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b=B1yzwcN7CWiyNWpcvubXRrCbxuNfue3EMWaxmI3o8yCwa1dApj+/hy+6VaZvzbFwj gEiGdceIHEoatSvdxVZYydAj6jRnOYabrYDeBySkuosbTg1kwo0jFsSP59YwWge8Fh vUK638xS1loXo8ZXokQ+5An9IkLHb3WpMcTzQ3KsL0J8WrjSZcRZhAoPTl6T2kttoz rdkBGDeGBcS3zMVvm8FyuDJ2cPNbXIXbrVQhwpQZhqqSn2Json5EKJTKee4s6G1RTm tpxiF8y58k6WRTbQocwVUIseU94DsGbwghXbH7zHPKxEd/jWAiuBKsm5tltGI3Ev+r CvokGvV5slJGw== Date: Tue, 3 Nov 2026 14:51:52 +0000 From: Harry Yoo To: "Vlastimil Babka (SUSE)" Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Alexei Starovoitov , Pedro Falcato , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH RFC 4/4] mm/slab: serialize defer_free_barrier() Message-ID: References: <20260624-kmalloc-nolock-fixes-v1-0-fdf4d17351dd@kernel.org> <20260624-kmalloc-nolock-fixes-v1-4-fdf4d17351dd@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: afju5okrzqz8up48fxdhxny3jjffeyn9 X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 56EECC0003 X-HE-Tag: 1793717515-891949 X-HE-Meta: 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 6vE1fGzt fabGXq2THpwIzxO8lA31sy5TmdYgEhzP8c2VSwAUIrSTclH65m7IhmH9zrNsvSBksKv9JcFFvtjhlD0HUKKbDlWOrg0+119yW8l989Xq1IJE1liwa7XjZw8JHZV9AiITFxFv+Hd8jLYbLC8rKlW/Xhe0Uiz+Wmp/zggvpYLigUFvQPSeGtYt3f2obUYYrCJRLOD5dX+lk3XLio7QiwciaHZf5yYhSky6roH2oEoM0E1ju3A3ld2xxIjDBzKtdCSmX9+yBfTDVYDtxBdFy4GaMw+RiaHN7PvfM+AqzFtjUhDR/qOHaBbHXs9dSQek2rqob8FsDZ6T/dGqv+Xl3MPzbsuj0k3JzK0n3dcLNXoLTpAmcy4DCHo5iP5JC8SfOLCFB/6sd 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 Fri, Jun 26, 2026 at 05:00:51PM +0200, Vlastimil Babka (SUSE) wrote: > On 6/24/26 15:11, Harry Yoo (Oracle) wrote: > > irq_work_sync() uses rcuwait instead of busy waiting in two cases: > > > > 1. The kernel is using PREEMPT_RT and the irq work does not run in a > > hardirq context. > > > > 2. The architecture cannot send inter-processor interrupts to make > > busy waiting reasonably short. > > > > However, rcuwait.h says: > >> The caller is responsible for locking around rcuwait_wait_event(), > >> and [prepare_to/finish]_rcuwait() such that writes to @task are > >> properly serialized. > > > > Since defer_free_barrier() calls irq_work_sync() without any locks, > > it can potentially cause a hang as writes to @task are not serialized. > > > > Fix this by calling defer_free_barrier() under slab_mutex and > > cpus_read_lock() and add lockdep asserts. > > > > Now that defer_free_barrier() is called inside cpus_read_lock(), iterate > > over online cpus instead of possible cpus. > > > > Reported-by: Sashiko > > Closes: https://sashiko.dev/#/patchset/20260615-kfree_rcu_nolock-v3-0-70a54f3775bb%40kernel.org?part=5 > > Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") > > Cc: stable@vger.kernel.org > > Signed-off-by: Harry Yoo (Oracle) > > Acked-by: Vlastimil Babka (SUSE) It was dropped as it now introduces a mutex. (codetag_unload_module() invokes kvfree_rcu_barrier() -> deferred_work_barrier() but doesn't have access to slab_mutex so we can't reuse it.) -- Cheers, Harry / Hyeonggon