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Mon, 16 Mar 2026 09:32:08 +0000 (GMT) Message-ID: <5984dfd9-04ae-4387-9a2e-f995b0781b92@linux.ibm.com> Date: Mon, 16 Mar 2026 15:02:07 +0530 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] blk-wbt: remove WARN_ON_ONCE from wbt_init_enable_default() To: Yuto Ohnuki , Jens Axboe Cc: Yu Kuai , Ming Lei , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com References: <20260316070358.65225-2-ytohnuki@amazon.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260316070358.65225-2-ytohnuki@amazon.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Bm2j9v2_8hUmvxhGeSyN-p7tmPZP5deo X-Authority-Analysis: v=2.4 cv=KajfcAYD c=1 sm=1 tr=0 ts=69b7ce1d cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=edf1wS77AAAA:8 a=hSkVLCK3AAAA:8 a=vggBfdFIAAAA:8 a=VnNF1IyMAAAA:8 a=OD0D0cZe8JJ7Gqt4sUkA:9 a=QEXdDO2ut3YA:10 a=DcSpbTIhAlouE1Uv7lRv:22 a=cQPPKAXgyycSBL8etih5:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE2MDA3MCBTYWx0ZWRfX1jGNAElkdR2L SCKWA12qEgX2S1ZwRM+giKQgJk9udXaWFbQAwcPcQSVi962f9NN6tgAscpgN1+QvMF2CSQos+wA F5fCR5LaNpeTqvIOSmYIXcELguL7fWvEeq5h7zV+IwTVhpNgNHYkhMET5nVFfOF4ZC/UGMAyNWE wWLhXBQQ/90q1SFng9QMCGQyGeajpDUjhuUydhqvcvSHjkbV5uGPHI4AusqV+yoKHUfFffJ1Yc3 bmIUDpKS3hQkq7wiNgwy5cHZOgh5rjsI5tmUIXEDqTZNKdq0KacOjskmFrjIInr/Iffr8GJwKcP 3gFNs+JRcHMZygGZI3iyDy2f/qF08smm9CM3XRYyn4m8qj8vsPGEHHDXXH4rKQPV/9kzaMfN7u5 2QjHsNIrveA/hfXI1DUzdhv2jwgWlt1JwSHMlPs4AGB4CPkSdX2k32oSz0T04gQVJqb1CIl2HQS p0MKXmiEHp4d9DMFkJA== X-Proofpoint-GUID: Bm2j9v2_8hUmvxhGeSyN-p7tmPZP5deo X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-16_03,2026-03-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 spamscore=0 malwarescore=0 clxscore=1011 impostorscore=0 bulkscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603160070 On 3/16/26 12:33 PM, Yuto Ohnuki wrote: > wbt_init_enable_default() uses WARN_ON_ONCE to check for failures from > wbt_alloc() and wbt_init(). However, both are expected failure paths: > > - wbt_alloc() can return NULL under memory pressure (-ENOMEM) > - wbt_init() can fail with -EBUSY if wbt is already registered > > syzbot triggers this by injecting memory allocation failures during MTD > partition creation via ioctl(BLKPG), causing a spurious warning. > > wbt_init_enable_default() is a best-effort initialization called from > blk_register_queue() with a void return type. Failure simply means the > disk operates without writeback throttling, which is harmless. > > Replace WARN_ON_ONCE with plain if-checks, consistent with how > wbt_set_lat() in the same file already handles these failures. Add a > pr_warn() for the wbt_init() failure to retain diagnostic information > without triggering a full stack trace. > > Reported-by:syzbot+71fcf20f7c1e5043d78c@syzkaller.appspotmail.com > Closes:https://syzkaller.appspot.com/bug?extid=71fcf20f7c1e5043d78c > Fixes: 41afaeeda509 ("blk-wbt: fix possible deadlock to nest pcpu_alloc_mutex under q_usage_counter") > Signed-off-by: Yuto Ohnuki Looks good to me: Reviewed-by: Nilay Shroff