Commit d846687d authored by Ben Blum's avatar Ben Blum Committed by Linus Torvalds
Browse files

cgroups: use flex_array in attach_proc 



Convert cgroup_attach_proc to use flex_array.

The cgroup_attach_proc implementation requires a pre-allocated array to
store task pointers to atomically move a thread-group, but asking for a
monolithic array with kmalloc() may be unreliable for very large groups.
Using flex_array provides the same functionality with less risk of
failure.

This is a post-patch for cgroup-procs-write.patch.

Signed-off-by: default avatarBen Blum <bblum@andrew.cmu.edu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Reviewed-by: default avatarPaul Menage <menage@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 74a1166d

kernel/cgroup.c

+24 −9
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ 
#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */

#include <linux/eventfd.h>

#include <linux/poll.h>

#include <linux/flex_array.h> /* used in cgroup_attach_proc */



#include <asm/atomic.h>
@@ -1995,7 +1996,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	struct cgroupfs_root *root = cgrp->root;

	/* threadgroup list cursor and array */

	struct task_struct *tsk;

	struct task_struct **group;

	struct flex_array *group;

	/*

	 * we need to make sure we have css_sets for all the tasks we're

	 * going to move -before- we actually start moving them, so that in
@@ -2012,9 +2013,15 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	 * and if threads exit, this will just be an over-estimate.

	 */

	group_size = get_nr_threads(leader);

	group = kmalloc(group_size * sizeof(*group), GFP_KERNEL);

	/* flex_array supports very large thread-groups better than kmalloc. */

	group = flex_array_alloc(sizeof(struct task_struct *), group_size,

				 GFP_KERNEL);

	if (!group)

		return -ENOMEM;

	/* pre-allocate to guarantee space while iterating in rcu read-side. */

	retval = flex_array_prealloc(group, 0, group_size - 1, GFP_KERNEL);

	if (retval)

		goto out_free_group_list;



	/* prevent changes to the threadgroup list while we take a snapshot. */

	rcu_read_lock();
@@ -2037,7 +2044,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
		/* as per above, nr_threads may decrease, but not increase. */

		BUG_ON(i >= group_size);

		get_task_struct(tsk);

		group[i] = tsk;

		/*

		 * saying GFP_ATOMIC has no effect here because we did prealloc

		 * earlier, but it's good form to communicate our expectations.

		 */

		retval = flex_array_put_ptr(group, i, tsk, GFP_ATOMIC);

		BUG_ON(retval != 0);

		i++;

	} while_each_thread(leader, tsk);

	/* remember the number of threads in the array for later. */
@@ -2059,7 +2071,8 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
		if (ss->can_attach_task) {

			/* run on each task in the threadgroup. */

			for (i = 0; i < group_size; i++) {

				retval = ss->can_attach_task(cgrp, group[i]);

				tsk = flex_array_get_ptr(group, i);

				retval = ss->can_attach_task(cgrp, tsk);

				if (retval) {

					failed_ss = ss;

					cancel_failed_ss = true;
@@ -2075,7 +2088,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
	 */

	INIT_LIST_HEAD(&newcg_list);

	for (i = 0; i < group_size; i++) {

		tsk = group[i];

		tsk = flex_array_get_ptr(group, i);

		/* nothing to do if this task is already in the cgroup */

		oldcgrp = task_cgroup_from_root(tsk, root);

		if (cgrp == oldcgrp)
@@ -2114,7 +2127,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
			ss->pre_attach(cgrp);

	}

	for (i = 0; i < group_size; i++) {

		tsk = group[i];

		tsk = flex_array_get_ptr(group, i);

		/* leave current thread as it is if it's already there */

		oldcgrp = task_cgroup_from_root(tsk, root);

		if (cgrp == oldcgrp)
@@ -2167,10 +2180,12 @@ out_cancel_attach: 
		}

	}

	/* clean up the array of referenced threads in the group. */

	for (i = 0; i < group_size; i++)

		put_task_struct(group[i]);

	for (i = 0; i < group_size; i++) {

		tsk = flex_array_get_ptr(group, i);

		put_task_struct(tsk);

	}

out_free_group_list:

	kfree(group);

	flex_array_free(group);

	return retval;

}

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