Re: block: sleeping in atomic warnings

On Tue, Feb 7, 2023 at 11:35 AM Eric Biggers [off-list ref] wrote:

The point of the "test_dummy_encryption" mount option is that you can just add
it to the mount options and run existing tests, such as a full run of xfstests,
and test all the encrypted I/O paths that way.  Which is extremely useful; it
wouldn't really be possible to properly test the encryption feature without it.

Yes, I see how useful that is, but:

Now, it's possible that "the kernel automatically adds the key for
test_dummy_encryption" could be implemented a bit differently.  It maybe could
be done at the last minute, when the key is being looked for due to a user
filesystem operation, instead of during the mount itself.

Yeah, that sounds like it would be the right solution, and get rid of
the fscrypt_destroy_keyring() case in __put_super().

Hmm.

I guess the filesystem only ever sees the '->get_tree()' call, and
then never gets any "this mount succeeded" callback.

And we do have at least that

        error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
        if (unlikely(error)) {
                fc_drop_locked(fc);
                return error;
        }

error case that does fc_drop_locked() -> deactivate_locked_super() ->
put_super().

Hmm. It does get "kill_sb()", if that happens, so if

 (a) the filesystem registers the keys late only in the success case

and

 (b) ->kill_sb() does the fscrypt_destroy_keyring(s)

then I *think* everything would be fine, and put_super() doesn't need to do it.

Or am I missing some case?

                Linus