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[73.185.129.58]) by smtp.googlemail.com with ESMTPSA id m26sm3210997ioj.54.2021.08.16.07.20.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Aug 2021 07:20:41 -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> <3a9e82cc-c09e-62e8-4671-8f16d4f6a35b@linaro.org> <20210816071543.39a44815@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Alex Elder Message-ID: Date: Mon, 16 Aug 2021 09:20:40 -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: <20210816071543.39a44815@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/16/21 9:15 AM, Jakub Kicinski wrote: > On Fri, 13 Aug 2021 21:25:23 -0500 Alex Elder wrote: >>> 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. > > Maybe add a spin lock? Seems like the whole wake up path will be > expensive enough for a spin lock to be in the noise. You can always > add complexity later. Exactly what I just decided after trying to work out a clever way without using a spinlock... I'll be sending out a fix today. Thanks. -Alex