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Fri, 06 Nov 2026 08:00:38 +0000 X-Mizu-Trace-ID: 9a35c9af166ee30d X-Migadu-Flow: FLOW_OUT Date: Fri, 6 Nov 2026 16:00:31 +0800 From: Hao Li To: Harry Yoo Cc: Zhan Xusheng , vbabka@kernel.org, urezki@gmail.com, paulmck@kernel.org, qiang.zhang@linux.dev, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, zhanxusheng@xiaomi.com Subject: Re: [PATCH 2/2] mm/slab: don't queue the page cache work under krcp->lock Message-ID: References: <20261028134647.3176080-1-zhanxusheng1024@gmail.com> <20261028134647.3176080-2-zhanxusheng1024@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: ed6s4znh9y596zqgzxrh8ugk7t8wuofb X-Rspamd-Queue-Id: F3B9B4000D X-Rspam-User: X-HE-Tag: 1793952039-160961 X-HE-Meta: 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 SN5jWCIV o7Lk6MvJlT6XbbKThhvVKLKNf6RpiKRyZVa3kzShYmEpkClKupPtp45wAmUloWgJvjbQoeacexh7hnimsaKiUr211OMxLSG1uPFWIpBEgCSbwi6YLJdEYzx5dEvsQy1pl1RBF/kaKArkza64Ud2ckybp+/a8ugFKzSXM23NHZNjXWgjgxjha9mqpkvwYGPgLHUzdq+IblkDMrFC7OGdQxZJrBzmEX0/n5wQyh8iBrJtpfwvEW8qm0tp4WKiXI9fNVEPysxeZ/e0gskPYhFt9c3pK2vMrYEf+eQSdXr3WO1G0WOjKORi6+7ae6EvTtTAjWcwBF1pOcbVXCHAtkVO81g9f217NDSvqgSKhtXsvFlJTGJY6gLR7jLUkNnvQx2nQdoWyvTJb3QWextqIm8CB7vVtA9JRASYQdPHRjGfZYnVFnjPY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Nov 02, 2026 at 02:35:40PM +0000, Harry Yoo wrote: > Here I added bit more context and adjusted comment. End result: > > mm/slab: don't queue the page cache work under krcp->lock > > Commit 56292e8609e3 ("rcu/tree: Defer kvfree_rcu() allocation to a > clean context") deferred page allocations to a workqueue. To avoid > deadlocks with the scheduler, it used hrtimer to queue the work instead > of queueing it directly. > > Commit d0bfa8b3c411 ("kvfree_rcu: Release a page cache under memory > pressure") later added a backoff mechanism under memory pressure, but > did not consider that queue_delayed_work() with delay = 0 immediately > queues the work and introduced the deadlock commit 56292e8609e3 tried to > avoid. > > run_page_cache_worker() runs under krcp->lock, from kvfree_call_rcu() > callers that may hold more, such as set_cpus_allowed_force() under > pi_lock, so it kicks the refill work from an hrtimer. Under memory > pressure it instead queues the work with a delay of > rcutree.rcu_delay_page_cache_fill_msec, which may be 0, and a zero delay > queues it at once, taking pool->lock under krcp->lock. > > With the delay set to 0, calling kvfree_rcu() on vmalloc memory under > pi_lock after a drop_caches makes lockdep report: > > Chain exists of: > &pool->lock --> &p->pi_lock --> krc.lock > > Use the hrtimer when the delay is 0. > > Fixes: d0bfa8b3c411 ("kvfree_rcu: Release a page cache under memory pressure") > Cc: stable@vger.kernel.org > Signed-off-by: Zhan Xusheng > Link: https://patch.msgid.link/20261028134647.3176080-2-zhanxusheng1024@gmail.com > [ harry@kernel.org: add more context to changelog and adjust comment ] > Signed-off-by: Harry Yoo (Meta) > --- > mm/slab_common.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) Reviewed-by: Hao Li -- Thanks, Hao