From eb1e94fee5e27bf2f1dedcf379d566a89715bfcd Mon Sep 17 00:00:00 2001 From: Vishnu Razdan Date: Tue, 25 Aug 2026 09:52:03 -0700 Subject: [PATCH] io_uring/io-wq: fix worker accounting when canceling creation callbacks 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 wq->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 37725c5031b4..a20be1a43aaf 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -193,9 +193,12 @@ static void io_worker_cancel_cb(struct io_worker *worker) struct io_wq *wq = worker->wq; atomic_dec(&acct->nr_running); - raw_spin_lock(&wq->lock); - acct->nr_workers--; - raw_spin_unlock(&wq->lock); + /* create_worker_cb() has not reserved a worker slot yet. */ + if (worker->create_work.func != create_worker_cb) { + raw_spin_lock(&wq->lock); + acct->nr_workers--; + raw_spin_unlock(&wq->lock); + } io_worker_ref_put(wq); clear_bit_unlock(0, &worker->create_state); io_worker_release(worker);