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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CH1PEPF0000A345.mail.protection.outlook.com (10.167.244.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8534.20 via Frontend Transport; Mon, 24 Mar 2025 14:52:52 +0000 Received: from [10.252.90.31] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Mon, 24 Mar 2025 09:52:48 -0500 Message-ID: Date: Mon, 24 Mar 2025 20:22:40 +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: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter From: K Prateek Nayak To: Oleg Nesterov , Mateusz Guzik CC: syzbot , , , , , , , , , , References: <20250323184848.GB14883@redhat.com> <67e05e30.050a0220.21942d.0003.GAE@google.com> <20250323194701.GC14883@redhat.com> <20250323210251.GD14883@redhat.com> <7e377feb-a78b-4055-88cc-2c20f924bf82@amd.com> Content-Language: en-US In-Reply-To: <7e377feb-a78b-4055-88cc-2c20f924bf82@amd.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Mar 2025 14:52:52.1868 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 822d573b-dff0-4deb-455a-08dd6ae38d9d X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000A345.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR12MB7951 Hello folks, Some updates. On 3/24/2025 6:49 PM, K Prateek Nayak wrote: >> >> Per syzbot this attempt did not work out either. >> >> I think the blind stabs taken by everyone here are enough. >> >> The report does not provide the crucial bit: what are the other >> threads doing. Presumably someone else is stuck somewhere, possibly >> not even in pipe code and that stuck thread was supposed to wake up >> the one which trips over hung task detector. Figuring out what that >> thread is imo the next step. >> >> I failed to find a relevant command in >> https://github.com/google/syzkaller/blob/master/docs/syzbot.md >> >> So if you guys know someone on syzkaller side, maybe you can ask them >> to tweak the report *or* maybe syzbot can test a "fix" which makes >> hung task detector also report all backtraces? I don't know if that >> can work, the output may be long enough that it will get trimmed by >> something. >> >> I don't have to time work on this for now, just throwing ideas. > > I got the reproducer running locally. Tracing stuff currently to see > what is tripping. Will report back once I find something interesting. > Might take a while since the 9p bits are so far spread out. > So far, with tracing, this is where I'm: o Mainline + Oleg's optimization reverted: ... kworker/43:1-1723 [043] ..... 115.309065: p9_read_work: Data read wait 55 kworker/43:1-1723 [043] ..... 115.309066: p9_read_work: Data read 55 kworker/43:1-1723 [043] ..... 115.309067: p9_read_work: Data read wait 7 kworker/43:1-1723 [043] ..... 115.309068: p9_read_work: Data read 7 repro-4138 [043] ..... 115.309084: netfs_wake_write_collector: Wake collector repro-4138 [043] ..... 115.309085: netfs_wake_write_collector: Queuing collector work repro-4138 [043] ..... 115.309088: netfs_unbuffered_write: netfs_unbuffered_write repro-4138 [043] ..... 115.309088: netfs_end_issue_write: netfs_end_issue_write repro-4138 [043] ..... 115.309089: netfs_end_issue_write: Write collector need poke 0 repro-4138 [043] ..... 115.309091: netfs_unbuffered_write_iter_locked: Waiting on NETFS_RREQ_IN_PROGRESS! kworker/u1030:1-1951 [168] ..... 115.309096: netfs_wake_write_collector: Wake collector kworker/u1030:1-1951 [168] ..... 115.309097: netfs_wake_write_collector: Queuing collector work kworker/u1030:1-1951 [168] ..... 115.309102: netfs_write_collection_worker: Write collect clearing and waking up! ... (syzbot reproducer continues) o Mainline: kworker/185:1-1767 [185] ..... 109.485961: p9_read_work: Data read wait 7 kworker/185:1-1767 [185] ..... 109.485962: p9_read_work: Data read 7 kworker/185:1-1767 [185] ..... 109.485962: p9_read_work: Data read wait 55 kworker/185:1-1767 [185] ..... 109.485963: p9_read_work: Data read 55 repro-4038 [185] ..... 114.225717: netfs_wake_write_collector: Wake collector repro-4038 [185] ..... 114.225723: netfs_wake_write_collector: Queuing collector work repro-4038 [185] ..... 114.225727: netfs_unbuffered_write: netfs_unbuffered_write repro-4038 [185] ..... 114.225727: netfs_end_issue_write: netfs_end_issue_write repro-4038 [185] ..... 114.225728: netfs_end_issue_write: Write collector need poke 0 repro-4038 [185] ..... 114.225728: netfs_unbuffered_write_iter_locked: Waiting on NETFS_RREQ_IN_PROGRESS! ... (syzbot reproducer hangs) There is a third "kworker/u1030" component that never gets woken up for reasons currently unknown to me with Oleg's optimization. I'll keep digging. -- Thanks and Regards, Prateek