From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
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: Thu, 9 Sep 2021 15:56:09 -0700 [thread overview]
Message-ID: <CAHk-=wi2fJ1XrgkfSYgn9atCzmJZ8J3HO5wnPO0Fvh5rQx9mmA@mail.gmail.com> (raw)
In-Reply-To: <ebb7b323-2ae9-9981-cdfd-f0f460be43b3@kernel.dk>
On Thu, Sep 9, 2021 at 3:21 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 9/9/21 3:56 PM, Linus Torvalds wrote:
> >
> > IOW, can't we have that
> >
> > ret = io_iter_do_read(req, iter);
> >
> > return partial success - and if XFS does that "update iovec on
> > failure", I could easily see that same code - or something else -
> > having done the exact same thing.
> >
> > Put another way: if the iovec isn't guaranteed to be coherent when an
> > actual error occurs, then why would it be guaranteed to be coherent
> > with a partial success value?
> >
> > Because in most cases - I'd argue pretty much all - those "partial
> > success" cases are *exactly* the same as the error cases, it's just
> > that we had a loop and one or more iterations succeeded before it hit
> > the error case.
>
> Right, which is why the reset would be nice, but reexpand + revert at
> least works and accomplishes the same even if it doesn't look as pretty.
You miss my point.
The partial success case seems to do the wrong thing.
Or am I misreading things? Lookie here, in io_read():
ret = io_iter_do_read(req, iter);
let's say that something succeeds partially, does X bytes, and returns
a positive X.
The if-statements following it then do not trigger:
if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
.. not this case ..
} else if (ret == -EIOCBQUEUED) {
.. nor this ..
} else if (ret <= 0 || ret == io_size || !force_nonblock ||
(req->flags & REQ_F_NOWAIT) || !(req->flags & REQ_F_ISREG)) {
.. nor this ..
}
so nothing has been done to the iovec at all.
Then it does
ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
using that iovec that has *not* been reset, even though it really
should have been reset to "X bytes read".
See what I'm trying to say?
Linus
next prev parent reply other threads:[~2021-09-09 22:56 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 [this message]
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
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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