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From: Jens Axboe <[email protected]>
To: Xiaoguang Wang <[email protected]>,
	[email protected]
Cc: [email protected], [email protected]
Subject: Re: [PATCH v2] io_uring: fix io_kiocb.flags modification race in IOPOLL mode
Date: Thu, 11 Jun 2020 09:46:17 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 6/11/20 9:39 AM, Xiaoguang Wang wrote:
> While testing io_uring in arm, we found sometimes io_sq_thread() keeps
> polling io requests even though there are not inflight io requests in
> block layer. After some investigations, found a possible race about
> io_kiocb.flags, see below race codes:
>   1) in the end of io_write() or io_read()
>     req->flags &= ~REQ_F_NEED_CLEANUP;
>     kfree(iovec);
>     return ret;
> 
>   2) in io_complete_rw_iopoll()
>     if (res != -EAGAIN)
>         req->flags |= REQ_F_IOPOLL_COMPLETED;
> 
> In IOPOLL mode, io requests still maybe completed by interrupt, then
> above codes are not safe, concurrent modifications to req->flags, which
> is not protected by lock or is not atomic modifications. I also had
> disassemble io_complete_rw_iopoll() in arm:
>    req->flags |= REQ_F_IOPOLL_COMPLETED;
>    0xffff000008387b18 <+76>:    ldr     w0, [x19,#104]
>    0xffff000008387b1c <+80>:    orr     w0, w0, #0x1000
>    0xffff000008387b20 <+84>:    str     w0, [x19,#104]
> 
> Seems that the "req->flags |= REQ_F_IOPOLL_COMPLETED;" is  load and
> modification, two instructions, which obviously is not atomic.
> 
> To fix this issue, add a new iopoll_completed in io_kiocb to indicate
> whether io request is completed.

Looks good, applied, thanks.

-- 
Jens Axboe


      reply	other threads:[~2020-06-11 15:46 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-11 15:39 [PATCH v2] io_uring: fix io_kiocb.flags modification race in IOPOLL mode Xiaoguang Wang
2020-06-11 15:46 ` Jens Axboe [this message]

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