cgroup: fix mount failure in a corner case (970317aa) · Commits · 戴 / test

# cat test.sh #! /bin/bash mount -t cgroup -o cpu xxx /cgroup umount /cgroup mount -t cgroup -o cpu,cpuacct xxx /cgroup umount /cgroup # ./test.sh mount: xxx already mounted or /cgroup busy mount: according to mtab, xxx is already mounted on /cgroup It's because the cgroupfs_root of the first mount was under destruction asynchronously. Fix this by delaying and then retrying mount for this case. v3: - put the refcnt immediately after getting it. (Tejun) v2: - use percpu_ref_tryget_live() rather that introducing percpu_ref_alive(). (Tejun) - adjust comment. tj: Updated the comment a bit. Cc: <stable@vger.kernel.org> # 3.15 Signed-off-by:

Li Zefan <lizefan@huawei.com> Signed-off-by:

Tejun Heo <tj@kernel.org>

kernel/cgroup.c

+23 −0

Original line number	Diff line number	Diff line
		@@ -1648,10 +1648,12 @@ static struct dentry cgroup_mount(struct file_system_type fs_type,
		int flags, const char *unused_dev_name,
		void *data)
		{
		struct cgroup_subsys *ss;
		struct cgroup_root *root;
		struct cgroup_sb_opts opts;
		struct dentry *dentry;
		int ret;
		int i;
		bool new_sb;

		/*
		@@ -1677,6 +1679,27 @@ static struct dentry cgroup_mount(struct file_system_type fs_type,
		goto out_unlock;
		}

		/*
		* Destruction of cgroup root is asynchronous, so subsystems may
		* still be dying after the previous unmount. Let's drain the
		* dying subsystems. We just need to ensure that the ones
		* unmounted previously finish dying and don't care about new ones
		* starting. Testing ref liveliness is good enough.
		*/
		for_each_subsys(ss, i) {
		if (!(opts.subsys_mask & (1 << i)) \|\|
		ss->root == &cgrp_dfl_root)
		continue;

		if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
		mutex_unlock(&cgroup_mutex);
		msleep(10);
		ret = restart_syscall();
		goto out_free;
		}
		cgroup_put(&ss->root->cgrp);
		}

		for_each_root(root) {
		bool name_match = false;

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