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Wed, 8 Jul 2026 17:49:02 +0000 (GMT) Message-ID: Date: Wed, 8 Jul 2026 23:19:00 +0530 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3 6/6] null_blk: mark racy configfs attribute accesses with READ_ONCE/WRITE_ONCE To: Zizhi Wo , axboe@kernel.dk, dlemoal@kernel.org, kch@nvidia.com, johannes.thumshirn@wdc.com, kbusch@kernel.org, bvanassche@acm.org, linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org, yangerkun@huawei.com, chengzhihao1@huawei.com, wozizhi@huawei.com References: <20260708073917.2172392-1-wozizhi@huaweicloud.com> <20260708073917.2172392-7-wozizhi@huaweicloud.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260708073917.2172392-7-wozizhi@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=KsJ9H2WN c=1 sm=1 tr=0 ts=6a4e8d96 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=dK4PIHj8gR4ZtUvXNd0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA4MDE3NCBTYWx0ZWRfX4UXuSYxOCwbD iL6StaDPzXxHL/8FyGJ6VHCLBRauWpU6CxyJrUbnMWIhR01/Lxv39EsCsmwV4Y9qH0o15Gyn+51 gyZpjSpVwcqjq0S7oUKG9LxRx4nPyqo= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA4MDE3NCBTYWx0ZWRfXzOawZxBRTt2L YsMOgqCjf59k3AQqtaAHx8gjnmdbIubxFE+tG4vGDuG6T0qGoHjcb3SbvuiaV/LBbmY9P7UcQSM X+x0z6HnfDYrzRKnEmcLg9s3k9l5wtdrJEfGV/DROI8b+6UQWK64HkL9oP0vWGaYNN7VXZ7gSMP w/5ddfGDlH8aNuf/yTZ+ikkZ0SCG0Stqg1DmyyO0l1WNw477RIbfiybhDzXo3a+SX3xyhgiuxhQ GMROOx+Ru0xr49YowLocw+TxCEn1dtkMecTa61hToaV1eBDWdfs2GE/HGt3SHyUwmk924VH2TU7 9ytn3C4mahYbxVahTUViLxCndxZLsk06/ouCcDG6sYLEz8s7jWCJ6M8A6GxA8g60Ha9e1R9+YJf 1pv24aOv7jCRJgPZvJe11sr1fGyHsa1twqGimylXcZf6YSvm5uVw3JPADIlQYD7txxN6H3IoPz6 EAkxkMogLOqGnvg+Wcg== X-Proofpoint-ORIG-GUID: IiGPVPHIBVQOIY1x411ORtzCCOXn_zzB X-Proofpoint-GUID: IiGPVPHIBVQOIY1x411ORtzCCOXn_zzB X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-08_03,2026-07-08_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607080174 On 7/8/26 1:09 PM, Zizhi Wo wrote: > diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c > index 9e0002e4aeec..fd3c993a67b2 100644 > --- a/drivers/block/null_blk/main.c > +++ b/drivers/block/null_blk/main.c > @@ -346,7 +346,7 @@ static ssize_t \ > nullb_device_##NAME##_show(struct config_item *item, char *page) \ > { \ > return nullb_device_##TYPE##_attr_show( \ > - to_nullb_device(item)->NAME, page); \ > + READ_ONCE(to_nullb_device(item)->NAME), page); \ > } \ > static ssize_t \ > nullb_device_##NAME##_store(struct config_item *item, const char *page, \ > @@ -366,7 +366,7 @@ nullb_device_##NAME##_store(struct config_item *item, const char *page, \ > else if (test_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags)) \ > ret = -EBUSY; \ > if (!ret) \ > - dev->NAME = new_value; \ > + WRITE_ONCE(dev->NAME, new_value); \ > mutex_unlock(&lock); \ > if (ret < 0) \ > return ret; \ So in this series I see that all attribute _store() methods are now protected by the file-scoped mutex, which wasn't the case before. If this is intentional, have you considered protecting _show() with the same mutex as well? If yes, then that would avoid the lockless read/write races without requiring the additional READ_ONCE()/WRITE_ONCE() annotations throughout the code. Since these configfs attribute accesses are not on the I/O hot path, taking the mutex in _show() also seems acceptable from a performance perspective. Earlier in the previous series, I suggested using READ_ONCE/WRITE_ONCE because only _store() methods using apply_fn attributes were using the lock but that's not the case now. Thanks, --Nilay