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From: Jens Axboe <[email protected]>
To: Linus Torvalds <[email protected]>,
	Al Viro <[email protected]>
Cc: io-uring <[email protected]>,
	"[email protected]" <[email protected]>
Subject: Re: [GIT PULL] io_uring fixes for 5.10-rc
Date: Fri, 20 Nov 2020 19:41:30 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHk-=wimYoUtY4ygMNknkKZHqgYBZbkU4Koo5cE6ar8XjHkzGg@mail.gmail.com>

On 11/20/20 5:23 PM, Linus Torvalds wrote:
> On Fri, Nov 20, 2020 at 1:36 PM Jens Axboe <[email protected]> wrote:
>>
>> I don't disagree with you on that. I've been a bit gun shy on touching
>> the VFS side of things, but this one isn't too bad. I hacked up a patch
>> that allows io_uring to do LOOKUP_RCU and a quick test seems to indicate
>> it's fine. On top of that, we just propagate the error if we do fail and
>> get rid of that odd retry loop.
> 
> Ok, this looks better to me (but is obviously not 5.10 material).
> 
> That said, I think I'd prefer to keep 'struct nameidata' internal to
> just fs/namei.c, and maybe we can just expert that
> 
>         struct nameidata nd;
> 
>         set_nameidata(&nd, req->open.dfd, req->open.filename);
>         file = path_openat(&nd, &op, op.lookup_flags | LOOKUP_RCU);
>         restore_nameidata();
>         return filp == ERR_PTR(-ECHILD) ? -EAGAIN : filp;
> 
> as a helper from namei.c instead? Call it "do_filp_open_rcu()" or something?

Yes, that's probably a better idea. I'll move in that direction.

> That "force_nonblock" test seems a bit off, though. Why is that RCU
> case only done when "!force_nonblock"? It would seem that if
> force_nonblock is set, you want to do this too?

Taking a second look at it, it's inverted. So if force_nonblock == true,
we want to do just the RCU lookup.

But I think the bit that you're missing is that the other case will do
the normal lookup, which does an RCU lookup first. It looks needs to
look like this:

if (force_nonblock)
	file = do_filp_open_rcu();
else
	file = do_filp_open();

-- 
Jens Axboe


  reply	other threads:[~2020-11-21  2:41 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-20 18:45 [GIT PULL] io_uring fixes for 5.10-rc Jens Axboe
2020-11-20 20:02 ` Linus Torvalds
2020-11-20 21:36   ` Jens Axboe
2020-11-21  0:23     ` Linus Torvalds
2020-11-21  2:41       ` Jens Axboe [this message]
2020-11-21  3:00         ` Jens Axboe
2020-11-21 18:07           ` Linus Torvalds
2020-11-21 22:58             ` Jens Axboe
2020-12-10 17:32               ` namei.c LOOKUP_NONBLOCK (was "Re: [GIT PULL] io_uring fixes for 5.10-rc") Jens Axboe
2020-12-10 18:55                 ` Linus Torvalds
2020-12-10 19:21                   ` Jens Axboe
2020-11-21  0:29 ` [GIT PULL] io_uring fixes for 5.10-rc pr-tracker-bot
  -- strict thread matches above, loose matches on Subject: below --
2020-11-27 20:47 Jens Axboe
2020-11-27 21:21 ` pr-tracker-bot
2020-11-13 21:18 Jens Axboe
2020-11-14  0:15 ` pr-tracker-bot
2020-11-07 20:13 Jens Axboe
2020-11-07 22:08 ` pr-tracker-bot
2020-10-30 17:09 Jens Axboe
2020-10-30 22:10 ` pr-tracker-bot

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