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From: Johannes Berg To: Tejun Heo Cc: Ben Greear , linux-wireless , "Korenblit, Miriam Rachel" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Tue, 03 Mar 2026 22:12:12 +0100 In-Reply-To: References: <18c4bfed-caca-bef3-a139-63d7fa48940a@candelatech.com> <3456b2c89f057900b39ce79ea8ca1154c5014e43.camel@sipsolutions.net> <0de6c8d1-d2fa-44ac-8025-cfcfecd87b02@candelatech.com> <35779061f94c2a55bb58dcd619ae91c618509cf4.camel@sipsolutions.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) MIME-Version: 1.0 X-malware-bazaar: not-scanned X-Rspamd-Queue-Id: C08D41C0002 X-Stat-Signature: nanq83t7394wy91az993geynoktfrmfr X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1772572335-214489 X-HE-Meta: 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 2l7fWibG xXB/HlWs5n25hvsMs6bGzl89FH86DTt1gTs1S8npbK6yzsLur0KHVKpN/C5CIlj8P/0U8VprIqGUBB36jlL1/gEjzye5Q3YBxd0qnoD8MjqanpdnS9L+gd8qI2oAYB3ETrxVWnHv05W2uOrgGVjfvQ8XEpXV+7RMs573NUAydOYTfc3dVfdIaaAUfsfeInGYCKgQHyu0eoyDKTeN+5YcjQPBwOUoUp7L5Z+KlfdUerv2a7Uw0gLUy0olnag== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2026-03-03 at 10:52 -1000, Tejun Heo wrote: > Hello, >=20 > On Tue, Mar 03, 2026 at 12:49:24PM +0100, Johannes Berg wrote: > > Fair. I don't know, I don't think there's anything that even shows that > > there's a dependency between the two workqueues and the > > "((wq_completion)events_unbound)" and "((wq_completion)events)", and > > there would have to be for it to deadlock this way because of that? > >=20 > > But one is mm_percpu_wq and the other is system_percpu_wq. > >=20 > > Tejun, does the workqueue code somehow introduce a dependency between > > different per-CPU workqueues that's not modelled in lockdep? >=20 > Hopefully not. Kinda late to the party. Why isn't mm_percpu_wq making > forward progress? That should in all circumstances. What's the work item = and > kworker doing? Oh and in addition: the worker that's kicked off by __lru_add_drain_all() doesn't really seem to do anything long-running? It's lru_add_drain_per_cpu(), which is lru_add_and_bh_lrus_drain(), which would appear to be entirely non-sleepable code (holding either local locks or having irqs disabled.) It also doesn't show up in the log, apparently, hence my question about strange dependencies. johannes