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b=Nc/OMmgden9Sch3xPcq/Wfepqx+lMcRh1nuCXA+s9LMLaVFSV0phw7q8Zj6y7OU4L 2WbojhpIW3mZ0pq2DERzhAdb6SFlujeGUbZGx24FVE9ffsxkrg0fxK/C5JcDQ/OrTx qMwm3hJKuOUCStf87mu11kfTKwRMpjybHFFWwk5UyOIgG6iQozyegxl+kjMXNOji3X zF3MVcCgkuiWZb1Uywq3wpuksX+ImSv3wxCGYrFUPG8iIee4CcyS/79j67gIpttSbV IivPci76szJLZSCEow7zDddBANUG7uNjKY4dIabC/qBHISBY7FgNf2bQfQ1u4VU5Kp YjGIcYnvhWWlg== From: Christian Brauner Date: Mon, 21 Sep 2026 15:44:53 +0200 Subject: [PATCH v3 04/17] 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: <20260921-work-coredump-fixes-v3-4-8e4adb1619e6@kernel.org> References: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> In-Reply-To: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> To: Oleg Nesterov , Chris Mason , linux-fsdevel@vger.kernel.org Cc: Jens Axboe , 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=1786; i=brauner@kernel.org; h=from:subject:message-id; bh=I9adUaO6/vXVSqyRv9Gsx8nEfE1O6rVs+YV8BhcfEiY=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWRtNLkz983aprOS14L4z3Xc9c88/XbC/L3cqw2aPQJTV O06lU+adZSyMIhxMciKKbI4tJuEyy3nqdhslKkBM4eVCWQIAxenAExkxz5GhsnTPmz+ZxKvmcjL lLt6XdO+Fx8jH11xVzxzK4F99V49X2uG/+4ZlRoRKXNOWKYs/KASJ/p9ewEL35H5TDt4ngbfydh 3mh8A X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8F4A5180019 X-Stat-Signature: k4rqzqiuyaca3u94nckefwtatqcxp9za X-Rspam-User: X-HE-Tag: 1789998322-785215 X-HE-Meta: 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 HlF9fz/6 VSSZw3LmkxlbPthUUIOdARjRBBJ3TPMfz4Vt01lbqlU9KxomVBZ1SMT/64wt0UOJQ6MceAsstF9gvLQ0Zu6eJCxtBrbk6pyTqyVq5E4ryBciHXw3fT+Az7MBXAdqX0zfdB2KOBVzGpcNis/HFSfzqnRMmunDVlBPs5fndQauxDWbRmMoZcEGqDR7PkjkJ35uK95XxSi/nJU39IxEuFan/eSPFhXtbMGcvMJ/mFftRb6nVMd5oAVvJxeSHiM9KtGexh8S2ojhwpXz2ngg= 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 Acked-by: Oleg Nesterov 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