From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 B0F3D360EEE for ; Thu, 23 Jul 2026 10:05:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784801148; cv=none; b=G1rvWFKhYaudINLLi2Tb7eVXxa3wMF4B1euihqY1zF7NvIiOH0nbus1+pwunU4CXq2yBnPpHzifnvrkcm84eftMGt6Gm56lflaR+ubXxKSdEcv1NOtyjvt3NfQy4RymrWcvay7DC8PPmBzKJ0fGHyoOu5s6a2lB3t3LWJz+FhDc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784801148; c=relaxed/simple; bh=cGglKTVxub8fpqSlz6JJI47B+oqgmdmim1g0fVnb5Dg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DVcM+0TA2t7ahdEyI5a/EIyKYVtwNKOTSMYr7vjcD1Ezcos06Am8ucZc25CHdsPR6EHVcE5p43X3FdJBCCcwzEuFkNkqkZhy9G9Sp+rp5+e1p0t27OzFOFlQV+N6YowzBbY1k8rKcwl+SBsOwKFlV1hJ4onP8tUeqxgwd295fAE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=qfYfG9cO; arc=none smtp.client-ip=91.218.175.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="qfYfG9cO" Message-ID: <7ced0697-e968-4e4f-b529-e333eae764f9@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784801142; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/ADYPGwARCkWXKejUcBpoZqxXd5DnABnAkLDFbqIshw=; b=qfYfG9cOu4lz4rB96rwO9oBKCsH/GEfSQCUeXHNEKWBy5s/OaU5pwdjGFZZ2xHzzXdNX2C uyBNJ+n6bO/XO+3HioRyX6EIe8gwcQWTYGpg9dIT4UQtHWvsYiH3qWjTIKN2z8F3T9Tagw izWgLDuBuJ1qPKIdjyaIpLcMEIAT7/I= Date: Thu, 23 Jul 2026 11:05:38 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH can v3] can: gs_usb: fix hardware timestamp state for mixed channels To: Shuangpeng Cc: mkl@pengutronix.de, mailhol@kernel.org, uwu@coelacanthus.name, kees@kernel.org, linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260720184042.1712217-1-shuangpeng.kernel@gmail.com> <97232020-922B-42BE-B050-A42B6FF40B85@gmail.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Vadim Fedorenko In-Reply-To: <97232020-922B-42BE-B050-A42B6FF40B85@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 23/07/2026 06:17, Shuangpeng wrote: > > >> On Jul 20, 2026, at 18:35, Vadim Fedorenko wrote: >> >> On 20.07.2026 19:40, Shuangpeng Bai wrote: >>> The hardware timestamp state is shared by struct gs_usb, but >>> gs_can_open() and gs_can_close() tie its initialization and teardown to >>> active_channels and to the feature bits of the channel being opened or >>> closed. >>> This is wrong for mixed-channel devices in both directions. If a >>> non-timestamp channel opens first, a later timestamp-capable channel does >>> not initialize the shared cyclecounter/timecounter because active_channels >>> is already non-zero. Timestamp RX then calls timecounter_cyc2time() with >>> parent->tc.cc unset. >>> Conversely, if a timestamp-capable channel opens first and starts the >>> shared delayed work, then closes while a non-timestamp channel remains >>> active, disconnect may close the non-timestamp channel last. The old >>> teardown check skips gs_usb_timestamp_stop() in that case and frees >>> struct gs_usb while the delayed work timer is still queued. >>> Count the number of active timestamp-capable channels instead. Start the >>> shared timestamp state when the first such channel opens, stop it when the >>> last such channel closes, and unwind the count if open fails. >>> Initialize the shared timestamp lock and delayed work once during probe. >>> The first timestamp-capable channel may be opened while RX URBs are >>> already active, so guard the count and timecounter access with the same >>> lock. Keep the count zero until timecounter_init() completes, and make RX >>> and delayed work skip the timecounter while the count is zero. >>> Fixes: 45dfa45f52e6 ("can: gs_usb: add RX and TX hardware timestamp support") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Shuangpeng Bai >>> --- >>> Changes in v3: >>> - Drop Suggested-by tag. >>> - Move active_timestamp_channels management into the timestamp init/stop >>> helpers. >>> - Protect active_timestamp_channels with tc_lock, and keep it zero until >>> timecounter_init() has completed. >>> - Make RX timestamp conversion and the delayed work skip the timecounter >>> while no timestamp-capable channel is active. >>> - Initialize the shared timestamp lock and delayed work once during probe. >>> Changes in v2: >>> - Count active timestamp-capable channels instead of tracking only whether >>> the shared timestamp worker has been started. >>> - Stop the shared timestamp worker when the last timestamp-capable channel >>> closes, even if non-timestamp channels remain open. >>> - Unwind the timestamp-capable channel count on gs_can_open() failures. >>> drivers/net/can/usb/gs_usb.c | 81 ++++++++++++++++++++++++------------ >>> 1 file changed, 54 insertions(+), 27 deletions(-) >>> diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c >>> index ec9a7cbbbc69..be25d82cedcb 100644 >>> --- a/drivers/net/can/usb/gs_usb.c >>> +++ b/drivers/net/can/usb/gs_usb.c >>> @@ -337,6 +337,7 @@ struct gs_usb { >>> unsigned int hf_size_rx; >>> u8 active_channels; >>> + u8 active_timestamp_channels; >>> u8 channel_cnt; >>> unsigned int pipe_in; >>> @@ -447,14 +448,20 @@ static void gs_usb_timestamp_work(struct work_struct *work) >>> { >>> struct delayed_work *delayed_work = to_delayed_work(work); >>> struct gs_usb *parent; >>> + bool active; >>> parent = container_of(delayed_work, struct gs_usb, timestamp); >>> spin_lock_bh(&parent->tc_lock); >>> - timecounter_read(&parent->tc); >>> + active = parent->active_timestamp_channels; >>> + if (active) { >>> + timecounter_read(&parent->tc); >>> + active = parent->active_timestamp_channels; >>> + } >>> spin_unlock_bh(&parent->tc_lock); >>> - schedule_delayed_work(&parent->timestamp, >>> - GS_USB_TIMESTAMP_WORK_DELAY_SEC * HZ); >>> + if (active) >>> + schedule_delayed_work(&parent->timestamp, >>> + GS_USB_TIMESTAMP_WORK_DELAY_SEC * HZ); >>> } >>> static void gs_usb_skb_set_timestamp(struct gs_can *dev, >>> @@ -465,6 +472,11 @@ static void gs_usb_skb_set_timestamp(struct gs_can *dev, >>> u64 ns; >>> spin_lock_bh(&parent->tc_lock); >>> + if (!parent->active_timestamp_channels) { >>> + spin_unlock_bh(&parent->tc_lock); >>> + return; >>> + } >>> + >>> ns = timecounter_cyc2time(&parent->tc, timestamp); >>> spin_unlock_bh(&parent->tc_lock); >>> @@ -474,25 +486,40 @@ static void gs_usb_skb_set_timestamp(struct gs_can *dev, >>> static void gs_usb_timestamp_init(struct gs_usb *parent) >>> { >>> struct cyclecounter *cc = &parent->cc; >>> + bool first = false; >>> - cc->read = gs_usb_timestamp_read; >>> - cc->mask = CYCLECOUNTER_MASK(32); >>> - cc->shift = 32 - bits_per(NSEC_PER_SEC / GS_USB_TIMESTAMP_TIMER_HZ); >>> - cc->mult = clocksource_hz2mult(GS_USB_TIMESTAMP_TIMER_HZ, cc->shift); >>> - >>> - spin_lock_init(&parent->tc_lock); >>> spin_lock_bh(&parent->tc_lock); >>> - timecounter_init(&parent->tc, &parent->cc, ktime_get_real_ns()); >>> + if (!parent->active_timestamp_channels) { >>> + cc->read = gs_usb_timestamp_read; >>> + cc->mask = CYCLECOUNTER_MASK(32); >>> + cc->shift = 32 - bits_per(NSEC_PER_SEC / >>> + GS_USB_TIMESTAMP_TIMER_HZ); >>> + cc->mult = clocksource_hz2mult(GS_USB_TIMESTAMP_TIMER_HZ, >>> + cc->shift); >>> + >>> + timecounter_init(&parent->tc, &parent->cc, >>> + ktime_get_real_ns()); >>> + first = true; >>> + } >>> + parent->active_timestamp_channels++; >>> spin_unlock_bh(&parent->tc_lock); >>> - INIT_DELAYED_WORK(&parent->timestamp, gs_usb_timestamp_work); >>> - schedule_delayed_work(&parent->timestamp, >>> - GS_USB_TIMESTAMP_WORK_DELAY_SEC * HZ); >>> + if (first) >>> + schedule_delayed_work(&parent->timestamp, >>> + GS_USB_TIMESTAMP_WORK_DELAY_SEC * HZ); >>> } >>> static void gs_usb_timestamp_stop(struct gs_usb *parent) >>> { >>> - cancel_delayed_work_sync(&parent->timestamp); >>> + bool last; >>> + >>> + spin_lock_bh(&parent->tc_lock); >>> + parent->active_timestamp_channels--; >>> + last = !parent->active_timestamp_channels; >>> + spin_unlock_bh(&parent->tc_lock); >>> + >>> + if (last) >>> + cancel_delayed_work_sync(&parent->timestamp); >>> } >>> >> >> tc_lock serializes active_timestamp_channels updates, but this work manipulation >> is not protected. Imagine CPU0 doing gs_usb_timestamp_stop while CPU1 is doing >> gs_can_open: >> >> CPU0 CPU1 >> >> gs_usb_timestamp_stop() gs_usb_timestamp_init() >> spin_lock_bh(&tc_lock); >> active_timestamp_channels-- >> last = true >> spin_unlock_bh(&tc_lock); >> ... spin_lock_bh(&tc_lock) >> ... timecounter_init() >> ... first = true; >> ... spin_unlock_bh(&tc_lock) >> ... schedule_delayed_work() >> cancel_delayed_work_sync() >> >> And the device will have no worker while active_timestamp_channels is not 0. >> >> I think we have to find another way of synchronization here. >> > > Thanks for your check. > > I thought these paths were already serialized by RTNL through > ndo_open/ndo_stop. If additional synchronization is needed, > do you have any suggestions? Ok, fair, but we are slowly moving towards per-device locks. May need to revisit this part later. Reviewed-by: Vadim Fedorenko > >> >>> static void gs_update_state(struct gs_can *dev, struct can_frame *cf) >>> @@ -980,10 +1007,10 @@ static int gs_can_open(struct net_device *netdev) >>> can_rx_offload_enable(&dev->offload); >>> - if (!parent->active_channels) { >>> - if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> - gs_usb_timestamp_init(parent); >>> + if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> + gs_usb_timestamp_init(parent); >>> + if (!parent->active_channels) { >>> for (i = 0; i < GS_MAX_RX_URBS; i++) { >>> u8 *buf; >>> @@ -1094,12 +1121,11 @@ static int gs_can_open(struct net_device *netdev) >>> out_usb_free_urb: >>> usb_free_urb(urb); >>> out_usb_kill_anchored_urbs: >>> - if (!parent->active_channels) { >>> - usb_kill_anchored_urbs(&parent->rx_submitted); >>> + if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> + gs_usb_timestamp_stop(parent); >>> - if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> - gs_usb_timestamp_stop(parent); >>> - } >>> + if (!parent->active_channels) >>> + usb_kill_anchored_urbs(&parent->rx_submitted); >>> can_rx_offload_disable(&dev->offload); >>> close_candev(netdev); >>> @@ -1152,12 +1178,11 @@ static int gs_can_close(struct net_device *netdev) >>> /* Stop polling */ >>> parent->active_channels--; >>> - if (!parent->active_channels) { >>> - usb_kill_anchored_urbs(&parent->rx_submitted); >>> + if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> + gs_usb_timestamp_stop(parent); >>> - if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP) >>> - gs_usb_timestamp_stop(parent); >>> - } >>> + if (!parent->active_channels) >>> + usb_kill_anchored_urbs(&parent->rx_submitted); >>> /* Stop sending URBs */ >>> usb_kill_anchored_urbs(&dev->tx_submitted); >>> @@ -1577,6 +1602,8 @@ static int gs_usb_probe(struct usb_interface *intf, >>> parent->channel_cnt = icount; >>> init_usb_anchor(&parent->rx_submitted); >>> + spin_lock_init(&parent->tc_lock); >>> + INIT_DELAYED_WORK(&parent->timestamp, gs_usb_timestamp_work); >>> usb_set_intfdata(intf, parent); >>> parent->udev = udev; > >