Made a mistake again.. :(
==============
From: Li Zefan <lize...@huawei.com>
Subject: [PATCH 1/3] cgroup: fix mount failure in a corner case
# 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.
v2:
- use percpu_ref_tryget_live() rather that introducing
percpu_ref_alive(). (Tejun)
- adjust comment.
Signed-off-by: Li Zefan <lize...@huawei.com>
---
kernel/cgroup.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1c65f24..b94449f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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, j = -1;
bool new_sb;
/*
@@ -1677,6 +1679,25 @@ static struct dentry *cgroup_mount(struct
file_system_type *fs_type,
goto out_unlock;
}
+ /*
+ * Destruction of cgroup root is asynchronous, so we may fail to
+ * mount a cgroupfs if it immediately follows a umount. Let's wait
+ * a little bit and retry.
+ */
+ 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;
+ }
+ j = i;
+ }
+
for_each_root(root) {
bool name_match = false;
@@ -1763,6 +1784,14 @@ out_free:
kfree(opts.release_agent);
kfree(opts.name);
+ for_each_subsys(ss, i) {
+ if (i > j)
+ break;
+ if (!(opts.subsys_mask & (1 << i)))
+ continue;
+ cgroup_put(&ss->root->cgrp);
+ }
+
if (ret)
return ERR_PTR(ret);
--
1.8.0.2
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