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Thu, 14 May 2026 05:01:22 -0700 (PDT) X-Received: by 2002:a05:600c:19ce:b0:48e:7f1c:8778 with SMTP id 5b1f17b1804b1-48fc9a34577mr102347405e9.17.1778760082064; Thu, 14 May 2026 05:01:22 -0700 (PDT) Received: from [192.168.88.32] ([216.128.9.106]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48fd64cebaasm59995375e9.11.2026.05.14.05.01.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 May 2026 05:01:21 -0700 (PDT) Message-ID: <4ca19ae1-6606-433b-9860-0a8cce12f80f@redhat.com> Date: Thu, 14 May 2026 14:01:20 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net/stmmac: Fix free-after-use panic when interface goes does with XDP To: Jakub Raczynski , netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com, k.domagalski@samsung.com, k.tegowski@samsung.com, Chang-Sub Lee References: <20260511165045.3091475-1-j.raczynski@samsung.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260511165045.3091475-1-j.raczynski@samsung.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/11/26 6:50 PM, Jakub Raczynski wrote: > When running XDP forwarding and interface gets shut down, kernel might panic > or show SLUB "poison overwritten" errors due to a race condition between > NAPI polling and resource freeing. > > Observed error is one of following: > - Poison overwrriten > [ 1889.547746] eth1: Link is Down > [ 1889.549940] ============================================================================= > [ 1889.549954] BUG kmalloc-4k (Tainted: G B ): Poison overwritten > [ 1889.549959] ----------------------------------------------------------------------------- > [ 1889.549963] 0xffffff882dcc4d80-0xffffff882dcc4da7 @offset=19840. First byte 0x0 instead of 0x6b > [ 1889.549969] Allocated in __alloc_dma_tx_desc_resources+0x60/0x10c [stmmac] age=169 cpu=7 pid=27759 > [ 1889.550020] __kmem_cache_alloc_node+0x100/0x2e8 > [ 1889.550032] __kmalloc+0x58/0x1a0 > [ 1889.550039] __alloc_dma_tx_desc_resources+0x60/0x10c [stmmac] > [ 1889.550052] alloc_dma_desc_resources+0xec/0x164 [stmmac] > [ 1889.550064] stmmac_setup_dma_desc+0xec/0x1e4 [stmmac] > [ 1889.550076] stmmac_open+0x28/0x94 [stmmac] > [...] > > - Wrong memory address > [ 1901.546692] Unable to handle kernel paging request at virtual address dead000000000122 > [...] > [ 1902.964068] Call trace: > [ 1902.967193] free_to_partial_list+0x560/0x600 > [ 1902.972227] __slab_free+0x1a8/0x420 > [ 1902.976480] __kmem_cache_free+0x204/0x218 > [ 1902.981254] kfree+0x6c/0x128 > [ 1902.984900] kvfree+0x3c/0x4c > [ 1902.988545] page_pool_release+0x234/0x27c > [ 1902.993320] page_pool_destroy+0xcc/0x190 > [ 1902.998006] __free_dma_rx_desc_resources+0x100/0x360 [stmmac] > [ 1903.004516] free_dma_desc_resources+0x8c/0xac [stmmac] > [ 1903.010419] stmmac_release+0x1c0/0x2b4 [stmmac] > [...] > > Root cause is stmmac_release() stops DMA and frees TX/RX ring buffers and > page pools while NAPI/XDP could still be accessing these resources in the > background. > > Fix this by following: > - Set STMMAC_DOWN flag before stopping DMA to signal XDP to stop > - Call synchronize_rcu() after stopping DMA but before freeing resources to > ensure all ongoing NAPI operations complete > - Add STMMAC_DOWN flag checks in XDP code paths (XDP_TX and XDP_REDIRECT) to > drop packets when interface is going down. This has already been done for > stmmac_xdp_xmit() so make it consistent > - Clear STMMAC_DOWN flag in __stmmac_open() to restore normal operation. > This was only done for stmmac_reset_subtask() during abnormal operation, > which is not enough. This does not affect normal operation as this flag is > used only for XDP apps The above looks racy. I think instead you should just use napi_synchronize() in __stmmac_release. > @@ -5267,6 +5279,9 @@ static int stmmac_xdp_xmit_back(struct stmmac_priv *priv, > if (unlikely(!xdpf)) > return STMMAC_XDP_CONSUMED; > > + if (unlikely(test_bit(STMMAC_DOWN, &priv->state))) > + return -ENETDOWN; Sashiko noted here you should return STMMAC_XDP_CONSUMED /P