Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync

From	Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync
Date	2016-03-20 03:10 +0100
Message-ID	<reAYz-8a-13@gated-at.bofh.it> (permalink)
References	(6 earlier) <rcEjT-6Ns-11@gated-at.bofh.it> <reAlP-852-5@gated-at.bofh.it> <reAlP-852-7@gated-at.bofh.it> <reAFc-8cK-7@gated-at.bofh.it> <reAOT-8g3-15@gated-at.bofh.it>
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On Sat, Mar 19, 2016 at 6:55 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> What would make unlazy_walk() fail?  And if it succeeds, you are not
> in RCU mode anymore *without* restarting from scratch...

I don't see your point.

You don't want to be in RCU mode any more. You want to either succeed
or fail with ECHILD/ESTALE. Then, in the failure case, you go to the
thread.

What I meant by restarting was the restart that do_filp_open() does,
and there it just restarts with "op->lookup_flags", which has
RCU_LOOKUP still set, so it would just try to do the RCU lookup again.

But I actually notice now that Ben actually disabled that restart if
LOOKUP_RCU was set, so that ends up not even happening.

Anyway, I'm not saying it's polished and pretty. I think the changes
to do_filp_open() are a bit silly, and the code should just use
path_openat() directly. Possibly using a new helper (ie perhaps just
introduce a "rcu_filp_openat()" thing). But from a design perspective,
I think this all looks fine.

              Linus

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Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 02:30 +0100
  Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async  fsync Al Viro <viro@ZenIV.linux.org.uk> - 2016-03-20 02:30 +0100
    Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 02:50 +0100
      Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async  fsync Al Viro <viro@ZenIV.linux.org.uk> - 2016-03-20 03:00 +0100
        Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-20 03:10 +0100

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