IO-Uring Archive on lore.kernel.org
 help / color / Atom feed
From: Pavel Begunkov <asml.silence@gmail.com>
To: Dmitrii Dolgov <9erthalion6@gmail.com>,
	axboe@kernel.dk, io-uring@vger.kernel.org
Subject: Re: [RFC] Check if file_data is initialized
Date: Thu, 9 Jan 2020 17:26:15 +0300
Message-ID: <e6cd2afe-565f-8cde-652c-26c52b888962@gmail.com> (raw)
In-Reply-To: <20200109131750.30468-1-9erthalion6@gmail.com>

On 1/9/2020 4:17 PM, Dmitrii Dolgov wrote:
> With combination of --fixedbufs and an old version of fio I've managed
> to get a strange situation, when doing io_iopoll_complete NULL pointer
> dereference on file_data was caused in io_free_req_many. Interesting
> enough, the very same configuration doesn't fail on a newest version of
> fio (the old one is fc220349e4514, the new one is 2198a6b5a9f4), but I
> guess it still makes sense to have this check if it's possible to craft
> such request to io_uring.

I didn't looked up why it could become NULL in the first place, but the
problem is probably deeper.

1. I don't see why it puts @rb->to_free @file_data->refs, even though
there could be non-fixed reqs. It needs to count REQ_F_FIXED_FILE reqs
and put only as much.

2. Jens, there is another line bothering me, could you take a look?

io_free_req_many()
{
...
	if (req->flags & REQ_F_INFLIGHT) ...;
	else
		rb->reqs[i] = NULL;
...
}

It zeroes rb->reqs[i], calls __io_req_aux_free(), but did not free
memory for the request itself. Is it as intended?

> 
> More details about configuration:
> 
> [global]
> filename=/dev/vda
> rw=randread
> bs=256k
> direct=1
> time_based=1
> randrepeat=1
> gtod_reduce=1
> 
> [fiotest]
> 
> fio test.fio \
>     --readonly \
>     --ioengine=io_uring \
>     --iodepth 1024 \
>     --fixedbufs \
>     --hipri \
>     --numjobs=1 \
>     --runtime=10
> 
> Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
> ---
>  fs/io_uring.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> I'm not entirely sure if my analysis is correct, but since this change
> fixes the issue for me, I've decided to post it.
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c770c2c0eb52..c5e69dfc0221 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1232,7 +1232,8 @@ static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
>  do_free:
>  	kmem_cache_free_bulk(req_cachep, rb->to_free, rb->reqs);
>  	percpu_ref_put_many(&ctx->refs, rb->to_free);
> -	percpu_ref_put_many(&ctx->file_data->refs, rb->to_free);
> +	if (ctx->file_data)
> +		percpu_ref_put_many(&ctx->file_data->refs, rb->to_free);
>  	rb->to_free = rb->need_iter = 0;
>  }
>  
> 

-- 
Pavel Begunkov

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-09 13:17 Dmitrii Dolgov
2020-01-09 14:26 ` Pavel Begunkov [this message]
2020-01-09 14:51   ` Jens Axboe
2020-01-09 15:17     ` Pavel Begunkov
2020-01-09 15:23       ` Jens Axboe
2020-01-09 15:32         ` Pavel Begunkov
2020-01-09 15:34       ` Jens Axboe
2020-01-09 16:04     ` Dmitry Dolgov
2020-01-09 16:19       ` Jens Axboe
2020-01-09 14:45 ` Jens Axboe

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=e6cd2afe-565f-8cde-652c-26c52b888962@gmail.com \
    --to=asml.silence@gmail.com \
    --cc=9erthalion6@gmail.com \
    --cc=axboe@kernel.dk \
    --cc=io-uring@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IO-Uring Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/io-uring/0 io-uring/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 io-uring io-uring/ https://lore.kernel.org/io-uring \
		io-uring@vger.kernel.org
	public-inbox-index io-uring

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.io-uring


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git