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b=QtWatflMw9JiFnRUXdSAc7swvK4m4NId/J7Z624S4xfFaNesuZMGlGsXtHYU2w4+s rYlZlMcCrn7JUPaTQrDVdNgVyzlhMzi3J+g22RarfHlFPwpiMTHl0tT2B7HOJ0ag0W Ks0Cz7FzJwV6cSTEpsWIuzkvfKJpKWoT0+jslfXUfe9P6SB+oEoEFFsTt19Pmcofqh OZKkoB9KWaZ1jUUXlYNPDy4L6EozDmVfI+KCZE8BCUDKRJBjWNuwnde+XppfBqrdx6 qFItvM2FBlBxHHyzlSpTmRszC3RvBm8UIb1JitSeh0WiccX1N2H6EmDRrwrmU9RTlU MXcf8yyfIDgNw== From: Christian Brauner Date: Thu, 17 Sep 2026 11:17:32 +0200 Subject: [PATCH v2 5/7] io-wq: order the exit bit against worker creation task work MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260917-work-coredump-fixes-v2-5-f3787fcda051@kernel.org> References: <20260917-work-coredump-fixes-v2-0-f3787fcda051@kernel.org> In-Reply-To: <20260917-work-coredump-fixes-v2-0-f3787fcda051@kernel.org> To: Oleg Nesterov , Jens Axboe , linux-fsdevel@vger.kernel.org Cc: Alexander Viro , Jan Kara , NeilBrown , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org, io-uring@vger.kernel.org, "Christian Brauner (Amutable)" , stable@vger.kernel.org X-Mailer: b4 0.17-dev-db0b7 X-Developer-Signature: v=1; a=openpgp-sha256; l=1743; i=brauner@kernel.org; h=from:subject:message-id; bh=te/fE1/4OvwEnuyl6ZC8l75gKxQO4sF0WSk/gVTYDMg=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWSt3mDy36CneMHryFdy5z1fKNrdVJl99bXqkuaK/lKml SxbH6U/7ihlYRDjYpAVU2RxaDcJl1vOU7HZKFMDZg4rE8gQBi5OAZiIVQTD/1K++zll+1wELhcX 1NXdKa+WKOjdvmHbsR6H+JdTF/6on8/I0LxY6FLR3SMWT1K3FhksVGD89EgnPilY9+8RN5ecBxv NuAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0BE572000A X-Stat-Signature: jxxig47mo85af7tdhsikhbxtoa5x6e8k X-Rspam-User: X-HE-Tag: 1789636682-643207 X-HE-Meta: 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 Uaw+ae4D SBg11DnikiQ8fuojpk9aPvyTgMFIyUFVFKC3c+FxuBizDtdM8r6B3sVqn2UI5GdzbgIR7b1Nvur2tif06ssblCCmYZG5dftLA3KZuqYP9rckXBBntYsDhgFCncvugU/TRTSaiXAKxy372LTsX1ZfNLQRLu5QTIvT8Lm/wqhejWV8OMVaBTdNG3N1edSdrFpszeU+CZn3wPVhubqxIJZm23a3hxRdi/Tfa0NXE3LJcINOCVfVAqHf5bN7ozg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: io_wq_exit_workers() cancels task work for queued worker creation with task_work_cancel_match(). That has a plain load of task->task_works. io_queue_worker_create() adds the new entry and tests IO_WQ_BIT_EXIT to cancel it if the workqueue is already on its way out. That must be ordered. task_work_add() has a full barrier via cmpxchg(). But io_wq_exit_start() sets the bit with set_bit() which doesn't have any memory ordering. So afaict, on weakly ordered architectures the exiting task may load task_works before the store of the bit is visible. The other side tests the bit before the store is visible as well. So the entry remains queued with worker_refs and the exiting task waits on worker_done indefinitely. If the task still has rings then io_uring_del_tctx_node() provides the barrier via test_and_set_bit() in io_wq_set_exit_on_idle(). When it has closed all rings though that barrier is gone. Add the barrier after the set_bit(). Fixes: 71a85387546e ("io-wq: check for wq exit after adding new worker task_work") Cc: stable@vger.kernel.org Reviewed-by: Jens Axboe Signed-off-by: Christian Brauner (Amutable) --- io_uring/io-wq.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index 2ca223e47d41..2a980e86dd94 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -1324,6 +1324,8 @@ static bool io_task_work_match(struct callback_head *cb, void *data) void io_wq_exit_start(struct io_wq *wq) { set_bit(IO_WQ_BIT_EXIT, &wq->state); + /* Pairs with task_work_add() in io_queue_worker_create(). */ + smp_mb__after_atomic(); } static void io_wq_cancel_tw_create(struct io_wq *wq) -- 2.53.0