linux-ext4 - Re: fun with d_invalidate() vs. d_splice_alias() was Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs

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Date: Mon, 27 Nov 2023 10:01:34 -0600
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Gabriel Krisman Bertazi <gabriel@...sman.be>,  Linus Torvalds
 <torvalds@...ux-foundation.org>,  Christian Brauner <brauner@...nel.org>,
  tytso@....edu,  linux-f2fs-devel@...ts.sourceforge.net,
  ebiggers@...nel.org,  linux-fsdevel@...r.kernel.org,  jaegeuk@...nel.org,
  linux-ext4@...r.kernel.org,  Miklos Szeredi <miklos@...redi.hu>
Subject: Re: fun with d_invalidate() vs. d_splice_alias() was Re: [f2fs-dev]
 [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs

"Eric W. Biederman" <ebiederm@...ssion.com> writes:

> I am confused what is going on with ext4 and f2fs.  I think they
> are calling d_invalidate when all they need to call is d_drop.

ext4 and f2f2 are buggy in how they call d_invalidate, if I am reading
the code correctly.

d_invalidate calls detach_mounts.

detach_mounts relies on setting D_CANT_MOUNT on the top level dentry to
prevent races with new mounts.

ext4 and f2fs (in their case insensitive code) are calling d_invalidate
before dont_mount has been called to set D_CANT_MOUNT.

Eric