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Wed, 5 Nov 2025 06:54:02 +0000 (GMT) Message-ID: Date: Wed, 5 Nov 2025 12:24:00 +0530 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [bug report] fstests generic/085 btrfs hang with use-after-free at bdev_super_lock To: Shinichiro Kawasaki , "linux-block@vger.kernel.org" Cc: "linux-fsdevel@vger.kernel.org" References: Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: udrflgboVtG4Ikl1yGaWkSVzHEZVTTFX X-Proofpoint-ORIG-GUID: udrflgboVtG4Ikl1yGaWkSVzHEZVTTFX X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTAxMDAyMSBTYWx0ZWRfX54Kf18vUpkfq EPH90OZY5n4r3Mt8s8W/td22KKfurh8k59kqTpmTnVe0xt+pJDyQUtntiBqx8Yape9UfP6hog7k d25NeVjQgzyU9Vk6Hsd5ovjW/fAulwQ51etq0WL2j/iuxvInOSNaZHNVxy7rchSqG6PMT4vo1kB z4gs8sJaEYfNN5VDKkH8gpTSjgGDUPFmBjCmOO4tLbp5nHgE7QHnFOmThpvN57+1DNfdCWlxi8E AV5BelXeBf7ddbbfFv6vcw0ESsp41aScKMzFo8+vfkIrIgjpCYz9lJK5858GA4GGVs/az2KF3Ue KBEzCjoM5JaNSC82MimLFL85pBdLoWwgSzMZck1H1Qp1OBpYieaPqvGWY/DA6+MGDUvWNCy3U3S fz2YcWk3NqV0jhnpQAwFNphJauxRIQ== X-Authority-Analysis: v=2.4 cv=H8HWAuYi c=1 sm=1 tr=0 ts=690af48c cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=_FWC9dmBtg7OGuMU_m4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-05_03,2025-11-03_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 adultscore=0 impostorscore=0 clxscore=1015 bulkscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511010021 Hi Shinichiro, On 11/5/25 6:31 AM, Shinichiro Kawasaki wrote: > When I run fstests for btrfs on regular null_blk devices, I observe KASAN > slab-use-after-free in bdev_super_lock() followed by kernel hang. I observed it > for the kernel v6.17-rc4 for the first time. And I still observe it for the > latest kernel v6.18-rc4. > > The hang is recreated when I prepare eight of 5Gib size null_blk devices, assign > one for TEST_DEV, and assign the other seven for SCRATCH_DEV_POOl. The hang > happens at generic/085. It is sporadic. When I repeat the test case g085 only, > the hang is not recreated. But when I repeat the whole fstests a few times, the > hang is recreated in stable manner. It takes several hours to recreate the hang. > > I spent some weeks to bisect, and found the trigger commit is this: > > 370ac285f23a ("block: avoid cpu_hotplug_lock depedency on freeze_lock") > > The commit was included in the kernel tag v6.17-rc3. When I reverted the commit > from v6.17-rc3, the hang disappeared (I repeated the whole fstests 5 times on > two test nodes, and did not observe the hang). I'm not sure if the commit > created the problem cause or revealed the hidden problem. Thanks for the report! This doesn't seem to be caused due to 370ac285f23a ("block: avoid cpu_hotplug_lock depedency on freeze_lock"). However it appears that we're hitting a race while freezing/unfreezing filesystem. It'd better if someone from fs team can take a look at it. Thanks, --Nilay