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[73.185.129.58]) by smtp.googlemail.com with ESMTPSA id w10sm1921603ioc.55.2021.08.13.19.25.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Aug 2021 19:25:24 -0700 (PDT) Subject: Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in ipa_start_xmit() To: Jakub Kicinski Cc: davem@davemloft.net, bjorn.andersson@linaro.org, evgreen@chromium.org, cpratapa@codeaurora.org, subashab@codeaurora.org, elder@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210812195035.2816276-1-elder@linaro.org> <20210812195035.2816276-5-elder@linaro.org> <20210813174655.1d13b524@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Alex Elder Message-ID: <3a9e82cc-c09e-62e8-4671-8f16d4f6a35b@linaro.org> Date: Fri, 13 Aug 2021 21:25:23 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210813174655.1d13b524@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/13/21 7:46 PM, Jakub Kicinski wrote: > On Thu, 12 Aug 2021 14:50:33 -0500 Alex Elder wrote: >> + /* The hardware must be powered for us to transmit */ >> + dev = &ipa->pdev->dev; >> + ret = pm_runtime_get(dev); >> + if (ret < 1) { >> + /* If a resume won't happen, just drop the packet */ >> + if (ret < 0 && ret != -EINPROGRESS) { >> + pm_runtime_put_noidle(dev); >> + goto err_drop_skb; >> + } > > This is racy, what if the pm work gets scheduled on another CPU and > calls wake right here (i.e. before you call netif_stop_queue())? > The queue may never get woken up? I haven't been seeing this happen but I think you may be right. I did think about this race, but I think I was relying on the PM work queue to somehow avoid the problem. I need to think about this again after a good night's sleep. I might need to add an atomic flag or something. -Alex >> + /* No power (yet). Stop the network stack from transmitting >> + * until we're resumed; ipa_modem_resume() arranges for the >> + * TX queue to be started again. >> + */ >> + netif_stop_queue(netdev); >> + >> + (void)pm_runtime_put(dev); >> + >> + return NETDEV_TX_BUSY;