[Devel] [PATCH RHEL7 COMMIT] cgroup: add export_operations to cgroup super block
Vasily Averin
vvs at virtuozzo.com
Wed Aug 5 21:44:48 MSK 2020
The commit is pushed to "branch-rh7-3.10.0-1127.18.2.vz7.163.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.18.2.el7
------>
commit 9981d60d0996917b21df1ff87de8fb551a128807
Author: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Date: Wed Aug 5 21:44:46 2020 +0300
cgroup: add export_operations to cgroup super block
criu uses fhandle from fdinfo to dump inotify objects. cgroup super block has
no export operations, but .encode_fh and .fh_to_dentry are needed for
inotify_fdinfo function and open_by_handle_at syscall in order to correctly
open files located on cgroupfs by fhandle.
Add hash table as a storage for inodes with exported fhandle.
v3: use inode->i_gen to protect from i_ino reusage. increase fhandle size to
2 * u32.
Add an option to take reference of inode in cgroup_find_inode, so no one can
delete recently found inode.
v4: introduced hashtable helper functions to avoid races.
changed i_gen generation from get_seconds to prandom_u32.
https://jira.sw.ru/browse/PSBM-105889
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
kernel/cgroup.c | 168 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 167 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9fdba79..956a9ac 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -62,6 +62,8 @@
#include <linux/kthread.h>
#include <linux/ve.h>
#include <linux/stacktrace.h>
+#include <linux/exportfs.h>
+#include <linux/random.h>
#include <linux/atomic.h>
@@ -765,6 +767,7 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
if (inode) {
inode->i_ino = get_next_ino();
+ inode->i_generation = prandom_u32();
inode->i_mode = mode;
inode->i_uid = current_fsuid();
inode->i_gid = current_fsgid();
@@ -1390,9 +1393,171 @@ out:
}
#endif
+/*
+ * hashtable for inodes that have exported fhandles.
+ * When we export fhandle, we add it's inode into
+ * hashtable so we can find it fast
+ */
+
+#define CGROUP_INODE_HASH_BITS 10
+static DEFINE_HASHTABLE(cgroup_inode_table, CGROUP_INODE_HASH_BITS);
+static DEFINE_SPINLOCK(cgroup_inode_table_lock);
+
+struct cg_inode_hitem {
+ struct inode *inode;
+ struct hlist_node hlist;
+};
+
+static inline unsigned long cgroup_inode_get_hash(unsigned int i_ino)
+{
+ return hash_32(i_ino, CGROUP_INODE_HASH_BITS);
+}
+
+static struct cg_inode_hitem *cgroup_find_item_no_lock(unsigned long fh[2])
+{
+ struct cg_inode_hitem *i;
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(fh[1]);
+ struct cg_inode_hitem *found = NULL;
+
+ hlist_for_each_entry(i, head, hlist) {
+ if (i->inode->i_generation == fh[0] &&
+ i->inode->i_ino == fh[1]) {
+ found = i;
+ break;
+ }
+ }
+
+ return found;
+}
+
+static struct inode *cgroup_find_inode(unsigned long fh[2], char take_ref)
+{
+ struct cg_inode_hitem *item;
+ struct inode *ret = NULL;
+
+ spin_lock(&cgroup_inode_table_lock);
+ item = cgroup_find_item_no_lock(fh);
+
+ /*
+ * If we need to increase refcount, we should be aware of possible
+ * deadlock. Another thread may have started deleting this inode:
+ * iput->iput_final->cgroup_delete_inode->cgroup_hash_del
+ * If we just call igrab, it will try to take i_lock and this will
+ * result in deadlock, because deleting thread has already taken it
+ * and waits on cgroup_inode_table_lock to find inode in hashtable.
+ *
+ * If i_count is zero, someone is deleting it -> skip.
+ */
+ if (take_ref && item)
+ if (!atomic_inc_not_zero(&item->inode->i_count))
+ item = NULL;
+
+ spin_unlock(&cgroup_inode_table_lock);
+
+ if (item)
+ ret = item->inode;
+
+ return ret;
+}
+
+static int cgroup_hash_add(struct inode *inode)
+{
+ unsigned long fh[2] = {inode->i_generation, inode->i_ino};
+
+ if (!cgroup_find_inode(fh, 0)) {
+ struct cg_inode_hitem *item;
+ struct cg_inode_hitem *existing_item = 0;
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(inode->i_ino);
+
+ item = kmalloc(sizeof(struct cg_inode_hitem), GFP_KERNEL);
+ if (!item)
+ return -ENOMEM;
+ item->inode = inode;
+
+ spin_lock(&cgroup_inode_table_lock);
+ existing_item = cgroup_find_item_no_lock(fh);
+ if (!existing_item)
+ hlist_add_head(&item->hlist, head);
+ spin_unlock(&cgroup_inode_table_lock);
+
+ if (existing_item)
+ kfree(item);
+ }
+
+ return 0;
+}
+
+static void cgroup_hash_del(struct inode *inode)
+{
+ struct cg_inode_hitem *item;
+ unsigned long fh[2] = {inode->i_generation, inode->i_ino};
+
+ spin_lock(&cgroup_inode_table_lock);
+ item = cgroup_find_item_no_lock(fh);
+ if (item)
+ hlist_del(&item->hlist);
+ spin_unlock(&cgroup_inode_table_lock);
+
+ kfree(item);
+ return;
+}
+
+static struct dentry *cgroup_fh_to_dentry(struct super_block *sb,
+ struct fid *fid, int fh_len, int fh_type)
+{
+ struct inode *inode;
+ struct dentry *dentry = ERR_PTR(-ENOENT);
+ unsigned long fhandle[2] = {fid->raw[0], fid->raw[1]};
+
+ if (fh_len < 2)
+ return NULL;
+
+ inode = cgroup_find_inode(fhandle, 1);
+ if (inode) {
+ dentry = d_find_alias(inode);
+ iput(inode);
+ }
+ return dentry;
+}
+
+static int cgroup_encode_fh(struct inode *inode, __u32 *fh, int *len,
+ struct inode *parent)
+{
+ if (*len < 2) {
+ *len = 2;
+ return FILEID_INVALID;
+ }
+
+ /*
+ * encode_fh is expected to return 255 (FILEID_INVALID)
+ * in case of failure. We can't return ENOMEM, so
+ * return FILEID_INVALID at least.
+ */
+ if (cgroup_hash_add(inode))
+ return FILEID_INVALID;
+
+ fh[0] = inode->i_generation;
+ fh[1] = inode->i_ino;
+ *len = 2;
+ return 1;
+}
+
+static const struct export_operations cgroup_export_ops = {
+ .encode_fh = cgroup_encode_fh,
+ .fh_to_dentry = cgroup_fh_to_dentry,
+};
+
+static int cgroup_delete_inode(struct inode *inode)
+{
+ cgroup_hash_del(inode);
+ return generic_delete_inode(inode);
+}
+
static const struct super_operations cgroup_ops = {
.statfs = simple_statfs,
- .drop_inode = generic_delete_inode,
+ .drop_inode = cgroup_delete_inode,
.show_options = cgroup_show_options,
#ifdef CONFIG_VE
.show_path = cgroup_show_path,
@@ -1539,6 +1704,7 @@ static int cgroup_set_super(struct super_block *sb, void *data)
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = CGROUP_SUPER_MAGIC;
sb->s_op = &cgroup_ops;
+ sb->s_export_op = &cgroup_export_ops;
return 0;
}
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