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[217.213.144.15]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5bfca5bb57asm1109637e87.74.2026.10.29.03.08.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 03:08:13 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 29 Oct 2026 11:08:10 +0100 To: Herbert Xu Cc: "Liam R. Howlett (Google)" , Uladzislau Rezki , Michal Hocko , Baoquan He , Alexander Potapenko , Andrey Ryabinin , Marco Elver , Michal Hocko , Linux Crypto Mailing List , Andrew Morton , Thomas Graf , 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: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3D53916000A X-Stat-Signature: ijzz71aoqih4qza1861wnsu4cshk3hiy X-Spam-Status: No, score=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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-HE-Tag: 1793268496-599956 X-HE-Meta: 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 r4z/GWRF 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 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 Thu, Oct 29, 2026 at 10:16:36AM +0800, Herbert Xu wrote: > 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 > > I think this is a fundamental bug in the kvmalloc non-blocking > support patch. How can it be used at all if it is susceptible > to such dead-locks? > > And if you can't use it safely why don't we just get rid of the > broken kvmalloc non-block path and have it always go to kmalloc > like it did before? > If we have a look at this as we did not have vmalloc() here: RTM_NEWNEIGH foo() or ... ============ ==================== lock_bh(&br->hash_lock) foo() lock(B) rhashtable_insert_rehash() foo() lock(B) waits for the other CPU softirq: a frame for the bridge lock(&br->hash_lock) waits for RTM_NEWNEIGH Same issue? I have a question: GFP_ATOMIC/GFP_NOWAIT guarantee they do not sleep. Do they guarantee not hitting ABBA dead-locks or they are not interrupted? -- Uladzislau Rezki