From: Jens Axboe <axboe@kernel.dk>
To: "Stefan Bühler" <source@stbuehler.de>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: io_uring: REQ_F_PREPPED race condition with punting to workers
Date: Fri, 3 May 2019 08:48:16 -0600 [thread overview]
Message-ID: <3900c9a9-41a2-31cb-3a7b-e93251505b15@kernel.dk> (raw)
In-Reply-To: <bdc72cc4-ee7b-db12-baee-47e8f06d30e7@stbuehler.de>
On 5/3/19 4:22 AM, Stefan Bühler wrote:
> Hi,
>
> if the initial operation returns EAGAIN (and REQ_F_NOWAIT) is not set,
> io_submit_sqe copies the SQE for processing in a worker.
>
> The worker will then read from the SQE copy to determine (some)
> parameters for operations, but not all of those parameters will be
> validated again, as the initial operation sets REQ_F_PREPPED.
>
> So between the initial operation and the memcpy is a race in which the
> application could change the SQE: for example it could change from
> IORING_OP_FSYNC to IORING_OP_READV, which would result in broken kiocb
> data afaict.
>
> The only way around that I can see right now is copying the SQE in
> io_submit_sqe (moving the call to io_cqring_add_event to io_submit_sqe
> should simplify this afaict): does that sound acceptable?
I'd be inclined to just fold the prep into the regular handling. The
only prep routine that does any significant work is the read/write one,
and if we're punting to async anyway, it's not a huge hit.
If we do that, then we can get rid of the PREPPED flag and the separate
need to call io_prep_xxx() for the command type.
--
Jens Axboe
next prev parent reply other threads:[~2019-05-03 14:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-03 10:22 io_uring: REQ_F_PREPPED race condition with punting to workers Stefan Bühler
2019-05-03 14:48 ` Jens Axboe [this message]
2019-05-11 17:08 ` [PATCH 1/1] io_uring: fix race condition reading SQE data Stefan Bühler
2019-05-13 15:15 ` Jens Axboe
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