pids = pidarray;
+	cgrp->pids_length = npids;
+	cgrp->pids_use_count++;
+	up_write(&cgrp->pids_mutex);
 
-static int cgroup_tasks_release(struct inode *unused_inode,
-					struct file *file)
-{
-	struct ctr_struct *ctr;
+	file->f_op = &cgroup_tasks_operations;
 
-	if (file->f_mode & FMODE_READ) {
-		ctr = file->private_data;
-		kfree(ctr->buf);
-		kfree(ctr);
+	retval = seq_open(file, &cgroup_tasks_seq_operations);
+	if (retval) {
+		release_cgroup_pid_array(cgrp);
+		return retval;
 	}
+	((struct seq_file *)file->private_data)->private = cgrp;
 	return 0;
 }
 
@@ -2208,7 +2268,6 @@ static struct cftype files[] = {
 	{
 		.name = "tasks",
 		.open = cgroup_tasks_open,
-		.read = cgroup_tasks_read,
 		.write_u64 = cgroup_tasks_write,
 		.release = cgroup_tasks_release,
 		.private = FILE_TASKLIST,
@@ -2298,10 +2357,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
 	mutex_lock(&cgroup_mutex);
 
-	INIT_LIST_HEAD(&cgrp->sibling);
-	INIT_LIST_HEAD(&cgrp->children);
-	INIT_LIST_HEAD(&cgrp->css_sets);
-	INIT_LIST_HEAD(&cgrp->release_list);
+	init_cgroup_housekeeping(cgrp);
 
 	cgrp->parent = parent;
 	cgrp->root = parent->root;