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Thu, 16 Apr 2026 08:28:36 -0700 (PDT) Message-ID: Date: Thu, 16 Apr 2026 09:28:34 -0600 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] io_uring/poll: fix signed comparison in io_poll_get_ownership() To: Yuan Tan , Ren Wei , io-uring@vger.kernel.org Cc: asml.silence@gmail.com, yifanwucs@gmail.com, tomapufckgml@gmail.com, bird@lzu.edu.cn, zcliangcn@gmail.com, ylong030@ucr.edu References: <3a3508b08bcd7f1bc3beff848ae6e1d73d355043.1775965597.git.ylong030@ucr.edu> <6dc4f9dd-975b-436f-889b-7c584bc18e62@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/15/26 7:50 PM, Yuan Tan wrote: > > On 4/15/26 13:09, Jens Axboe wrote: >> On 4/12/26 2:38 AM, Ren Wei wrote: >>> From: Longxuan Yu >>> >>> io_poll_get_ownership() uses a signed comparison to check whether >>> poll_refs has reached the threshold for the slowpath: >>> >>> if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS)) >>> >>> atomic_read() returns int (signed). When IO_POLL_CANCEL_FLAG >>> (BIT(31)) is set in poll_refs, the value becomes negative in >>> signed arithmetic, so the >= 128 comparison always evaluates to >>> false and the slowpath is never taken. >>> >>> Fix this by casting the atomic_read() result to unsigned int >>> before the comparison, so that the cancel flag is treated as a >>> large positive value and correctly triggers the slowpath. >>> >>> Fixes: aa43477b0402 ("io_uring: poll rework") >> Is this correct? Seems it should be: >> >> Fixes: a26a35e9019f ("io_uring: make poll refs more robust") >> > I just double check it. Yes we were wrong. Correct bug inducing commit is  > > a26a35e9019f ("io_uring: make poll refs more robust"). > > Thanks for pointing it out. > > > Do we need to send a v2 to fix this? No need, I corrected it already while applying yesterday. -- Jens Axboe