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From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Pavel Begunkov <asml.silence@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [git pull] iov_iter fixes
Date: Fri, 10 Sep 2021 03:15:35 +0000	[thread overview]
Message-ID: <YTrN16wu/KE0X/QZ@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <8d9e4f7c-bcf4-2751-9978-6283cabeda52@kernel.dk>

On Thu, Sep 09, 2021 at 09:06:58PM -0600, Jens Axboe wrote:
> On 9/9/21 8:48 PM, Al Viro wrote:
> > On Thu, Sep 09, 2021 at 07:35:13PM -0600, Jens Axboe wrote:
> > 
> >> Yep ok I follow you now. And yes, if we get a partial one but one that
> >> has more consumed than what was returned, that would not work well. I'm
> >> guessing that a) we've never seen that, or b) we always end up with
> >> either correctly advanced OR fully advanced, and the fully advanced case
> >> would then just return 0 next time and we'd just get a short IO back to
> >> userspace.
> >>
> >> The safer way here would likely be to import the iovec again. We're
> >> still in the context of the original submission, and the sqe hasn't been
> >> consumed in the ring yet, so that can be done safely.
> > 
> > ... until you end up with something assuming that you've got the same
> > iovec from userland the second time around.
> > 
> > IOW, generally it's a bad idea to do that kind of re-imports.
> 
> That's really no different than having one thread do the issue, and
> another modify the iovec while it happens. It's only an issue if you
> don't validate it, just like you did the first time you imported. No
> assumptions need to be made here.

	It's not "need to be made", it's "will be mistakenly made by
somebody several years down the road"...

  reply	other threads:[~2021-09-10  3:15 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-09  4:22 [git pull] iov_iter fixes Al Viro
2021-09-09 19:37 ` Linus Torvalds
2021-09-09 21:19   ` Jens Axboe
2021-09-09 21:39     ` Jens Axboe
2021-09-09 21:56       ` Linus Torvalds
2021-09-09 22:21         ` Jens Axboe
2021-09-09 22:56           ` Linus Torvalds
2021-09-10  1:35             ` Jens Axboe
2021-09-10  2:43               ` Jens Axboe
2021-09-10  2:48               ` Al Viro
2021-09-10  3:06                 ` Jens Axboe
2021-09-10  3:15                   ` Al Viro [this message]
2021-09-10  3:23                     ` Jens Axboe
2021-09-10  3:24                     ` Al Viro
2021-09-10  3:28                       ` Jens Axboe
2021-09-13 15:29                 ` David Laight
2021-09-09 21:42     ` Dave Chinner
2021-09-10  2:57     ` Al Viro
2021-09-10  3:05       ` Jens Axboe
2021-09-10  3:11         ` Al Viro
2021-09-10  3:22           ` Jens Axboe
2021-09-10  3:27             ` Al Viro
2021-09-10  3:30               ` Jens Axboe
2021-09-10  3:36                 ` Al Viro
2021-09-10 13:57                   ` Jens Axboe
2021-09-10 14:42                     ` Al Viro
2021-09-10 15:08                       ` Jens Axboe
2021-09-10 15:32                         ` Al Viro
2021-09-10 15:36                           ` Jens Axboe
2021-09-10 15:04                     ` Jens Axboe
2021-09-10 16:06                       ` Jens Axboe
2021-09-10 16:44                         ` Linus Torvalds
2021-09-10 16:56                         ` Al Viro
2021-09-10 16:58                           ` Linus Torvalds
2021-09-10 17:26                             ` Jens Axboe
2021-09-10 17:31                               ` Linus Torvalds
2021-09-10 17:32                                 ` Jens Axboe
2021-09-10 18:48                                 ` Al Viro
2021-09-10 19:04                                   ` Linus Torvalds
2021-09-10 19:10                                     ` Linus Torvalds
2021-09-10 19:10                                   ` Jens Axboe
2021-09-10 17:04                           ` Jens Axboe
2021-09-09 22:54   ` Pavel Begunkov
2021-09-09 22:57     ` Pavel Begunkov
2021-09-09 23:14   ` Pavel Begunkov
2021-09-09 20:03 ` pr-tracker-bot

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