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.zhadche...@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; } -- 1.8.3.1 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
