From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oo1-f69.google.com (mail-oo1-f69.google.com [209.85.161.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2708A40DFCC for ; Sun, 5 Apr 2026 05:18:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775366283; cv=none; b=sQ0qcJZ3zgzF+JIDCLA37MWks/22Fn0DuK2mqsit3iYghN2owoGQxq4ieb3InZJdkdZpgGih+TjV81HONCeHwZQjkC6bQ30t+T6Q+Gv8dQBRGNfoZEcqSs+P7VAhl97AtsiDQcPIazgTkSdKstjHq2GB4u8LBSPptZb0v9GZ5GA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775366283; c=relaxed/simple; bh=l2omWhsRFdSUZp6LdhFg699Q1ftwhCvss6JUUPKbHuw=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=QqLE1jeh9GAvnJ4G2W0o2qsD2RKQl9HQCfurUoTu1j7ZmmaLR7AIdqLCrh1i+JORIgZaFX/kTa3sNiFfbfdOBKR3hLeYuCNrgLAY2iJ25U4S3zYNmWp4ULN1DgqitlOaAGZEzj1UyJ4sy+opY6pA+kPKsRMLyslzh2J0NIjC8rU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f69.google.com with SMTP id 006d021491bc7-682644bbbb5so3637051eaf.2 for ; Sat, 04 Apr 2026 22:18:01 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775366281; x=1775971081; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=7qSq8lkChLq7Yzb4xWV41+00IX38ukPWXteq05rT3LE=; b=GKM6N8Z0qULt7qnSjEGdYjQvLN4M4dMCyOPMxfbMZdWNchhnSHholiTlteYJf71lLB O/kQ1f9/nc2zmut/QaFPEI/CayXR/w88RVjSbxnU38NGe/Y53/e+a7kt9Z83aAk8L1Fr /zban3BuTusnIE9IhhKGF+UkhLE+wWhl1DmdhBxHYQDFZPDRLRd+ZbxKh3VQzSnJbGvp z0fgKt456CCO7UzOEovv3yTxMDBCnZ8Uw5qKdt6MXN8l5avmXO10MTI6vXbThHCdx3Ho +d/9SUpT1dy3EZYEZdvVLg1PF66oKGCAqhC1iqqXSuzDFN15zCxdjtnbQdpuCcqxB3eA Hheg== X-Gm-Message-State: AOJu0Yzoh1AIweqHBUAGwEcru2PUhGJKcDL53sBpcVNpHHI3QQdF2z67 2zpRkEWXUchOdCzZaK8hpWezZn1MJps/Ew4KTCOgYB6mq4i2lqJ16EyxfsAQmQQeNm5hGuQYIN4 SGC0WczeerbebfO3AaRvVYtl1iffuOgFN2I2cYDuaWqaEtfcZCHoqCNd8Rck= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a4a:ee0f:0:b0:681:b070:3dc6 with SMTP id 006d021491bc7-6821d23ec2cmr4489942eaf.10.1775366281071; Sat, 04 Apr 2026 22:18:01 -0700 (PDT) Date: Sat, 04 Apr 2026 22:18:01 -0700 In-Reply-To: <69cffde1.050a0220.182279.0016.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69d1f089.a70a0220.a26f2.001d.GAE@google.com> Subject: Forwarded: [PATCH] ath9k: defer reg_in URB resubmission to workqueue to fix RCU stall From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] ath9k: defer reg_in URB resubmission to workqueue to fix RCU stall Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master ath9k_hif_usb_reg_in_cb() is a URB completion callback that runs in softirq context via dummy_hcd's hrtimer which is registered with HRTIMER_MODE_REL_SOFT. Calling usb_submit_urb() directly from this softirq context triggers a long synchronous chain: dummy_urb_enqueue() hrtimer_start(HRTIMER_MODE_REL_SOFT) dummy_timer() __usb_hcd_giveback_urb() ath9k_hif_usb_reg_in_cb() usb_submit_urb() <- back to start This keeps the CPU busy in softirq context indefinitely, starving the rcu_preempt kthread and causing an RCU stall: rcu: rcu_preempt kthread starved for 3053 jiffies! rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. Fix this by introducing a small per-resubmission wrapper struct (reg_in_work) that is freshly allocated on each URB completion and carries its own work_struct. The resubmission is deferred to a dedicated ordered workqueue (reg_in_wq) via queue_work(), allowing the softirq to exit quickly. Using a fresh wrapper per completion avoids races that would arise from reusing a single embedded work_struct: - INIT_WORK() is called on a newly allocated struct so there is no risk of reinitialising a work item that is still queued or running. - queue_work() on a fresh work_struct always succeeds so no resubmission is ever silently dropped. - usb_get_urb() is called before queue_work() and usb_put_urb() is called last in the worker after all URB accesses are complete, ensuring the URB remains valid for the entire lifetime of the work item. A dedicated ordered workqueue is used instead of the system workqueue to allow proper synchronization on disconnect. destroy_workqueue() in ath9k_hif_usb_dealloc_reg_in_urbs() drains all pending resubmissions before hif_dev is freed, preventing use-after-free when the device is disconnected while work items are still pending. On resubmission failure in the worker the original error path is preserved: skb and rx_buf are freed and urb->context is set to NULL before dropping the URB reference, matching the behaviour of the original goto free_skb path. Reported-by: syzbot+9b95da55ba5146a60734@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?extid=9b95da55ba5146a60734 Signed-off-by: Deepanshu Kartikey --- drivers/net/wireless/ath/ath9k/hif_usb.c | 58 ++++++++++++++++++++---- drivers/net/wireless/ath/ath9k/hif_usb.h | 1 + 2 files changed, 51 insertions(+), 8 deletions(-) diff --git a/drivers/net/wireless/ath/ath9k/hif_usb.c b/drivers/net/wireless/ath/ath9k/hif_usb.c index 8533b88974b2..370764681749 100644 --- a/drivers/net/wireless/ath/ath9k/hif_usb.c +++ b/drivers/net/wireless/ath/ath9k/hif_usb.c @@ -731,12 +731,43 @@ static void ath9k_hif_usb_rx_cb(struct urb *urb) kfree(rx_buf); } +struct reg_in_work { + struct urb *urb; + struct hif_device_usb *hif_dev; + struct work_struct work; +}; + +static void ath9k_hif_usb_reg_in_resubmit(struct work_struct *work) +{ + struct reg_in_work *rw = container_of(work, + struct reg_in_work, + work); + struct urb *urb = rw->urb; + struct rx_buf *rx_buf = urb->context; + + int ret; + + usb_anchor_urb(rw->urb, &rw->hif_dev->reg_in_submitted); + ret = usb_submit_urb(rw->urb, GFP_KERNEL); + + if (ret) { + usb_unanchor_urb(rw->urb); + if (rx_buf) { + kfree_skb(rx_buf->skb); + kfree(rx_buf); + urb->context = NULL; + } + } + + usb_put_urb(urb); + kfree(rw); +} + static void ath9k_hif_usb_reg_in_cb(struct urb *urb) { struct rx_buf *rx_buf = urb->context; struct hif_device_usb *hif_dev = rx_buf->hif_dev; struct sk_buff *skb = rx_buf->skb; - int ret; if (!skb) return; @@ -786,14 +817,20 @@ static void ath9k_hif_usb_reg_in_cb(struct urb *urb) } resubmit: - usb_anchor_urb(urb, &hif_dev->reg_in_submitted); - ret = usb_submit_urb(urb, GFP_ATOMIC); - if (ret) { - usb_unanchor_urb(urb); - goto free_skb; + { + struct reg_in_work *rw; + + rw = kmalloc_obj(*rw, GFP_ATOMIC); + if (!rw) + goto free_skb; + + rw->urb = urb; + rw->hif_dev = hif_dev; + usb_get_urb(urb); + INIT_WORK(&rw->work, ath9k_hif_usb_reg_in_resubmit); + queue_work(hif_dev->reg_in_wq, &rw->work); + return; } - - return; free_skb: kfree_skb(skb); free_rx_buf: @@ -959,6 +996,8 @@ static int ath9k_hif_usb_alloc_rx_urbs(struct hif_device_usb *hif_dev) static void ath9k_hif_usb_dealloc_reg_in_urbs(struct hif_device_usb *hif_dev) { usb_kill_anchored_urbs(&hif_dev->reg_in_submitted); + if (hif_dev->reg_in_wq) + destroy_workqueue(hif_dev->reg_in_wq); } static int ath9k_hif_usb_alloc_reg_in_urbs(struct hif_device_usb *hif_dev) @@ -969,6 +1008,9 @@ static int ath9k_hif_usb_alloc_reg_in_urbs(struct hif_device_usb *hif_dev) int i, ret; init_usb_anchor(&hif_dev->reg_in_submitted); + hif_dev->reg_in_wq = alloc_ordered_workqueue("ath9k_reg_in", 0); + if (!hif_dev->reg_in_wq) + return -ENOMEM; for (i = 0; i < MAX_REG_IN_URB_NUM; i++) { diff --git a/drivers/net/wireless/ath/ath9k/hif_usb.h b/drivers/net/wireless/ath/ath9k/hif_usb.h index b3e66b0485a5..38f17a12fd5f 100644 --- a/drivers/net/wireless/ath/ath9k/hif_usb.h +++ b/drivers/net/wireless/ath/ath9k/hif_usb.h @@ -124,6 +124,7 @@ struct hif_device_usb { struct usb_anchor regout_submitted; struct usb_anchor rx_submitted; struct usb_anchor reg_in_submitted; + struct workqueue_struct *reg_in_wq; struct usb_anchor mgmt_submitted; struct sk_buff *remain_skb; char fw_name[64]; -- 2.43.0