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Thu, 05 Nov 2026 10:44:32 -0800 (PST) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c4d354ac249sm8993666b.5.2026.11.05.10.44.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 10:44:32 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 5 Nov 2026 19:44:30 +0100 To: Herbert Xu Cc: Uladzislau Rezki , Linus Torvalds , "Liam R. Howlett (Google)" , Davidlohr Bueso , 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Nov 05, 2026 at 04:51:39PM +0800, Herbert Xu wrote: > On Wed, Nov 04, 2026 at 12:11:24PM +0100, Uladzislau Rezki wrote: > > > > There are users in kernel. For example: > > Thanks for the list. > > > 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); > > These appear to be executing out of process context without spin > locks so they're not really GFP_ATOMIC. > > > Virtio ring-testing: > > (alloc_ring(0)), gfpflags_allow_blocking(0) does not allow blocking. > > I didn't really look into this as it's just test code. > > > net/ipv4/udp.c: > > err = bpf_iter_udp_realloc_batch(iter, batch_sks, GFP_NOWAIT); > > This looks buggy in exactly the same way as rhashtable. It's > called under spin_lock_bh, and the same lock can be taken on > the softirq path on another CPU. > > So are there any safe users of kvmalloc with GFP_ATOMIC? If not > I suggest that we change kvmalloc to disallow vmalloc when called > with GFP_ATOMIC. > kvmalloc() disallow and vmalloc() allow? The deadlock looks like from below spin_lock(): diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c index e4570bbed854..97aac4a4a92b 100644 --- a/net/bridge/br_fdb.c +++ b/net/bridge/br_fdb.c @@ -1025,7 +1025,13 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source, } } } else { - spin_lock(&br->hash_lock); + if (in_serving_softirq()) { + if (!spin_trylock(&br->hash_lock)) + return; + } else { + spin_lock(&br->hash_lock); + } + fdb = fdb_create(br, source, addr, vid, flags); if (fdb) { trace_br_fdb_update(br, source, addr, vid, flags); is that applicable for bridge update code? -- Uladzislau Rezki