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Mon, 16 Jun 2025 02:29:30 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHsUd2qFGuMXKuccZvrFk7CIMKUwpb0xUUFf9RE6u/Crka9A/TnucG3IcOlzpJlwgNnMDfteA== X-Received: by 2002:a17:90b:2b45:b0:313:b1a:3939 with SMTP id 98e67ed59e1d1-313f1cdaa59mr15010915a91.15.1750066169791; Mon, 16 Jun 2025 02:29:29 -0700 (PDT) Received: from [10.152.204.131] ([202.46.23.19]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-313c1b6d56bsm9195325a91.46.2025.06.16.02.29.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jun 2025 02:29:29 -0700 (PDT) Message-ID: <63c2c889-0a09-4b25-a1d2-2aaa92d75d9f@oss.qualcomm.com> Date: Mon, 16 Jun 2025 14:59:24 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] wifi: ath12k: fix dest ring-buffer corruption To: Baochen Qiang , Johan Hovold , P Praneesh Cc: Johan Hovold , Jeff Johnson , Miaoqing Pan , Remi Pommarel , linux-wireless@vger.kernel.org, ath12k@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250604144509.28374-1-johan+linaro@kernel.org> <20250604144509.28374-2-johan+linaro@kernel.org> <6f3eb9fa-617e-4434-8fc4-33dd92c4bdd2@quicinc.com> Content-Language: en-US From: Praneesh P In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjE2MDA2MSBTYWx0ZWRfX+mijjBE7TLSQ yof0NnvuWB4YY2IZigYzKn8DgqlXEvnOz2SuttVvT2/OxsQg0K9vnO7XZ4KXFRCbKfA/k3mymh7 w12gy5iXUsKay2d+Bb9UQDXgQwf74FVPjaTaQGYK4Ib0hMvp+YPr+TEeuOqgQQo27QITogAGz+p 8y4p1BZ8ELRjabnDtMe7GyomO78b6P/GfuC28Rx88mfLQYv1ibZSwvMLfstNmYx2fwrXtwmehaB tpoMiFMXF/DXSPe/68BSJC5JS6uoMdhee+4x51VSzgDdnvPXHNEXz3VuLjrCo+7a+TEfpQEIPTA N2EJyGFPu2WVmVOgtmFdTSWZz9KVI4RKnI4NnhCvg7sImUw9hStbucSK/SrR8TWo5jrcj8aPKGV zWrVH/CGnP0BmKPU5KPbNM4s4Cyg+tZG8lYUG4Xaq5RkOlKbnhN4IVtBxDSySOdH+8mX1WHQ X-Proofpoint-GUID: pxxCvKfyuQBXe4Bw1p1rtxEO5HyMiBbd X-Proofpoint-ORIG-GUID: pxxCvKfyuQBXe4Bw1p1rtxEO5HyMiBbd X-Authority-Analysis: v=2.4 cv=FrIF/3rq c=1 sm=1 tr=0 ts=684fe3fb cx=c_pps a=UNFcQwm+pnOIJct1K4W+Mw==:117 a=j4ogTh8yFefVWWEFDRgCtg==:17 a=IkcTkHD0fZMA:10 a=6IFa9wvqVegA:10 a=Ske-G14cY86dgNt0HIsA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=uKXjsCUrEbL0IQVhDsJ9:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-06-16_04,2025-06-13_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 suspectscore=0 spamscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 mlxlogscore=999 bulkscore=0 impostorscore=0 malwarescore=0 phishscore=0 mlxscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2506160061 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250616_022934_071378_D036FCB7 X-CRM114-Status: GOOD ( 26.37 ) X-BeenThere: ath12k@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "ath12k" Errors-To: ath12k-bounces+ath12k=archiver.kernel.org@lists.infradead.org On 6/5/2025 4:19 PM, Baochen Qiang wrote: > > On 6/5/2025 6:00 PM, Johan Hovold wrote: >> On Thu, Jun 05, 2025 at 04:41:32PM +0800, Baochen Qiang wrote: >>> On 6/4/2025 10:45 PM, Johan Hovold wrote: >>>> Add the missing memory barrier to make sure that destination ring >>>> descriptors are read after the head pointers to avoid using stale data >>>> on weakly ordered architectures like aarch64. >>>> >>>> The barrier is added to the ath12k_hal_srng_access_begin() helper for >>>> symmetry with follow-on fixes for source ring buffer corruption which >>>> will add barriers to ath12k_hal_srng_access_end(). >>>> >>>> Note that this may fix the empty descriptor issue recently worked around >>>> by commit 51ad34a47e9f ("wifi: ath12k: Add drop descriptor handling for >>>> monitor ring"). >>> why? I would expect drunk cookies are valid in case of HAL_MON_DEST_INFO0_EMPTY_DESC, >>> rather than anything caused by reordering. >> Based on a quick look it seemed like this could possibly fall in the >> same category as some of the other workarounds I've spotted while >> looking into these ordering issues (e.g. f9fff67d2d7c ("wifi: ath11k: >> Fix SKB corruption in REO destination ring")). >> >> If you say this one is clearly unrelated, I'll drop the comment. > Praneesh, could you comment here since you made that change? Empty/Drop descriptor is intentionally issued by the hardware during backpressure scenario and is unrelated to the issue discussed in this patch series. >>>> @@ -343,9 +343,6 @@ static int ath12k_ce_completed_recv_next(struct ath12k_ce_pipe *pipe, >>>> goto err; >>>> } >>>> >>>> - /* Make sure descriptor is read after the head pointer. */ >>>> - dma_rmb(); >>>> - >>>> *nbytes = ath12k_hal_ce_dst_status_get_length(desc); >>>> >>>> *skb = pipe->dest_ring->skb[sw_index]; >>>> diff --git a/drivers/net/wireless/ath/ath12k/hal.c b/drivers/net/wireless/ath/ath12k/hal.c >>>> index 91d5126ca149..9eea13ed5565 100644 >>>> --- a/drivers/net/wireless/ath/ath12k/hal.c >>>> +++ b/drivers/net/wireless/ath/ath12k/hal.c >>>> @@ -2126,13 +2126,24 @@ void *ath12k_hal_srng_src_get_next_reaped(struct ath12k_base *ab, >>>> >>>> void ath12k_hal_srng_access_begin(struct ath12k_base *ab, struct hal_srng *srng) >>>> { >>>> + u32 hp; >>>> + >>>> lockdep_assert_held(&srng->lock); >>>> >>>> - if (srng->ring_dir == HAL_SRNG_DIR_SRC) >>>> + if (srng->ring_dir == HAL_SRNG_DIR_SRC) { >>>> srng->u.src_ring.cached_tp = >>>> *(volatile u32 *)srng->u.src_ring.tp_addr; >>>> - else >>>> - srng->u.dst_ring.cached_hp = READ_ONCE(*srng->u.dst_ring.hp_addr); >>>> + } else { >>>> + hp = READ_ONCE(*srng->u.dst_ring.hp_addr); >>>> + >>>> + if (hp != srng->u.dst_ring.cached_hp) { >>> This consumes additional CPU cycles in hot path, which is a concern to me. >>> >>> Based on that, I prefer the v1 implementation. >> The conditional avoids a memory barrier in case the ring is empty, so >> for all callers but ath12k_ce_completed_recv_next() it's an improvement >> over v1 in that sense. >> >> I could make the barrier unconditional, which will only add one barrier >> to ath12k_ce_completed_recv_next() in case the ring is empty compared to >> v1. Perhaps that's a good compromise if you worry about the extra >> comparison? > I guess the unconditional barrier also has impact on performance? If so I am not sure > which one is better then ... > > Let's just keep it as is and see what others think. > >> I very much want to avoid having both explicit barriers in the caller >> and barriers in the hal end() helper. I think it should be either or. >> >>>> + srng->u.dst_ring.cached_hp = hp; >>>> + /* Make sure descriptor is read after the head >>>> + * pointer. >>>> + */ >>>> + dma_rmb(); >>>> + } >>>> + } >> Johan >