Message-ID: <ea6eef767ae6bcdf7aeae7bbc00c2dd89f8c7e5f.camel@kernel.org>
Date:   Mon, 16 May 2022 09:23:12 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Xiubo Li <xiubli@...hat.com>, viro@...iv.linux.org.uk
Cc:     idryomov@...il.com, vshankar@...hat.com,
        ceph-devel@...r.kernel.org, mcgrof@...nel.org,
        akpm@...ux-foundation.org, arnd@...db.de,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ceph: wait the first reply of inflight unlink/rmdir

On Mon, 2022-05-16 at 20:20 +0800, Xiubo Li wrote:
> In async unlink case the kclient won't wait for the first reply
> from MDS and just drop all the links and unhash the dentry and then
> succeeds immediately.
> 
> For any new create/link/rename,etc requests followed by using the
> same file names we must wait for the first reply of the inflight
> unlink request, or the MDS possibly will fail these following
> requests with -EEXIST if the inflight async unlink request was
> delayed for some reasons.
> 
> And the worst case is that for the none async openc request it will
> successfully open the file if the CDentry hasn't been unlinked yet,
> but later the previous delayed async unlink request will remove the
> CDenty. That means the just created file is possiblly deleted later
> by accident.
> 
> We need to wait for the inflight async unlink requests to finish
> when creating new files/directories by using the same file names.
> 
> URL: https://tracker.ceph.com/issues/55332
> Signed-off-by: Xiubo Li <xiubli@...hat.com>
> ---
>  fs/ceph/dir.c        | 55 +++++++++++++++++++++++++++++++----
>  fs/ceph/file.c       |  5 ++++
>  fs/ceph/mds_client.c | 69 ++++++++++++++++++++++++++++++++++++++++++++
>  fs/ceph/mds_client.h |  1 +
>  fs/ceph/super.c      |  2 ++
>  fs/ceph/super.h      | 18 ++++++++----
>  6 files changed, 140 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> index eae417d71136..20c648406528 100644
> --- a/fs/ceph/dir.c
> +++ b/fs/ceph/dir.c
> @@ -856,6 +856,10 @@ static int ceph_mknod(struct user_namespace *mnt_userns, struct inode *dir,
>  	if (ceph_snap(dir) != CEPH_NOSNAP)
>  		return -EROFS;
>  
> +	err = ceph_wait_on_conflict_unlink(dentry);
> +	if (err)
> +		return err;
> +
>  	if (ceph_quota_is_max_files_exceeded(dir)) {
>  		err = -EDQUOT;
>  		goto out;
> @@ -918,6 +922,10 @@ static int ceph_symlink(struct user_namespace *mnt_userns, struct inode *dir,
>  	if (ceph_snap(dir) != CEPH_NOSNAP)
>  		return -EROFS;
>  
> +	err = ceph_wait_on_conflict_unlink(dentry);
> +	if (err)
> +		return err;
> +
>  	if (ceph_quota_is_max_files_exceeded(dir)) {
>  		err = -EDQUOT;
>  		goto out;
> @@ -968,9 +976,13 @@ static int ceph_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
>  	struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(dir->i_sb);
>  	struct ceph_mds_request *req;
>  	struct ceph_acl_sec_ctx as_ctx = {};
> -	int err = -EROFS;
> +	int err;
>  	int op;
>  
> +	err = ceph_wait_on_conflict_unlink(dentry);
> +	if (err)
> +		return err;
> +
>  	if (ceph_snap(dir) == CEPH_SNAPDIR) {
>  		/* mkdir .snap/foo is a MKSNAP */
>  		op = CEPH_MDS_OP_MKSNAP;
> @@ -980,6 +992,7 @@ static int ceph_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
>  		dout("mkdir dir %p dn %p mode 0%ho\n", dir, dentry, mode);
>  		op = CEPH_MDS_OP_MKDIR;
>  	} else {
> +		err = -EROFS;
>  		goto out;
>  	}
>  
> @@ -1037,6 +1050,10 @@ static int ceph_link(struct dentry *old_dentry, struct inode *dir,
>  	struct ceph_mds_request *req;
>  	int err;
>  
> +	err = ceph_wait_on_conflict_unlink(dentry);
> +	if (err)
> +		return err;
> +
>  	if (ceph_snap(dir) != CEPH_NOSNAP)
>  		return -EROFS;
>  
> @@ -1071,9 +1088,24 @@ static int ceph_link(struct dentry *old_dentry, struct inode *dir,
>  static void ceph_async_unlink_cb(struct ceph_mds_client *mdsc,
>  				 struct ceph_mds_request *req)
>  {
> +	struct dentry *dentry = req->r_dentry;
> +	struct ceph_dentry_info *di = ceph_dentry(dentry);
>  	int result = req->r_err ? req->r_err :
>  			le32_to_cpu(req->r_reply_info.head->result);
>  
> +	if (test_bit(CEPH_DENTRY_ASYNC_UNLINK_BIT, &di->flags)) {
> +		BUG_ON(req->r_op != CEPH_MDS_OP_UNLINK);
> +
> +		hash_del_rcu(&di->hnode);
> +
> +		spin_lock(&dentry->d_lock);
> +		di->flags &= ~CEPH_DENTRY_ASYNC_UNLINK;
> +		wake_up_bit(&di->flags, CEPH_DENTRY_ASYNC_UNLINK_BIT);
> +		spin_unlock(&dentry->d_lock);
> +
> +		synchronize_rcu();
> +	}
> +
>  	if (result == -EJUKEBOX)
>  		goto out;
>  
> @@ -1081,7 +1113,7 @@ static void ceph_async_unlink_cb(struct ceph_mds_client *mdsc,
>  	if (result) {
>  		int pathlen = 0;
>  		u64 base = 0;
> -		char *path = ceph_mdsc_build_path(req->r_dentry, &pathlen,
> +		char *path = ceph_mdsc_build_path(dentry, &pathlen,
>  						  &base, 0);
>  
>  		/* mark error on parent + clear complete */
> @@ -1089,13 +1121,13 @@ static void ceph_async_unlink_cb(struct ceph_mds_client *mdsc,
>  		ceph_dir_clear_complete(req->r_parent);
>  
>  		/* drop the dentry -- we don't know its status */
> -		if (!d_unhashed(req->r_dentry))
> -			d_drop(req->r_dentry);
> +		if (!d_unhashed(dentry))
> +			d_drop(dentry);
>  
>  		/* mark inode itself for an error (since metadata is bogus) */
>  		mapping_set_error(req->r_old_inode->i_mapping, result);
>  
> -		pr_warn("ceph: async unlink failure path=(%llx)%s result=%d!\n",
> +		pr_warn("async unlink failure path=(%llx)%s result=%d!\n",
>  			base, IS_ERR(path) ? "<<bad>>" : path, result);
>  		ceph_mdsc_free_path(path, pathlen);
>  	}
> @@ -1189,12 +1221,21 @@ static int ceph_unlink(struct inode *dir, struct dentry *dentry)
>  		ihold(req->r_old_inode);
>  		err = ceph_mdsc_submit_request(mdsc, dir, req);
>  		if (!err) {
> +			struct ceph_dentry_info *di;
> +
>  			/*
>  			 * We have enough caps, so we assume that the unlink
>  			 * will succeed. Fix up the target inode and dcache.
>  			 */
>  			drop_nlink(inode);
>  			d_delete(dentry);
> +
> +			spin_lock(&dentry->d_lock);
> +			di = ceph_dentry(dentry);
> +			di->flags |= CEPH_DENTRY_ASYNC_UNLINK;
> +			hash_add_rcu(fsc->async_unlink_conflict, &di->hnode,
> +				     dentry->d_name.hash);
> +			spin_unlock(&dentry->d_lock);

This looks racy. It's possible that the reply comes in before we get to
the point of setting this flag. You probably want to do this before
calling ceph_mdsc_submit_request, and just unwind it if the submission
fails.


Also, you do still need some sort of lock to protect the
hash_add/del/_rcu calls. Those don't do any locking on their own. The
d_lock is insufficient here since it can't protect the whole list. You
may be able to use the i_ceph_lock of the parent though?

>  		} else if (err == -EJUKEBOX) {
>  			try_async = false;
>  			ceph_mdsc_put_request(req);
> @@ -1237,6 +1278,10 @@ static int ceph_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
>  	    (!ceph_quota_is_same_realm(old_dir, new_dir)))
>  		return -EXDEV;
>  
> +	err = ceph_wait_on_conflict_unlink(new_dentry);
> +	if (err)
> +		return err;
> +
>  	dout("rename dir %p dentry %p to dir %p dentry %p\n",
>  	     old_dir, old_dentry, new_dir, new_dentry);
>  	req = ceph_mdsc_create_request(mdsc, op, USE_AUTH_MDS);
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 8c8226c0feac..47d068e6436a 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -740,6 +740,10 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
>  	if (dentry->d_name.len > NAME_MAX)
>  		return -ENAMETOOLONG;
>  
> +	err = ceph_wait_on_conflict_unlink(dentry);
> +	if (err)
> +		return err;
> +

What might be nice here eventually is to not block an async create here,
but instead queue the request so that it gets transmitted after the
async unlink reply comes in.

That'll be hard to get right though, so this is fine for now.

>  	if (flags & O_CREAT) {
>  		if (ceph_quota_is_max_files_exceeded(dir))
>  			return -EDQUOT;
> @@ -757,6 +761,7 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
>  		/* If it's not being looked up, it's negative */
>  		return -ENOENT;
>  	}
> +
>  retry:
>  	/* do the open */
>  	req = prepare_open_request(dir->i_sb, flags, mode);
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index e8c87dea0551..0ae0e0110eb4 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -468,6 +468,75 @@ static int ceph_parse_deleg_inos(void **p, void *end,
>  	return -EIO;
>  }
>  
> +/*
> + * In async unlink case the kclient won't wait for the first reply
> + * from MDS and just drop all the links and unhash the dentry and then
> + * succeeds immediately.
> + *
> + * For any new create/link/rename,etc requests followed by using the
> + * same file names we must wait for the first reply of the inflight
> + * unlink request, or the MDS possibly will fail these following
> + * requests with -EEXIST if the inflight async unlink request was
> + * delayed for some reasons.
> + *
> + * And the worst case is that for the none async openc request it will
> + * successfully open the file if the CDentry hasn't been unlinked yet,
> + * but later the previous delayed async unlink request will remove the
> + * CDenty. That means the just created file is possiblly deleted later
> + * by accident.
> + *
> + * We need to wait for the inflight async unlink requests to finish
> + * when creating new files/directories by using the same file names.
> + */
> +int ceph_wait_on_conflict_unlink(struct dentry *dentry)
> +{
> +	struct ceph_fs_client *fsc = ceph_sb_to_client(dentry->d_sb);
> +	struct dentry *pdentry = dentry->d_parent;
> +	struct dentry *udentry, *found = NULL;
> +	struct ceph_dentry_info *di;
> +	struct qstr dname;
> +	u32 hash = dentry->d_name.hash;
> +	int err;
> +
> +	dname.name = dentry->d_name.name;
> +	dname.len = dentry->d_name.len;
> +
> +	rcu_read_lock();
> +	hash_for_each_possible_rcu(fsc->async_unlink_conflict, di,
> +				   hnode, hash) {
> +		udentry = di->dentry;
> +
> +		spin_lock(&udentry->d_lock);
> +		if (udentry->d_name.hash != hash)
> +			goto next;
> +		if (unlikely(udentry->d_parent != pdentry))
> +			goto next;
> +		if (!hash_hashed(&di->hnode))
> +			goto next;
> +
> +		if (!test_bit(CEPH_DENTRY_ASYNC_UNLINK_BIT, &di->flags))
> +			goto next;
> +

Maybe this should be a warning? Will we ever have entries in this
hashtable that don't have this bit set?

> +		if (d_compare(pdentry, udentry, &dname))
> +			goto next;
> +
> +		spin_unlock(&udentry->d_lock);
> +		found = dget(udentry);
> +		break;
> +next:
> +		spin_unlock(&udentry->d_lock);
> +	}
> +	rcu_read_unlock();
> +
> +	if (likely(!found))
> +		return 0;
> +
> +	err = wait_on_bit(&di->flags, CEPH_DENTRY_ASYNC_UNLINK_BIT,
> +			  TASK_INTERRUPTIBLE);
> +	dput(found);
> +	return err;
> +}
> +
>  u64 ceph_get_deleg_ino(struct ceph_mds_session *s)
>  {
>  	unsigned long ino;
> diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
> index 33497846e47e..d1ae679c52c3 100644
> --- a/fs/ceph/mds_client.h
> +++ b/fs/ceph/mds_client.h
> @@ -582,6 +582,7 @@ static inline int ceph_wait_on_async_create(struct inode *inode)
>  			   TASK_INTERRUPTIBLE);
>  }
>  
> +extern int ceph_wait_on_conflict_unlink(struct dentry *dentry);
>  extern u64 ceph_get_deleg_ino(struct ceph_mds_session *session);
>  extern int ceph_restore_deleg_ino(struct ceph_mds_session *session, u64 ino);
>  #endif
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index b73b4f75462c..7ae65001f04c 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -816,6 +816,8 @@ static struct ceph_fs_client *create_fs_client(struct ceph_mount_options *fsopt,
>  	if (!fsc->cap_wq)
>  		goto fail_inode_wq;
>  
> +	hash_init(fsc->async_unlink_conflict);
> +
>  	spin_lock(&ceph_fsc_lock);
>  	list_add_tail(&fsc->metric_wakeup, &ceph_fsc_list);
>  	spin_unlock(&ceph_fsc_lock);
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index 506d52633627..58bbb5df42da 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -19,6 +19,7 @@
>  #include <linux/security.h>
>  #include <linux/netfs.h>
>  #include <linux/fscache.h>
> +#include <linux/hashtable.h>
>  
>  #include <linux/ceph/libceph.h>
>  
> @@ -99,6 +100,8 @@ struct ceph_mount_options {
>  	char *mon_addr;
>  };
>  
> +#define CEPH_ASYNC_CREATE_CONFLICT_BITS 12
> +
>  struct ceph_fs_client {
>  	struct super_block *sb;
>  
> @@ -124,6 +127,8 @@ struct ceph_fs_client {
>  	struct workqueue_struct *inode_wq;
>  	struct workqueue_struct *cap_wq;
>  
> +	DECLARE_HASHTABLE(async_unlink_conflict, CEPH_ASYNC_CREATE_CONFLICT_BITS);
> +
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *debugfs_dentry_lru, *debugfs_caps;
>  	struct dentry *debugfs_congestion_kb;
> @@ -281,7 +286,8 @@ struct ceph_dentry_info {
>  	struct dentry *dentry;
>  	struct ceph_mds_session *lease_session;
>  	struct list_head lease_list;
> -	unsigned flags;
> +	struct hlist_node hnode;
> +	unsigned long flags;
>  	int lease_shared_gen;
>  	u32 lease_gen;
>  	u32 lease_seq;
> @@ -290,10 +296,12 @@ struct ceph_dentry_info {
>  	u64 offset;
>  };
>  
> -#define CEPH_DENTRY_REFERENCED		1
> -#define CEPH_DENTRY_LEASE_LIST		2
> -#define CEPH_DENTRY_SHRINK_LIST		4
> -#define CEPH_DENTRY_PRIMARY_LINK	8
> +#define CEPH_DENTRY_REFERENCED		(1 << 0)
> +#define CEPH_DENTRY_LEASE_LIST		(1 << 1)
> +#define CEPH_DENTRY_SHRINK_LIST		(1 << 2)
> +#define CEPH_DENTRY_PRIMARY_LINK	(1 << 3)
> +#define CEPH_DENTRY_ASYNC_UNLINK_BIT	(4)
> +#define CEPH_DENTRY_ASYNC_UNLINK	(1 << CEPH_DENTRY_ASYNC_UNLINK_BIT)
>  
>  struct ceph_inode_xattrs_info {
>  	/*

-- 
Jeff Layton <jlayton@...nel.org>

Powered by blists - more mailing lists