From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5B8592ED850 for ; Tue, 12 Aug 2025 15:22:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755012122; cv=none; b=ex3VI3MsEgvs0Q7SN67F7uP+zesItUCJFPfeWSdjHuEmMlmxDGJ/fIFN62jKYTtTEUUTmvXpJM55eXefN0Y8P+/Cc/rCrLz55+DFInNepmONuW73nRr+XeuXNlw4nMyS8EK+Kaeo8uJmVYV1lkwcH32WPgiYAZUTsxNP5cyhWfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755012122; c=relaxed/simple; bh=3DZsAm/lZ5Laxa8NZLmVrbxw9JmEq/0YL3zuuncOW5g=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=DI7JbPzWm2HJOFNR7+Cx+QPvC7OL9V/HeknkCa/fqejfwciTQxTJwS8aQ3hZXmJ0aM/culoiOuilHKurxeqrfBZKgY1U+JxG0tW6rDopCiFq75KE0yGi8uKLDrqhqzoXdLhCqfNj2CJ5T7ZvCRYRfq5sUnVI/+SZFs766ivvx2Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=O9JjT29L; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="O9JjT29L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 330CDC4CEF0; Tue, 12 Aug 2025 15:22:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1755012121; bh=3DZsAm/lZ5Laxa8NZLmVrbxw9JmEq/0YL3zuuncOW5g=; h=Subject:To:Cc:From:Date:From; b=O9JjT29LekTSD83EiOhNZUoO1urOBeqFTCjzu7Ktxcn4msRW7Iez5iPN20KiIzzWA mZJv6h09qCMbG0SGBV8uRfS3fjMVqyfEUlhaV/ittdAivGF+cNwXfANoy2oBq6BggT DLcOjNePx7cUnz6DXRp9E9Mr8Kk04h8u5I0lcHrM= Subject: FAILED: patch "[PATCH] net: usbnet: Avoid potential RCU stall on LINK_CHANGE event" failed to apply to 5.10-stable tree To: john.ernberg@actia.se,kuba@kernel.org Cc: From: Date: Tue, 12 Aug 2025 17:21:58 +0200 Message-ID: <2025081258-value-bobbing-e1b7@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x 0d9cfc9b8cb17dbc29a98792d36ec39a1cf1395f # git commit -s git send-email --to '' --in-reply-to '2025081258-value-bobbing-e1b7@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 0d9cfc9b8cb17dbc29a98792d36ec39a1cf1395f Mon Sep 17 00:00:00 2001 From: John Ernberg Date: Wed, 23 Jul 2025 10:25:35 +0000 Subject: [PATCH] net: usbnet: Avoid potential RCU stall on LINK_CHANGE event The Gemalto Cinterion PLS83-W modem (cdc_ether) is emitting confusing link up and down events when the WWAN interface is activated on the modem-side. Interrupt URBs will in consecutive polls grab: * Link Connected * Link Disconnected * Link Connected Where the last Connected is then a stable link state. When the system is under load this may cause the unlink_urbs() work in __handle_link_change() to not complete before the next usbnet_link_change() call turns the carrier on again, allowing rx_submit() to queue new SKBs. In that event the URB queue is filled faster than it can drain, ending up in a RCU stall: rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-.... } 33108 jiffies s: 201 root: 0x1/. rcu: blocking rcu_node structures (internal RCU debug): Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 Call trace: arch_local_irq_enable+0x4/0x8 local_bh_enable+0x18/0x20 __netdev_alloc_skb+0x18c/0x1cc rx_submit+0x68/0x1f8 [usbnet] rx_alloc_submit+0x4c/0x74 [usbnet] usbnet_bh+0x1d8/0x218 [usbnet] usbnet_bh_tasklet+0x10/0x18 [usbnet] tasklet_action_common+0xa8/0x110 tasklet_action+0x2c/0x34 handle_softirqs+0x2cc/0x3a0 __do_softirq+0x10/0x18 ____do_softirq+0xc/0x14 call_on_irq_stack+0x24/0x34 do_softirq_own_stack+0x18/0x20 __irq_exit_rcu+0xa8/0xb8 irq_exit_rcu+0xc/0x30 el1_interrupt+0x34/0x48 el1h_64_irq_handler+0x14/0x1c el1h_64_irq+0x68/0x6c _raw_spin_unlock_irqrestore+0x38/0x48 xhci_urb_dequeue+0x1ac/0x45c [xhci_hcd] unlink1+0xd4/0xdc [usbcore] usb_hcd_unlink_urb+0x70/0xb0 [usbcore] usb_unlink_urb+0x24/0x44 [usbcore] unlink_urbs.constprop.0.isra.0+0x64/0xa8 [usbnet] __handle_link_change+0x34/0x70 [usbnet] usbnet_deferred_kevent+0x1c0/0x320 [usbnet] process_scheduled_works+0x2d0/0x48c worker_thread+0x150/0x1dc kthread+0xd8/0xe8 ret_from_fork+0x10/0x20 Get around the problem by delaying the carrier on to the scheduled work. This needs a new flag to keep track of the necessary action. The carrier ok check cannot be removed as it remains required for the LINK_RESET event flow. Fixes: 4b49f58fff00 ("usbnet: handle link change") Cc: stable@vger.kernel.org Signed-off-by: John Ernberg Link: https://patch.msgid.link/20250723102526.1305339-1-john.ernberg@actia.se Signed-off-by: Jakub Kicinski diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index c04e715a4c2a..bc1d8631ffe0 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1122,6 +1122,9 @@ static void __handle_link_change(struct usbnet *dev) * tx queue is stopped by netcore after link becomes off */ } else { + if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags)) + netif_carrier_on(dev->net); + /* submitting URBs for reading packets */ tasklet_schedule(&dev->bh); } @@ -2009,10 +2012,12 @@ EXPORT_SYMBOL(usbnet_manage_power); void usbnet_link_change(struct usbnet *dev, bool link, bool need_reset) { /* update link after link is reseted */ - if (link && !need_reset) - netif_carrier_on(dev->net); - else + if (link && !need_reset) { + set_bit(EVENT_LINK_CARRIER_ON, &dev->flags); + } else { + clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags); netif_carrier_off(dev->net); + } if (need_reset && link) usbnet_defer_kevent(dev, EVENT_LINK_RESET); diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h index 0b9f1e598e3a..4bc6bb01a0eb 100644 --- a/include/linux/usb/usbnet.h +++ b/include/linux/usb/usbnet.h @@ -76,6 +76,7 @@ struct usbnet { # define EVENT_LINK_CHANGE 11 # define EVENT_SET_RX_MODE 12 # define EVENT_NO_IP_ALIGN 13 +# define EVENT_LINK_CARRIER_ON 14 /* This one is special, as it indicates that the device is going away * there are cyclic dependencies between tasklet, timer and bh * that must be broken