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Howlett (Google)" Cc: Andrew Morton , Thomas Graf , Herbert Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org, Lorenzo Stoakes , Chris Mason , Alice Ryhl , Andrew Ballance , stable@vger.kernel.org, "David Hildenbrand (Arm)" Subject: Re: [PATCH 4/4] rhashtable: fix vmalloc() deadlock in atomic rehash Message-ID: References: <20261028154218.1668182-1-liam@infradead.org> <20261028154218.1668182-5-liam@infradead.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261028154218.1668182-5-liam@infradead.org> X-Rspamd-Queue-Id: 2EB968000A X-Stat-Signature: tzciddwpto8w3kpqu1upfyyhecismrkc X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793304155-377229 X-HE-Meta: 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 NsnMmimP baXZ0JMfqa8xMiG+XJUgXA7kMexMCiTgc+wsKUnPOisRlicllISoSBeXNIYfsuInnSq4RTBbtjZ79KfPbYkCT38jxeaYCzbEnw8cpJRMmNbURx6RSdZt2RP2BQL4ooRAHp3FiqiRD1h28xuJiPhyv/rZb8NlI144F+W2tIf1k49e1Z72S1vuj9jqQWO7RyqxzvLcTPxWXSf5Eo36F7f4GOLCtKw06tV37lfZsQTzZi5x02tpHh2qks0OBdg== 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 Wed, Oct 28, 2026 at 11:42:18AM -0400, Liam R. Howlett (Google) wrote: > Below, one CPU adds an FDB entry for an RTM_NEWNEIGH netlink request, > while another CPU is inside vmalloc() or vfree(): > > RTM_NEWNEIGH vmalloc() or vfree() > ============ ==================== > spin_lock_bh(&br->hash_lock) > spin_lock(&vn->busy.lock) > rhashtable_insert_rehash() > kvmalloc(GFP_ATOMIC) > vmalloc() > spin_lock(&vn->busy.lock) > waits for the other CPU > softirq: a frame for the bridge > spin_lock(&br->hash_lock) > waits for RTM_NEWNEIGH This seems like the kind of deadlock that lockdep can catch. Why hasn't it? Do we need to add a fake lock for RTM_NEWNEIGH?