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([2620:10d:c092:600::1:b123]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cbe3963da88sm2563070a12.1.2026.08.02.05.44.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 02 Aug 2026 05:44:21 -0700 (PDT) Message-ID: <81e18535-e66a-498f-b293-3cb1c090fb9f@gmail.com> Date: Sun, 2 Aug 2026 13:44:11 +0100 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 v1 1/3] net: core: propagate unreadable flag in skb_zerocopy From: Pavel Begunkov To: Mina Almasry Cc: Stanislav Fomichev , Bobby Eshleman , Florian Westphal , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jason Xing , Kuniyuki Iwashima , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Jiayuan Chen , Willem de Bruijn , Kaiyuan Zhang , "open list:NETWORKING [GENERAL]" , open list References: <20260801125308.1342897-1-almasrymina@google.com> <11a640b6-46b1-44d6-aee6-872107f7f570@gmail.com> Content-Language: en-US In-Reply-To: <11a640b6-46b1-44d6-aee6-872107f7f570@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/2/26 13:33, Pavel Begunkov wrote: > On 8/1/26 13:52, Mina Almasry wrote: >> When skb_zerocopy() copies devmem payload fragments, it fails to update >> the target skb's unreadable flag. This causes the target to appear as >> readable memory. >> >> Propagate the unreadable flag if any devmem fragments were copied from >> the source. > > From a quick look, it doesn't seem like the function would work reliably > with netmems even with this patch, but that's a different kind of issue > we can return to later. Curious, did you hit this in prod? skb_shinfo(to)->nr_frags = j; + if (i > 0 && from->unreadable) + to->unreadable = 1; Taking another look, if j != i, it'd also have the mixing problem, and that can happen if it hits that head-to-frag copy. if (!skb_frags_readable(from) && j > 0 && len) // goto fault; Maybe add sth like this before the frag assignment loop? -- Pavel Begunkov