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Tue, 09 Jun 2026 02:12:38 -0700 (PDT) Received: from [192.168.88.32] ([150.228.93.44]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-bf0553060dasm1006636266b.44.2026.06.09.02.12.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jun 2026 02:12:37 -0700 (PDT) Message-ID: <8bac773f-5016-4afb-8506-9d48eb2e70d0@redhat.com> Date: Tue, 9 Jun 2026 11:12:35 +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 v2] net: stmmac: xgmac2: disable RBUE in default RX interrupt mask To: Simon Horman , muhammad.nazim.amirul.nazle.asmade@altera.com Cc: netdev@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, rmk+kernel@armlinux.org.uk, maxime.chevallier@bootlin.com, Jose.Abreu@synopsys.com, linux-kernel@vger.kernel.org References: <20260604094512.21243-1-muhammad.nazim.amirul.nazle.asmade@altera.com> <20260608152717.157757-1-horms@kernel.org> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260608152717.157757-1-horms@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/8/26 5:27 PM, Simon Horman wrote: > From: 'Simon Horman' > > This is an AI-generated review of your patch. The human sending this > email has considered the AI review valid, or at least plausible. > Full review at: https://sashiko.dev > --- > net: stmmac: xgmac2: disable RBUE in default RX interrupt mask > > This commit removes the RX Buffer Unavailable (RBUE) interrupt from the > default enable masks for XGMAC2 devices. This is intended to prevent MAC > interrupt storms that can occur under heavy RX pressure when the DMA > runs out of RX descriptors. > >> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h >> index 51943705a2b03..b5fdc253a2f24 100644 >> --- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h >> +++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h >> @@ -379,9 +379,9 @@ >> #define XGMAC_RIE BIT(6) >> #define XGMAC_TBUE BIT(2) >> #define XGMAC_TIE BIT(0) >> -#define XGMAC_DMA_INT_DEFAULT_EN (XGMAC_NIE | XGMAC_AIE | XGMAC_RBUE | \ >> +#define XGMAC_DMA_INT_DEFAULT_EN (XGMAC_NIE | XGMAC_AIE | \ >> XGMAC_RIE | XGMAC_TIE) >> -#define XGMAC_DMA_INT_DEFAULT_RX (XGMAC_RBUE | XGMAC_RIE) >> +#define XGMAC_DMA_INT_DEFAULT_RX (XGMAC_RIE) > > [Severity: High] > Does removing the RBUE interrupt break the driver's ability to recover from > RX out-of-memory conditions, leading to a permanent RX queue stall? > > When stmmac_rx() processes packets, it calls stmmac_rx_refill() to replenish > the ring descriptors. If page_pool_alloc_pages() fails due to memory > pressure, the descriptors remain empty: > > drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:stmmac_rx_refill() { > ... > buf->page = page_pool_alloc_pages(rx_q->page_pool, gfp); > if (!buf->page) > break; > ... > } > > stmmac_rx() then returns the number of processed packets, which will be > less than the NAPI budget if the ring is empty. This causes > stmmac_napi_poll_rx() to complete NAPI and re-enable interrupts: > > drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:stmmac_napi_poll_rx() { > ... > work_done = stmmac_rx(priv, budget, chan); > if (work_done < budget && napi_complete_done(napi, work_done)) { > ... > stmmac_enable_dma_irq(priv, priv->ioaddr, chan, 1, 0); > } > ... > } > > When the hardware subsequently tries to receive a packet, it finds no > descriptors and enters the Receive Buffer Unavailable (RBU) state. By > removing XGMAC_RBUE from the RX interrupt enable mask, the MAC will no > longer trigger an interrupt for the RBU state. > > Because no packets can be successfully received without descriptors, the > normal Receive Interrupt (RIE) will also never fire. With NAPI stopped and > no interrupts firing, the driver has no polling timer to retry allocation, > which could result in a permanent stall of the RX queue. Nazim, you need at least to clarify in the commit message why this patch is safe. /P