On Wed, Aug 07, 2024 at 07:23:00AM +0100, Al Viro wrote: > After having looked at the problem, how about the following > series: > > 1/5) lift path_get() *AND* path_put() out of do_dentry_open() > into the callers. The latter - conditional upon "do_dentry_open() > has not set FMODE_OPENED". Equivalent transformation. > > 2/5) move path_get() we'd lifted into the callers past the > call of do_dentry_open(), conditionally collapse it with path_put(). > You'd get e.g. > int vfs_open(const struct path *path, struct file *file) > { > int ret; > > file->f_path = *path; > ret = do_dentry_open(file, NULL); > if (!ret) { > /* > * Once we return a file with FMODE_OPENED, __fput() will call > * fsnotify_close(), so we need fsnotify_open() here for > * symmetry. > */ > fsnotify_open(file); > } > if (file->f_mode & FMODE_OPENED) > path_get(path); > return ret; > } > > Equivalent transformation, provided that nobody is playing silly > buggers with reassigning ->f_path in their ->open() instances. > They *really* should not - if anyone does, we'd better catch them > and fix them^Wtheir code. Incidentally, if we find any such, > we have a damn good reason to add asserts in the callers. As > in, "if do_dentry_open() has set FMODE_OPENED, it would bloody > better *not* modify ->f_path". <greps> Nope, nobody is that > insane. > > 3/5) split vfs_open_consume() out of vfs_open() (possibly > named vfs_open_borrow()), replace the call in do_open() with > calling the new function. > > Trivially equivalent transformation. > > 4/5) Remove conditional path_get() from vfs_open_consume() > and finish_open(). Add > if (file->f_mode & FMODE_OPENED) > path_get(&nd->path); > before terminate_walk(nd); in path_openat(). > > Equivalent transformation - see > if (file->f_mode & (FMODE_OPENED | FMODE_CREATED)) { > dput(nd->path.dentry); > nd->path.dentry = dentry; > return NULL; > } > in lookup_open() (which is where nd->path gets in sync with what > had been given to do_dentry_open() in finish_open()); in case > of vfs_open_consume() in do_open() it's in sync from the very > beginning. And we never modify nd->path after those points. > So we can move grabbing it downstream, keeping it under the > same condition (which also happens to be true only if we'd > called do_dentry_open(), so for all other paths through the > whole thing it's a no-op. > > 5/5) replace > if (file->f_mode & FMODE_OPENED) > path_get(&nd->path); > terminate_walk(nd); > with > if (file->f_mode & FMODE_OPENED) { > nd->path.mnt = NULL; > nd->path.dentry = NULL; > } > terminate_walk(nd); > Again, an obvious equivalent transformation. BTW, similar to that, with that we could turn do_o_path() into struct path path; int error = path_lookupat(nd, flags, &path); if (!error) { audit_inode(nd->name, path.dentry, 0); error = vfs_open_borrow(&path, file); if (!(file->f_mode & FMODE_OPENED)) path_put(&path); } return error; } and perhaps do something similar in the vicinity of vfs_tmpfile() / do_o_tmpfile().