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From: Jens Axboe <axboe@kernel.dk>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Pavel Begunkov <asml.silence@gmail.com>
Cc: 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 15:39:15 -0600	[thread overview]
Message-ID: <ebc6cc5e-dd43-6370-b462-228e142beacb@kernel.dk> (raw)
In-Reply-To: <5971af96-78b7-8304-3e25-00dc2da3c538@kernel.dk>

On 9/9/21 3:19 PM, Jens Axboe wrote:
>> That "req->result" is once again the *original* length, and the above
>> code once again mis-handles the case of "oh, the iov got truncated
>> because of some IO limit".
>>
>> So I've pulled this, but I think it is
>>
>>  (a) ugly nasty
>>
>>  (b) incomplete and misses a case
>>
>> and needs more thought. At the VERY least it needs that
>> iov_iter_reexpand() in io_resubmit_prep() too, I think.
>>
>> I'd like the comments expanded too. In particular that
>>
>>                 /* some cases will consume bytes even on error returns */
> 
> That comment is from me, and it goes back a few years. IIRC, it was the
> iomap or xfs code that I hit this with, but honestly I don't remember
> all the details at this point. I can try and play with it and see if it
> still reproduces.

OK, one that I immediately found is just doing O_DIRECT to a block
device or file on XFS. As pages are mapped and added, the iov_iter is
advanced. If we then go and submit and get -EAGAIN, for example, then we
return with what we mapped already consumed.

-- 
Jens Axboe


  reply	other threads:[~2021-09-09 21:39 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 [this message]
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
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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