Except for two small nits it looks good.
Note: Because we use atomic_inc_not_zero(i_count) and the fact that iput
can increment i_count back, we can _potentially_ see situation that
open_by_handle_at first fails to open and next is able to open the same
handle. But I don't think it's a big deal for us.
On 7/28/20 2:59 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.
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.
https://jira.sw.ru/browse/PSBM-105889
Signed-off-by: Andrey Zhadchenko <andrey.zhadche...@virtuozzo.com>
---
kernel/cgroup.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 136 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9fdba79..267a5a4 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/time.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 = get_seconds();
We likely want to use prandom_u32() instead, see mainstream linux commit
46c9a946d766 ("shmem: use monotonic time for i_generation"), they've
change it for shmem to overcome overflow.
inode->i_mode = mode;
inode->i_uid = current_fsuid();
inode->i_gid = current_fsgid();
@@ -1390,9 +1393,140 @@ 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_inode(unsigned long fhandle[2],
+ char take_ref)
+{
+ struct cg_inode_hitem *i;
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(fhandle[1]);
+ struct cg_inode_hitem *found = NULL;
+
+ spin_lock(&cgroup_inode_table_lock);
+ hlist_for_each_entry(i, head, hlist) {
+ if (i->inode->i_generation == fhandle[0] &&
+ i->inode->i_ino == fhandle[1]) {
+ /*
+ * 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_find_inode. 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)
+ if (!atomic_inc_not_zero(&i->inode->i_count))
+ continue;
Should be break instead of continue? There can't be another entry in
hash with same i_ino and i_generation.
+ found = i;
+ break;
+ }
+ }
+ spin_unlock(&cgroup_inode_table_lock);
+
+ 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);
+ unsigned long fhandle[2] = {fid->raw[0], fid->raw[1]};
+
+ if (fh_len < 2)
+ return NULL;
+
+ item = cgroup_find_inode(fhandle, 1);
+ if (item) {
+ dentry = d_find_alias(item->inode);
+ iput(item->inode);
+ }
+ return dentry;
+}
+
+static int cgroup_encode_fh(struct inode *inode, __u32 *fh, int *len,
+ struct inode *parent)
+{
+ struct cg_inode_hitem *item;
+ struct hlist_head *head = cgroup_inode_table
+ + cgroup_inode_get_hash(inode->i_ino);
+ unsigned long fhandle[2] = {inode->i_generation, inode->i_ino};
+
+ if (*len < 2) {
+ *len = 2;
+ return FILEID_INVALID;
+ }
+
+ if (!cgroup_find_inode(fhandle, 0)) {
+ 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] = fhandle[0];
+ fh[1] = fhandle[1];
+ *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)
+{
+ struct cg_inode_hitem *item = NULL;
+ unsigned long fhandle[2] = {inode->i_generation, inode->i_ino};
+
+ item = cgroup_find_inode(fhandle, 0);
+ 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 +1673,7 @@ 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;
}
--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.
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