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[67.180.167.114]) by smtp.gmail.com with ESMTPSA id m25-v6sm1354332pfg.61.2018.06.25.23.44.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Jun 2018 23:44:23 -0700 (PDT) Subject: Re: [PATCH] NFC: llcp: fix nfc_llcp_send_ui_frame() lockup To: Sergey Senozhatsky , Dmitry Vyukov Cc: Samuel Ortiz , "David S. Miller" , Steven Rostedt , Petr Mladek , syzkaller-bugs , linux-wireless@vger.kernel.org, netdev , LKML , syzbot , Sergey Senozhatsky References: <20180626044119.30118-1-sergey.senozhatsky@gmail.com> <20180626051221.GC31439@jagdpanzerIV> From: Eric Dumazet Message-ID: <8c410102-43ab-dfdb-0d71-2ee5951e1af8@gmail.com> Date: Mon, 25 Jun 2018 23:44:22 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180626051221.GC31439@jagdpanzerIV> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/25/2018 10:12 PM, Sergey Senozhatsky wrote: > On (06/26/18 07:07), Dmitry Vyukov wrote: > [..] >>> #include >>> @@ -755,7 +756,8 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap, >>> pdu = nfc_alloc_send_skb(sock->dev, &sock->sk, MSG_DONTWAIT, >>> frag_len + LLCP_HEADER_SIZE, &err); >>> if (pdu == NULL) { >>> - pr_err("Could not allocate PDU\n"); >>> + pr_err_ratelimited("Could not allocate PDU\n"); >>> + cond_resched(); >>> continue; >>> } >> >> >> But this thread is still in an infinite (unkillable?) loop? If yes, we >> are waiting for the next syzbot report ;) > > The loop is still infinite, correct, but we have a preemption point now. > Sure, net people can come with a much better solution, I'll be happy to > scratch my patch. > This can not be the right solution, think about current thread being real time, cond_resched() might be a nop. We should probably not loop at all, or not use MSG_DONTWAIT. (And remove this useless "Could not allocate PDU" message) NFC maintainers should really take a look at this.