Re: [PATCH] Re: Possible FS race condition between iterate_dir and d_alloc_parallel

[Linus Torvalds <torvalds@linux-foundation.org>]

On Sat, Sep 21, 2019 at 7:07 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> FWIW, #next.dcache has the straight conversion to hlist.  It definitely
> wants at least nfsd, er... misconception dealt with, though: list_head
> or hlist, this

Well, yeah. But is there really any downside except for the warning?

Looks like the code should just do

                if (!simple_positive(dentry))
                        continue;

and just ignore non-positive dentries - whether cursors or negative
ones (which may not happen, but still).

> No "take cursors out of the list" parts yet.

Looking at the commits, that "take it off the list" one seems very
nice on its own. It actually seems to simplify the logic regardless of
the whole "don't need to add it to the end"..

Only this:

    if (next)
        list_move_tail(&cursor->d_child, &next->d_child);
    else
        list_del_init(&cursor->d_child);

is a slight complication, and honestly, I think that should just have
its own helper function there ("dcache_update_cursor(cursor, next)" or
something).

That helper function would end up meaning one less change in the hlist
conversion too.

The hlist conversion looks straightforward except for the list_move()
conversions that I didn't then look at more to make sure that they are
identical, but the ones I looked at looked sane.

              Linus