On Fri, Dec 11, 2020 at 09:21:20AM -0800, Linus Torvalds wrote:
> On Fri, Dec 11, 2020 at 7:57 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >
> > On 12/10/20 7:35 PM, Al Viro wrote:
> > > _IF_ for some theoretical exercise you want to do "lookup without dropping
> > > out of RCU", just add a flag that has unlazy_walk() fail. With -ECHILD.
> > > Strip it away in complete_walk() and have path_init() with that flag
> > > and without LOOKUP_RCU fail with -EAGAIN. All there is to it.
> >
> > Thanks Al, that makes for an easier implementation. I like that suggestion,
> > boils it down to just three hunks (see below).
>
> Ooh. Yes, very nice.
Except for the wrong order in path_init() - the check should go _before_
if (!*s)
flags &= ~LOOKUP_RCU;
for obvious reasons.
Again, that part is trivial - what to do with do_open()/open_last_lookups()
is where the nastiness will be. Basically, it makes sure we bail out in
cases when lookup itself would've blocked, but it does *not* bail out
when equally heavy (and unlikely) blocking sources hit past the complete_walk().
Which makes it rather useless for the caller, unless we get logics added to
that part as well. And _that_ I want to see before we commit to anything.
