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([2a02:aa16:1105:8100:aca5:18d3:d87:7987]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48fe5cab7c5sm344268795e9.12.2026.05.19.05.26.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 May 2026 05:26:56 -0700 (PDT) Message-ID: <8f25efa5-bd29-49d5-a260-e0ed0ab9ea75@gmail.com> Date: Tue, 19 May 2026 14:26:55 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next] net: dev_addr_lists: don't WARN on GFP_ATOMIC kmalloc failure in netif_rx_mode_run To: Jiayuan Chen Cc: Jakub Sitnicki , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Qingfang Deng , netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260519095557.3749407-1-yzjaurora@gmail.com> <878q9fod8m.fsf@cloudflare.com> Content-Language: en-US From: Zijing yin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Thanks! I will attach it accordingly. On 19.05.2026 14:22, Jiayuan Chen wrote: > On Tue, May 19, 2026 at 02:11:53PM +0800, Zijing yin wrote: >> Thank you so much for the feedback! I will address these comments in the >> next version. This is not found by syzbot by the way. > > There has the a syzbot report now: > https://syzkaller.appspot.com/bug?extid=f2421634072a4b47071e > >> >> Hope you have a great day! >> >> On 19.05.2026 13:22, Jakub Sitnicki wrote: >>> On Tue, May 19, 2026 at 02:55 AM -07, Zijing Yin wrote: >>>> netif_rx_mode_run() fires netdev_WARN() when netif_addr_lists_snapshot() >>>> returns non-zero. The only path to a non-zero return is -ENOMEM from >>>> __hw_addr_create() failing its kmalloc(GFP_ATOMIC) -- syzkaller hits it >>>> via failslab, and it can also be reached under real memory pressure. >>>> >>>> This is the only allocator-failure site in this file that WARNs. >>>> __hw_addr_create() itself, and every other caller of it in this file >>>> (__hw_addr_add_ex(), dev_uc_add_excl(), dev_uc_add(), dev_mc_add(), ...) >>>> just propagate the -ENOMEM silently. GFP_ATOMIC is a may-fail allocator; >>>> callers are required to handle NULL, so a returned -ENOMEM here is an >>>> expected runtime condition, not an invariant violation. >>>> >>>> The miss is self-healing: any subsequent change to dev->uc / dev->mc >>>> (every dev_{uc,mc}_{add,del}, IFF_PROMISC flip, etc.) calls >>>> __dev_set_rx_mode() -> netif_rx_mode_queue(), which re-queues the device >>>> and retries the sync. The only cost of a failed attempt is one stale >>>> rx-mode window until the next update; nothing in the kernel relies on >>>> this attempt succeeding. >>>> >>>> Demote to net_err_ratelimited() so the condition stays observable in >>>> dmesg without tripping panic_on_warn. >>>> >>>> Reproducer (syzkaller .prog format with setup notes): >>>> https://pastebin.com/t7AQKx9v >>>> >>>> Fixes: 3554b4345d85 ("net: introduce ndo_set_rx_mode_async and netdev_rx_mode_work") >>>> Signed-off-by: Zijing Yin >>>> --- >>>> net/core/dev_addr_lists.c | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c >>>> index d73fcb0c6..c6fdcac74 100644 >>>> --- a/net/core/dev_addr_lists.c >>>> +++ b/net/core/dev_addr_lists.c >>>> @@ -1275,7 +1275,8 @@ static void netif_rx_mode_run(struct net_device *dev) >>>> err = netif_addr_lists_snapshot(dev, &uc_snap, &mc_snap, >>>> &uc_ref, &mc_ref); >>>> if (err) { >>>> - netdev_WARN(dev, "failed to sync uc/mc addresses\n"); >>>> + net_err_ratelimited("%s: failed to sync uc/mc addresses\n", >>>> + netdev_name(dev)); >>>> netif_addr_unlock_bh(dev); >>>> return; >>>> } >>> >>> 1) I'd go with net_warn_ratelimited() instead. The promoted message >>> level in syslog might cause operational pain, and as you say the >>> condition is self-healing. Seems unwarranted. >>> >>> 2) Since it has a Fixes tag, should probably be sumitted for 'net' tree. >>> >>> 3) Was this reported by syzbot? If so, there should also be Reported-by >>> and Closes tags. >>