On Wed, Aug 7, 2024 at 8:33 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > 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(). That's quite a bit of churn, but if you insist I can take a stab. fwiw I do think the weird error condition in do_dentry_open can be used to simplify stuff, which I still do in my v2. with my approach there is never a path_put needed to backpedal (it was already done by do_dentry_open *or* it is going to be done by whoever doing last fput) then do_o_path would be: struct path path; int error = path_lookupat(nd, flags, &path); if (!error) { audit_inode(nd->name, path.dentry, 0); error = vfs_open_consume(&path, file); } return error; -- Mateusz Guzik <mjguzik gmail.com>