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Thu, 24 Sep 2026 15:59:52 -0700 (PDT) Received: from [172.16.11.208] ([4.39.28.114]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3414407d18fsm1457174eec.10.2026.09.24.15.59.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Sep 2026 15:59:52 -0700 (PDT) Message-ID: <096d996d-3028-41ea-bf0c-f7eef1281fcb@kernel.dk> Date: Thu, 24 Sep 2026 16:59:50 -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] io_uring/sqpoll: pin task across task-work publication To: =?UTF-8?B?SsOpcsOpbXkgSmVhbg==?= Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260924205056.3759980-2-Jeremy.Jean@oss.cyber.gouv.fr> Content-Language: en-US From: Jens Axboe In-Reply-To: <20260924205056.3759980-2-Jeremy.Jean@oss.cyber.gouv.fr> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/24/26 2:50 PM, J?r?my Jean wrote: > SQPOLL can consume a request immediately after mpscq_push(). If this > drops the final ring reference, ctx and tctx may be freed before > io_req_normal_work_add() finishes using them. KASAN reports: > > BUG: KASAN: slab-use-after-free in io_req_normal_work_add+0x439/0x510 > Read of size 4 at addr ff11000000ca0000 by task repro/55 > (...) > BUG: KASAN: slab-use-after-free in queue_work_on+0x25/0x70 > Write of size 8 at addr ff11000000c3bd00 by task repro/55 > > Handle SQPOLL before publication. Pin tctx->task, publish the request, > then use only the pinned task so the publication tail cannot dereference > freed contexts. > > Fixes: af5d68f8892f ("io_uring/sqpoll: manage task_work privately") Was going to say this isn't correct, as the mpscq is newer than that. But I suppose this already existed before that, with the previous switch to private task work for SQPOLL? I'll dig into that a bit... > diff --git a/io_uring/tw.c b/io_uring/tw.c > index f573bcc3af6a..2e37a3fd7a33 100644 > --- a/io_uring/tw.c > +++ b/io_uring/tw.c > @@ -210,6 +210,19 @@ void io_req_normal_work_add(struct io_kiocb *req) > struct io_uring_task *tctx = req->tctx; > struct io_ring_ctx *ctx = req->ctx; > > + /* SQPOLL may consume and retire the request immediately after push. */ > + if (ctx->flags & IORING_SETUP_SQPOLL) { > + struct task_struct *task = tctx->task; > + bool first; > + > + get_task_struct(task); > + first = mpscq_push(&tctx->task_list, &req->io_task_work.node); > + if (first) > + __set_notify_signal(task); > + put_task_struct(task); > + return; > + } There's no point in having a 'first' variable. LLM's love bools... if (mpscq_push(&tctx->task_list, &req->io_task_work.node)) __set_notify_signal(task); would be better. -- Jens Axboe