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[73.185.129.58]) by smtp.googlemail.com with ESMTPSA id z26sm1603739iol.6.2021.08.16.10.56.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Aug 2021 10:56:41 -0700 (PDT) Subject: Re: [PATCH net-next 4/6] net: ipa: ensure hardware has power in ipa_start_xmit() From: Alex Elder 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> Message-ID: Date: Mon, 16 Aug 2021 12:56:40 -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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/16/21 9:20 AM, Alex Elder wrote: > 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. I'm finding this isn't an easy problem to solve (or even think about). While I ponder the best course of action I'm going to send out another series (i.e., *before* I send a fix for this issue) because I'd like to get everything I have out for review this week. I *will* address this potential race one way or another, possibly later today. -Alex > >                     -Alex >