linux-kernel - [PATCH 16/16] cgroup: allocate 2x cgrp_cset

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Message-Id: <1456351368-786-17-git-send-email-tj@kernel.org>
Date:	Wed, 24 Feb 2016 17:02:48 -0500
From:	Tejun Heo <tj@...nel.org>
To:	lizefan@...wei.com, hannes@...xchg.org
Cc:	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...com, Tejun Heo <tj@...nel.org>
Subject: [PATCH 16/16] cgroup: allocate 2x cgrp_cset_links when setting up a new root

During prep, cgroup_setup_root() allocates cgrp_cset_links matching
the number of existing css_sets to later link the new root.  This is
fine for now as the only operation which can happen inbetween is
rebind_subsystems() and rebinding of empty subsystems doesn't create
new css_sets.

However, while not yet allowed, with the recent reimplementation,
rebind_subsystems() can rebind subsystems with descendant csses and
thus can create new css_sets.  This patch makes cgroup_setup_root()
allocate 2x of the existing css_sets so that later use of live
subsystem rebinding doesn't blow up.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/cgroup.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 744e1c6..a44c123 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1914,10 +1914,11 @@ static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 	/*
 	 * We're accessing css_set_count without locking css_set_lock here,
 	 * but that's OK - it can only be increased by someone holding
-	 * cgroup_lock, and that's us. The worst that can happen is that we
-	 * have some link structures left over
+	 * cgroup_lock, and that's us.  Later rebinding may disable
+	 * controllers on the default hierarchy and thus create new csets,
+	 * which can't be more than the existing ones.  Allocate 2x.
 	 */
-	ret = allocate_cgrp_cset_links(css_set_count, &tmp_links);
+	ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
 	if (ret)
 		goto cancel_ref;

-- 
2.5.0