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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Qingfang Deng , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next] net: dev_addr_lists: don't WARN on GFP_ATOMIC kmalloc failure in netif_rx_mode_run In-Reply-To: <20260519095557.3749407-1-yzjaurora@gmail.com> (Zijing Yin's message of "Tue, 19 May 2026 02:55:55 -0700") References: <20260519095557.3749407-1-yzjaurora@gmail.com> Date: Tue, 19 May 2026 13:22:33 +0200 Message-ID: <878q9fod8m.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain 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.