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Thu, 13 Mar 2025 01:41:56 +0000 (GMT) Received: from nalasex01c.na.qualcomm.com (nalasex01c.na.qualcomm.com [10.47.97.35]) by NALASPPMTA04.qualcomm.com (8.18.1.2/8.18.1.2) with ESMTPS id 52D1fudv015335 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Mar 2025 01:41:56 GMT Received: from [10.239.29.24] (10.80.80.8) by nalasex01c.na.qualcomm.com (10.47.97.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.9; Wed, 12 Mar 2025 18:41:54 -0700 Message-ID: <8251fc50-5df4-4a3f-91bf-40c09c33cf6e@quicinc.com> Date: Thu, 13 Mar 2025 09:41:51 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 ath-next 2/2] wifi: ath11k: fix HTC rx insufficient length To: Johan Hovold CC: Jeff Johnson , , , , References: <20250310010217.3845141-1-quic_miaoqing@quicinc.com> <20250310010217.3845141-3-quic_miaoqing@quicinc.com> <7b1c5e40-b11d-421b-8c8b-117a2a53298b@quicinc.com> <72d95d77-674e-4ae7-83b0-ab58748b8251@quicinc.com> Content-Language: en-US From: Miaoqing Pan In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nalasex01c.na.qualcomm.com (10.47.97.35) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: pWY8Qf7XDFYmi1Uu1LG3_sLpgHo3SVBs X-Authority-Analysis: v=2.4 cv=I+llRMgg c=1 sm=1 tr=0 ts=67d237e5 cx=c_pps a=ouPCqIW2jiPt+lZRy3xVPw==:117 a=ouPCqIW2jiPt+lZRy3xVPw==:17 a=GEpy-HfZoHoA:10 a=IkcTkHD0fZMA:10 a=Vs1iUdzkB0EA:10 a=VwQbUJbxAAAA:8 a=COk6AnOGAAAA:8 a=POYSu9ou3bP9OeXHj2YA:9 a=QEXdDO2ut3YA:10 a=TjNXssC_j7lpFel5tvFf:22 X-Proofpoint-GUID: pWY8Qf7XDFYmi1Uu1LG3_sLpgHo3SVBs X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1093,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-13_01,2025-03-11_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 lowpriorityscore=0 adultscore=0 clxscore=1015 impostorscore=0 priorityscore=1501 spamscore=0 malwarescore=0 mlxscore=0 suspectscore=0 phishscore=0 bulkscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2503130011 On 3/13/2025 12:43 AM, Johan Hovold wrote: > On Wed, Mar 12, 2025 at 09:11:45AM +0800, Miaoqing Pan wrote: >> On 3/11/2025 11:20 PM, Jeff Johnson wrote: >>> On 3/11/2025 1:29 AM, Miaoqing Pan wrote: >>>> On 3/10/2025 6:09 PM, Johan Hovold wrote: >>>>> I'm still waiting for feedback from one user that can reproduce the >>>>> ring-buffer corruption very easily, but another user mentioned seeing >>>>> multiple zero-length descriptor warnings over the weekend when running >>>>> with this patch: >>>>> >>>>> ath11k_pci 0006:01:00.0: rxed invalid length (nbytes 0, max 2048) >>>>> >>>>> Are there ever any valid reasons for seeing a zero-length descriptor >>>>> (i.e. unrelated to the race at hand)? IIUC the warning would only be >>>>> printed when processing such descriptors a second time (i.e. when >>>>> is_desc_len0 is set). >>>> >>>> That's exactly the logic, only can see the warning in a second time. For >>>> the first time, ath12k_ce_completed_recv_next() returns '-EIO'. >>> >>> That didn't answer Johan's first question: >>> Are there ever any valid reasons for seeing a zero-length descriptor? >> >> The events currently observed are all firmware logs. The discarded >> packets will not affect normal operation. I will adjust the logging to >> debug level. > > That still does not answer the question whether there are ever any valid > reasons for seeing zero-length descriptors. I assume there are none? > >>> We have an issue that there is a race condition where hardware updates the >>> pointer before it has filled all the data. The current solution is just to >>> read the data a second time. But if that second read also occurs before >>> hardware has updated the data, then the issue isn't fixed. >> >> Thanks for the addition. >> >>> So should there be some forced delay before we read a second time? >>> Or should we attempt to read more times? >> >> The initial fix was to keep waiting for the data to be ready. The >> observed phenomenon is that when the second read fails, subsequent reads >> will continue to fail until the firmware's CE2 ring is full and triggers >> an assert after timeout. However, this situation is relatively rare, and >> in most cases, the second read will succeed. Therefore, adding a delay >> or multiple read attempts is not useful. > > The proposed fix is broken since ath11k_hal_ce_dst_status_get_length() > not just reads the length but also sets it to zero so that the updated > length may indeed never be seen. > Good point! > I've taken a closer look at the driver and it seems like we're missing a > read barrier to make sure that the updated descriptor is not read until > after the head pointer. > > Miaoqing, could you try the below patch with your reproducer and see if > it is enough to fix the corruption? > Sure, the stress test is running. > If so I can resend with the warning removed and include a corresponding > fix for ath12k (it looks like there are further places where barriers > are missing too). > > Johan > > If the DMA read barrier works, do you think my submitted patch series is still needed? Because the error handling is incorrect. > From 656dbd0894741445aeb16ee8357e6fef51b6084c Mon Sep 17 00:00:00 2001 > From: Johan Hovold > Date: Wed, 12 Mar 2025 16:49:20 +0100 > Subject: [PATCH] wifi: ath11k: fix ring-buffer corruption > > Users of the Lenovo ThinkPad X13s have reported that Wi-Fi sometimes > breaks and the log fills up with errors like: > > ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1484, expected 1492 > ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1460, expected 1484 > > which based on a quick look at the driver seemed to indicate some kind > of ring-buffer corruption. > > Miaoqing Pan tracked it down to the host seeing the updated destination > ring head pointer before the updated descriptor, and the error handling > for that in turn leaves the ring buffer in an inconsistent state. > > Add the missing the read barrier to make sure that the descriptor is > read after the head pointer to address the root cause of the corruption. > > The error handling can be fixed separately in case there can ever be > actual zero-length descriptors. > > FIXME: remove WARN_ON_ONCE() added for verification purposes > > Tested-on: WCN6855 hw2.1 WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41 > > Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices") > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218623 > Link: https://lore.kernel.org/20250310010217.3845141-3-quic_miaoqing@quicinc.com > Cc: Miaoqing Pan > Cc: stable@vger.kernel.org # 5.6 > Signed-off-by: Johan Hovold > --- > drivers/net/wireless/ath/ath11k/ce.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/net/wireless/ath/ath11k/ce.c b/drivers/net/wireless/ath/ath11k/ce.c > index e66e86bdec20..423b970e288c 100644 > --- a/drivers/net/wireless/ath/ath11k/ce.c > +++ b/drivers/net/wireless/ath/ath11k/ce.c > @@ -393,8 +393,12 @@ static int ath11k_ce_completed_recv_next(struct ath11k_ce_pipe *pipe, > goto err; > } > > + /* Make sure descriptor is read after the head pointer. */ > + dma_rmb(); > + > *nbytes = ath11k_hal_ce_dst_status_get_length(desc); > if (*nbytes == 0) { > + WARN_ON_ONCE(1); // FIXME: remove > ret = -EIO; > goto err; > }