From c54b386969a58151765a9ffaaa0438e7b580283f Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Thu, 27 Feb 2025 12:32:58 +1100 Subject: VFS: Change vfs_mkdir() to return the dentry. vfs_mkdir() does not guarantee to leave the child dentry hashed or make it positive on success, and in many such cases the filesystem had to use a different dentry which it can now return. This patch changes vfs_mkdir() to return the dentry provided by the filesystems which is hashed and positive when provided. This reduces the number of cases where the resulting dentry is not positive to a handful which don't deserve extra efforts. The only callers of vfs_mkdir() which are interested in the resulting inode are in-kernel filesystem clients: cachefiles, nfsd, smb/server. The only filesystems that don't reliably provide the inode are: - kernfs, tracefs which these clients are unlikely to be interested in - cifs in some configurations would need to do a lookup to find the created inode, but doesn't. cifs cannot be exported via NFS, is unlikely to be used by cachefiles, and smb/server only has a soft requirement for the inode, so this is unlikely to be a problem in practice. - hostfs, nfs, cifs may need to do a lookup (rarely for NFS) and it is possible for a race to make that lookup fail. Actual failure is unlikely and providing callers handle negative dentries graceful they will fail-safe. So this patch removes the lookup code in nfsd and smb/server and adjusts them to fail safe if a negative dentry is provided: - cache-files already fails safe by restarting the task from the top - it still does with this change, though it no longer calls cachefiles_put_directory() as that will crash if the dentry is negative. - nfsd reports "Server-fault" which it what it used to do if the lookup failed. This will never happen on any file-systems that it can actually export, so this is of no consequence. I removed the fh_update() call as that is not needed and out-of-place. A subsequent nfsd_create_setattr() call will call fh_update() when needed. - smb/server only wants the inode to call ksmbd_smb_inherit_owner() which updates ->i_uid (without calling notify_change() or similar) which can be safely skipping on cifs (I hope). If a different dentry is returned, the first one is put. If necessary the fact that it is new can be determined by comparing pointers. A new dentry will certainly have a new pointer (as the old is put after the new is obtained). Similarly if an error is returned (via ERR_PTR()) the original dentry is put. Reviewed-by: Jeff Layton Signed-off-by: NeilBrown Link: https://lore.kernel.org/r/20250227013949.536172-7-neilb@suse.de Signed-off-by: Christian Brauner --- fs/cachefiles/namei.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) (limited to 'fs/cachefiles') diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c index 7cf59713f0f7..83a60126de0f 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -128,18 +128,19 @@ retry: ret = security_path_mkdir(&path, subdir, 0700); if (ret < 0) goto mkdir_error; - ret = cachefiles_inject_write_error(); - if (ret == 0) - ret = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700); - if (ret < 0) { + subdir = ERR_PTR(cachefiles_inject_write_error()); + if (!IS_ERR(subdir)) + subdir = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700); + ret = PTR_ERR(subdir); + if (IS_ERR(subdir)) { trace_cachefiles_vfs_error(NULL, d_inode(dir), ret, cachefiles_trace_mkdir_error); goto mkdir_error; } trace_cachefiles_mkdir(dir, subdir); - if (unlikely(d_unhashed(subdir))) { - cachefiles_put_directory(subdir); + if (unlikely(d_unhashed(subdir) || d_is_negative(subdir))) { + dput(subdir); goto retry; } ASSERT(d_backing_inode(subdir)); @@ -195,7 +196,8 @@ mark_error: mkdir_error: inode_unlock(d_inode(dir)); - dput(subdir); + if (!IS_ERR(subdir)) + dput(subdir); pr_err("mkdir %s failed with error %d\n", dirname, ret); return ERR_PTR(ret); -- cgit v1.2.3