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Fri, 01 May 2026 04:05:28 -0700 (PDT) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7ded51a9612sm839214a34.26.2026.05.01.04.05.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 May 2026 04:05:27 -0700 (PDT) Message-ID: Date: Fri, 1 May 2026 05:05:26 -0600 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] ublk: reject FETCH from non-userspace context To: Ming Lei Cc: linux-block@vger.kernel.org, Caleb Sander Mateos , Uday Shankar References: <20260501085216.905401-1-tom.leiming@gmail.com> <9efbd035-b40e-4155-8382-b42acff75a9e@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/1/26 4:54 AM, Ming Lei wrote: > On Fri, May 01, 2026 at 04:38:22AM -0600, Jens Axboe wrote: >> On 5/1/26 4:36 AM, Ming Lei wrote: >>> On Fri, May 01, 2026 at 04:34:11AM -0600, Jens Axboe wrote: >>>> On 5/1/26 2:52 AM, Ming Lei wrote: >>>>> __ublk_fetch() sets io->task to current, which is later checked >>>>> against io_uring_cmd_get_task() in ublk_uring_cmd_cancel_fn(). >>>>> With REQ_F_FORCE_ASYNC, the FETCH uring_cmd can be issued from >>>>> task work, which can be run from io_uring's fallback workqueue, >>>>> causing a task mismatch and triggering the WARN in cancel_fn. >>>>> >>>>> Reject FETCH if current is not a real userspace task, and it is >>>>> reasonable for failing it in case of io_uring fallback. >>>> >>>> I think this should be caught in ublk_ch_uring_cmd_cb(), which >>>> should not hit ublk_ch_uring_cmd_local() if tw.cancel is true. >>>> fallback work should just be terminated, not be issued. >>> >>> Yeah, that is definitely better, will take it in V2. >> >> Something like this, totally untested. Caveat: probably worth checking >> the other tw paths in ublk as well! > > tw.cancel can replace the check in ublk_dispatch_req() for ublk_cmd_tw_cb() and > ublk_cmd_list_tw_cb(), which is one cleanup. > > ublk_batch_tw_cb() doesn't track io task, so it is just fine. Sounds good to me. >> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c >> index 8e5f3738c203..d10460d29e4a 100644 >> --- a/drivers/block/ublk_drv.c >> +++ b/drivers/block/ublk_drv.c >> @@ -3496,8 +3496,10 @@ static void ublk_ch_uring_cmd_cb(struct io_tw_req tw_req, io_tw_token_t tw) >> { >> unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS; >> struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req); >> - int ret = ublk_ch_uring_cmd_local(cmd, issue_flags); >> + int ret = -ECANCELED; >> >> + if (!tw.cancel) >> + ret = ublk_ch_uring_cmd_local(cmd, issue_flags); >> if (ret != -EIOCBQUEUED) >> io_uring_cmd_done(cmd, ret, issue_flags); >> } > > This fix looks good. Feel free to just run with it or make it part of a fixup series. -- Jens Axboe