From: NeilBrown <[email protected]> When filename_linkat() calls filename_create() which ultimately calls ->lookup, the flags LOOKUP_CREATE|LOOKUP_EXCL are passed. nfs_lookup() treats this as an exclusive create (which it is) and skips the ->lookup, leaving the dentry unchanged.
Currently that means nfs_link() can get a hashed dentry (if the name was already in the cache) or an unhashed dentry (if it wasn't). As none of d_add(), d_instantiate(), d_splice_alias() could handle both of these, nfs_link() calls d_drop() and then then d_add(). Recent changes to d_splice_alias() mean that it *can* work with either hashed or unhashed dentries. Future changes to locking mean that it will be unsafe to d_drop() a dentry while an operation (in this case "link()") is still ongoing. So change to use d_splice_alias(), and not to d_drop() until an error is detected (as in that case was can't be sure what is actually on the server). Also update the comment for nfs_is_exclusive_create() to note that link(), mkdir(), mknod(), symlink() all appear as exclusive creates. Those other than link() already used d_splice_alias() via nfs_add_or_obtain(). Signed-off-by: NeilBrown <[email protected]> --- fs/nfs/dir.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index 3033cc5ce12f..a188b09c9a54 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -1571,6 +1571,9 @@ static int nfs_check_verifier(struct inode *dir, struct dentry *dentry, /* * Use intent information to check whether or not we're going to do * an O_EXCL create using this path component. + * Note that link(), mkdir(), mknod(), symlink() all appear as + * exclusive creation. Regular file creation could be distinguished + * with LOOKUP_OPEN. */ static int nfs_is_exclusive_create(struct inode *dir, unsigned int flags) { @@ -2677,14 +2680,15 @@ nfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry) old_dentry, dentry); trace_nfs_link_enter(inode, dir, dentry); - d_drop(dentry); if (S_ISREG(inode->i_mode)) nfs_sync_inode(inode); error = NFS_PROTO(dir)->link(inode, dir, &dentry->d_name); if (error == 0) { nfs_set_verifier(dentry, nfs_save_change_attribute(dir)); ihold(inode); - d_add(dentry, inode); + d_splice_alias(inode, dentry); + } else { + d_drop(dentry); } trace_nfs_link_exit(inode, dir, dentry, error); return error; -- 2.50.0.107.gf914562f5916.dirty
