From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C34548A2BC; Mon, 31 Aug 2026 14:03:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788185017; cv=none; b=vGjD7MVqOXaCQbcsS4ldWFeSHNN0lCA4c/TuMhwYOYnr8JFYsf8Uls8mwzBrwbpIJ1LaTGOvoYzDRrgONrDxDb5mlqhVB7mXnmrCWHZ+kfan58zuP/Q2QZg9hUpdABJlQ40QsCtTf7WwgN59A4qFUhqPLLhZbg7sJ3RsuwWdkqc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788185017; c=relaxed/simple; bh=02ThgRFL1a4Tt0QHPldrfM2k9rAixusML87EuSYydxA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HtlZqNZLjus6+BIDyeXc/qdZ3WBK//WvM3kKAslzfBhy6Vl2cuRfc4lOt3YZsQFp2Lag2yKgRkLWgX/DpValBCAz4mcAdNcg0HWtxAR2n/am0u4ae2X2QOFjTszT5bwxeki7B2Ew/s9ZHJZ90mIAwyoQsumA1b9qlrcS71HY23g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=yF7E9kZN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="yF7E9kZN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 774441F000E9; Mon, 31 Aug 2026 14:03:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788185016; bh=VGLAfbTKUy5E7nfn+YQMNFJbTFF0iAXbr0mjdEW9o74=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=yF7E9kZNAQPBcuVOUXi7nh3agdYugs+rbBwUmvhjoA7n4wgY3RTBTjCcOkbaRAICq xC1gwBzuRFGzpn3r2ZhBChPBIbRXPTDii8yJhsN3L9vquiSxshHVTQ5kWW1fKqB0D5 tkPR6D/yRe+kif/9qPhywr+MLhtgWGIQb/iOXzQ8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Gabriel Krisman Bertazi , Vishnu Razdan , Sasha Levin Subject: [PATCH 5.15 03/69] io_uring/io-wq: fix worker accounting when canceling creation callbacks Date: Mon, 31 Aug 2026 15:34:36 +0200 Message-ID: <20260831133358.738879105@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260831133358.601894154@linuxfoundation.org> References: <20260831133358.601894154@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vishnu Razdan commit 297b5ccea4acacaa47c150f043bce695202afbf1 upstream. create_worker_cb() reserves an io-wq worker slot only after its task-work callback runs. If the callback is canceled before then, io_worker_cancel_cb() still decrements acct->nr_workers. When an existing worker retires with its creation callback pending, that worker has already decremented the same account's worker count. The resulting undercount permits worker creation beyond the account's configured limit. On an AST2600 OpenBMC system, an unchanged sensor daemon reached 4,291 threads with the original kernel. With an equivalent downstream fix, 25 passive samples under its normal workload showed 6-9 threads. Decrement nr_workers only when the canceled callback is not create_worker_cb(). Continuation callbacks still release their reserved slot, and both callback types retain the existing running-count, reference-count, and create-state cleanup. [ Backport: retain the existing worker->wqe->lock protecting worker accounting. ] Fixes: 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency") Cc: stable@vger.kernel.org Assisted-by: Codex:gpt-5.6-sol Reviewed-by: Gabriel Krisman Bertazi Link: https://patch.msgid.link/20260811-vrazdan-io-wq-b4-submit-v1-1-719ced16c921@openai.com Signed-off-by: Vishnu Razdan Signed-off-by: Sasha Levin --- io_uring/io-wq.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index edcb5af514b53..f57743d911b4c 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -195,9 +195,12 @@ static void io_worker_cancel_cb(struct io_worker *worker) struct io_wq *wq = wqe->wq; atomic_dec(&acct->nr_running); - raw_spin_lock(&worker->wqe->lock); - acct->nr_workers--; - raw_spin_unlock(&worker->wqe->lock); + /* create_worker_cb() has not reserved a worker slot yet. */ + if (worker->create_work.func != create_worker_cb) { + raw_spin_lock(&worker->wqe->lock); + acct->nr_workers--; + raw_spin_unlock(&worker->wqe->lock); + } io_worker_ref_put(wq); clear_bit_unlock(0, &worker->create_state); io_worker_release(worker); -- 2.53.0