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authorZefan Li <lizefan@huawei.com>2014-09-26 00:03:25 -0400
committerTejun Heo <tj@kernel.org>2014-09-26 00:16:23 -0400
commite756c7b698604f11a979f2781d06eb7b80aba363 (patch)
treed9deebb021eb70e509f0c44b4094bc18509ea036 /kernel/cgroup.c
parent0c7bf3e8cab7900e17ce7f97104c39927d835469 (diff)
Revert "cgroup: remove redundant variable in cgroup_mount()"
This reverts commit 0c7bf3e8cab7900e17ce7f97104c39927d835469. If there are child cgroups in the cgroupfs and then we umount it, the superblock will be destroyed but the cgroup_root will be kept around. When we mount it again, cgroup_mount() will find this cgroup_root and allocate a new sb for it. So with this commit we will be trapped in a dead loop in the case described above, because kernfs_pin_sb() keeps returning NULL. Currently I don't see how we can avoid using both pinned_sb and new_sb, so just revert it. Cc: Al Viro <viro@ZenIV.linux.org.uk> Reported-by: Andrey Wagin <avagin@gmail.com> Signed-off-by: Zefan Li <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c11
1 files changed, 7 insertions, 4 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5eb20cd1709c..f873c4681316 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1694,6 +1694,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1694 struct dentry *dentry; 1694 struct dentry *dentry;
1695 int ret; 1695 int ret;
1696 int i; 1696 int i;
1697 bool new_sb;
1697 1698
1698 /* 1699 /*
1699 * The first time anyone tries to mount a cgroup, enable the list 1700 * The first time anyone tries to mount a cgroup, enable the list
@@ -1784,7 +1785,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
1784 * path is super cold. Let's just sleep a bit and retry. 1785 * path is super cold. Let's just sleep a bit and retry.
1785 */ 1786 */
1786 pinned_sb = kernfs_pin_sb(root->kf_root, NULL); 1787 pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
1787 if (IS_ERR_OR_NULL(pinned_sb) || 1788 if (IS_ERR(pinned_sb) ||
1788 !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) { 1789 !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
1789 mutex_unlock(&cgroup_mutex); 1790 mutex_unlock(&cgroup_mutex);
1790 if (!IS_ERR_OR_NULL(pinned_sb)) 1791 if (!IS_ERR_OR_NULL(pinned_sb))
@@ -1830,16 +1831,18 @@ out_free:
1830 return ERR_PTR(ret); 1831 return ERR_PTR(ret);
1831 1832
1832 dentry = kernfs_mount(fs_type, flags, root->kf_root, 1833 dentry = kernfs_mount(fs_type, flags, root->kf_root,
1833 CGROUP_SUPER_MAGIC, NULL); 1834 CGROUP_SUPER_MAGIC, &new_sb);
1834 if (IS_ERR(dentry) || pinned_sb) 1835 if (IS_ERR(dentry) || !new_sb)
1835 cgroup_put(&root->cgrp); 1836 cgroup_put(&root->cgrp);
1836 1837
1837 /* 1838 /*
1838 * If @pinned_sb, we're reusing an existing root and holding an 1839 * If @pinned_sb, we're reusing an existing root and holding an
1839 * extra ref on its sb. Mount is complete. Put the extra ref. 1840 * extra ref on its sb. Mount is complete. Put the extra ref.
1840 */ 1841 */
1841 if (pinned_sb) 1842 if (pinned_sb) {
1843 WARN_ON(new_sb);
1842 deactivate_super(pinned_sb); 1844 deactivate_super(pinned_sb);
1845 }
1843 1846
1844 return dentry; 1847 return dentry;
1845} 1848}