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 ACC9B366557; Sun, 12 Jul 2026 17:46:23 +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=1783878384; cv=none; b=G6p50wZutVrX++4BAATjeZiNtW8jEMI+zWYSntzS9xM3KYvjxvxZY8WX67/N+cQEfMPnWgLkaZWs6sXnuU09nB6X2QJEBI6c10CAfr2CQhbsosSbYp5sXIM66G9mdFA03Zm8cE6BZm43QvZXdyU0ZJMbSgpUpCbFRrs0XRrxrmI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783878384; c=relaxed/simple; bh=JY71zZN3AcJoRLbQ7PXiopJJONv12qYKHQGDvpxrzvw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=q3SXOg9SYRJyQAxug23I+BtLRDGNDmT565MyoY24c3GttrlH1c0l/KHGamDt5aku9rStq5ZVRmONfz+xsr2NnL7l0A6cppOZFTQAflpZ408FDosUH2WmecIXlMkLJv39x5vcPBKwm+DvZUImA4Zk+W8E0ul8k2qAFoSmsoLgbMg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=js8IV0Pp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="js8IV0Pp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5D421F000E9; Sun, 12 Jul 2026 17:46:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783878383; bh=KHF9t7moUNFfnXNPE/xe3rLfSjmB8jjCrzAU8dZt5Zo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=js8IV0Ppj6bhl38+QsXSYNXuCjtoHIN4n45z8F28u65ZiwZK9blz5bEkRIreaeWS2 fbtG2ZYbQI69WxTizRxtKORWglkuNQJFMvJAg9ffu50QPNS7J2CORVwaHSpFiP4HC4 0YE5bqC1y+91Om4Q4/x52MoRvOeGEzxBJNSQ6pBE77KRHM3o0GI+JLOEGODEVia5FN MLBP8D7EhDzY70MagAnd5iSwbGlacRB74XqQ4w0KBf4PPUIhKxDvS0dgGZBENSRhyd ms/dmcD5+x0JHg0cmKKRdgdwhxQu+1RebmifGXDt3oagLDYCbjVqeMdMY3bkeWNBmN YKVuSSg10K/FA== From: Tejun Heo To: Matt Fleming Cc: David Vernet , Andrea Righi , Changwoo Min , Johannes Weiner , Suren Baghdasaryan , Peter Zijlstra , Edward Adam Davis , Chen Ridong , Zhaoyang Huang , "ziwei . dai" , "ke . wang" , Matt Fleming , sched-ext@lists.linux.dev, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@cloudflare.com, Tejun Heo , Sashiko AI Subject: [PATCH 2/2] sched/psi: Shut down rtpoll_timer in psi_cgroup_free() Date: Sun, 12 Jul 2026 07:46:19 -1000 Message-ID: <20260712174619.3553231-3-tj@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260712174619.3553231-1-tj@kernel.org> References: <20260712174619.3553231-1-tj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit psi_schedule_rtpoll_work() is called locklessly from the scheduler hotpath and can race psi_trigger_destroy() taking down the last rtpoll trigger under rtpoll_trigger_lock: psi_schedule_rtpoll_work() psi_trigger_destroy() rcu_read_lock(); task = rcu_dereference(rtpoll_task); rcu_assign_pointer(rtpoll_task, NULL); timer_delete(&rtpoll_timer); mod_timer(&rtpoll_timer, ...); rcu_read_unlock(); synchronize_rcu(); kthread_stop(task_to_destroy); The group can then be freed with the re-armed timer still pending, and poll_timer_fn() runs on freed memory. 461daba06bdc ("psi: eliminate kthread_worker from psi trigger scheduling mechanism") deleted the timer synchronously after the synchronize_rcu(), which prevented this but raced trigger creation instead: the deletion could cancel the timer that a new trigger set armed during the grace period and, as creation also reinitialized the timer at the time, corrupt it. 8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy") moved the initialization into group_init() and the deletion into the locked section, trading the creation races for the window above. Neither placement in the destruction path works. A pending timer firing while the group is alive is harmless though. poll_timer_fn() just wakes the rtpoll waitqueue and doesn't re-arm itself. Bind the timer to the group's lifetime instead and shut it down in psi_cgroup_free(). Nothing can arm it by then. timer_shutdown_sync() because the timer is never armed again. Fixes: 8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy") Cc: stable@vger.kernel.org # v5.10+ Reported-by: Sashiko AI Closes: https://lore.kernel.org/all/20260711000434.36C4A1F000E9@smtp.kernel.org/ Signed-off-by: Tejun Heo --- kernel/sched/psi.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 565ec7b80743..e2e825dcd088 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -1134,6 +1134,12 @@ void psi_cgroup_free(struct cgroup *cgroup) return; cancel_delayed_work_sync(&cgroup->psi->avgs_work); + /* + * A psi_schedule_rtpoll_work() call racing the last trigger's + * destruction may have re-armed the timer after psi_trigger_destroy() + * deleted it. Spurious firing while the group is alive is harmless. + */ + timer_shutdown_sync(&cgroup->psi->rtpoll_timer); free_percpu(cgroup->psi->pcpu); /* All triggers must be removed by now */ WARN_ONCE(cgroup->psi->rtpoll_states, "psi: trigger leak\n"); -- 2.55.0