Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 1/1] io_uring: fix lockup with timeouts
To:     Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <54e141c75da11f55f607d53c54943b9fee5bbd70.1583532280.git.asml.silence@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <4a96385c-52ea-cba8-455d-6fd3042bd49e@kernel.dk>
Date:   Sat, 7 Mar 2020 08:36:27 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.4.1
MIME-Version: 1.0
In-Reply-To: <54e141c75da11f55f607d53c54943b9fee5bbd70.1583532280.git.asml.silence@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 3/6/20 3:15 PM, Pavel Begunkov wrote:
> There is a recipe to deadlock the kernel: submit a timeout sqe with a
> linked_timeout (e.g.  test_single_link_timeout_ception() from liburing),
> and SIGKILL the process.
> 
> Then, io_kill_timeouts() takes @ctx->completion_lock, but the timeout
> isn't flagged with REQ_F_COMP_LOCKED, and will try to double grab it
> during io_put_free() to cancel the linked timeout. Probably, the same
> can happen with another io_kill_timeout() call site, that is
> io_commit_cqring().

Thanks, looks good, applied.

-- 
Jens Axboe