On 7/24/20 6:50 PM, Andrey Zhadchenko wrote:
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.
https://jira.sw.ru/browse/PSBM-105889
Signed-off-by: Andrey Zhadchenko <andrey.zhadche...@virtuozzo.com>
---
kernel/cgroup.c | 112
+++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 111 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9fdba79..a459c56 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -62,6 +62,7 @@
#include <linux/kthread.h>
#include <linux/ve.h>
#include <linux/stacktrace.h>
+#include <linux/exportfs.h>
#include <linux/atomic.h>
@@ -1390,9 +1391,117 @@ 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_inode_hash_find(unsigned int i_ino)
+{
+ struct cg_inode_hitem *i;
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(i_ino);
+ struct cg_inode_hitem *found = 0;
NULL would look better than 0 for pointer.
+
+ spin_lock(&cgroup_inode_table_lock);
+ hlist_for_each_entry(i, head, hlist) {
+ if (i->inode->i_ino == i_ino) {
+ found = i;
+ break;
+ }
+ }
+ spin_unlock(&cgroup_inode_table_lock);
The cg_inode_hitem can be freed from other thread just after you release
the lock. Inode can be evicted and freed just after you release the
lock. We should iget a reference on inode before releasing lock and
return inode instead of cg_inode_hitem.
+
+ return found;
+}
+
+static struct dentry *cgroup_fh_to_dentry(struct super_block *sb,
+ struct fid *fid, int fh_len, int fh_type)
+{
+ struct cg_inode_hitem *item;
+ struct dentry *dentry = ERR_PTR(-ENOENT);
+
+ if (fh_len < 1)
+ return NULL;
+
+ item = cgroup_inode_hash_find(fid->raw[0]);
+ if (item)
+ dentry = d_find_alias(item->inode);
When you've got dentry you can put the inode reference back. See how
it's done in shmem_fh_to_dentry.
+
+ return dentry;
+}
+
+static int cgroup_encode_fh(struct inode *inode, __u32 *fh, int *len,
+ struct inode *parent)
+{
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(inode->i_ino);
+ struct cg_inode_hitem *item;
+
+ if (*len < 1) {
+ *len = 1;
+ return FILEID_INVALID;
+ }
+
+ if (cgroup_inode_hash_find(inode->i_ino) == 0) {
Would look better:
if (!cgroup_inode_hash_find(inode->i_ino)) {
+ item = kmalloc(sizeof(struct cg_inode_hitem),
+ GFP_KERNEL);
+ /*
+ * 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 (!item)
+ return FILEID_INVALID;
+ item->inode = inode;
+
+ spin_lock(&cgroup_inode_table_lock);
+ hlist_add_head(&item->hlist, head);
+ spin_unlock(&cgroup_inode_table_lock);
+ }
+
+ fh[0] = inode->i_ino;
+ *len = 1;
+ 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)
+{
+ struct cg_inode_hitem *item = cgroup_inode_hash_find(inode->i_ino);
I don't like this. Lets only merge variable initialization and
declaration if You don't expect any fail. And put empty line between
declaration and everything else.
+ if (item) {
+ spin_lock(&cgroup_inode_table_lock);
+ hlist_del(&item->hlist);
+ spin_unlock(&cgroup_inode_table_lock);
+
+ kfree(item);
+ }
+
+ 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 +1648,7 @@ 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;
}
