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Wed, 04 Nov 2026 03:11:26 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 4 Nov 2026 12:11:24 +0100 To: Herbert Xu Cc: Linus Torvalds , "Liam R. Howlett (Google)" , Davidlohr Bueso , 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: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: tar85ywch95r19f3mauhwnorjnuu3wrm X-Rspamd-Queue-Id: 96B63C0002 X-Rspam-User: X-Rspamd-Server: rspam08 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-HE-Tag: 1793790688-370130 X-HE-Meta: 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 v2AI7lqA 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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 Hello, Herbert! > > > > None of that says why. It only repeats what I already said: it seems > > to be due to kmsan doing bad things. > > Fair enough. > > When I was told that folks needed vmalloc under GFP_ATOMIC I didn't > question it any further: > > https://lore.kernel.org/all/aeiHkG7X_dieMdw5@milan/ > > Looking back, it does look like it was never explained who these > folks are. > > Ulazislau, so who needs vmalloc GFP_ATOMIC support in the kernel? > Or is it only used by out-of-kernel code? > There are users in kernel. For example: drivers/GPU /* Allocate the file in vmalloc memory, it's likely to be big */ iter.start = __vmalloc(file_size, GFP_NOWAIT); AMD-GPU: kvzalloc(size, GFP_NOWAIT); kvzalloc_objs(struct amdgpu_coredump_ring, GFP_NOWAIT); kvzalloc(ring->ring_size, GFP_NOWAIT); Virtio ring-testing: (alloc_ring(0)), gfpflags_allow_blocking(0) does not allow blocking. net/ipv4/udp.c: err = bpf_iter_udp_realloc_batch(iter, batch_sks, GFP_NOWAIT); etc... Apart of above, the obvious user of GFP_ATOMIC is the bridge forwarding database. The br_fdb_add_local() holds br->hash_lock with bottom halves disabled, on rehash event it invokes rhashtable_insert_rehash() to allocate a new bucket table with GFP_ATOMIC | __GFP_NOWARN. In that scenario kvmalloc() can fallback to vmalloc(). This path runs and exists because syzbot hit the old in_interrupt() check there, leading to 04aa71da5f3 ("mm/vmalloc: do not trigger BUG() on BH disabled context"). The vmalloc() fallback improves the chance of completing the insert on the spot to minimize -ENOMEM hit rate thus minimize queuing the irq_work_queue(&ht->run_irq_work) to retry allocation in process context. According to XFS code and comments it wants non-blocking support for kvmalloc(). But indeed the v4 cover letter didn't name a consumer. The bridge report came later. -- Uladzislau Rezki