Messages in this thread | | | Subject | Re: [PATCH 2/2] ceph: wait the first reply of inflight unlink/rmdir | From | Xiubo Li <> | Date | Mon, 16 May 2022 22:56:49 +0800 |
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On 5/16/22 9:23 PM, Jeff Layton wrote: > 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@redhat.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.
Ah, right. Will fix it.
> > Also, you do still need some sort of lock to protect the > hash_add/del/_rcu calls.
Sure, will fix it too.
> 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?
The hashtable is a global one, so we couldn't use the i_ceph_lock here. I will add one dedicated spin lock for each sb.
>> } 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.
Sure.
> >> 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?
Just before we take "spin_lock(&udentry->d_lock)" the udentry could be already removed from hashtable and the bit was cleared ?
-- Xiubo
> >> + 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 { >> /*
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