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([2402:f000:1:1501:200:5efe:a66f:8b73]) by smtp.gmail.com with ESMTPSA id c22sm12668511pfo.50.2020.01.13.00.20.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Jan 2020 00:20:35 -0800 (PST) Subject: Re: [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt() To: Takashi Iwai Cc: perex@perex.cz, tiwai@suse.com, rfontana@redhat.com, tglx@linutronix.de, allison@lohutok.net, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org References: <20200111163027.27135-1-baijiaju1990@gmail.com> From: Jia-Ju Bai Message-ID: Date: Mon, 13 Jan 2020 16:20:37 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/1/12 16:20, Takashi Iwai wrote: > On Sat, 11 Jan 2020 17:30:27 +0100, > Jia-Ju Bai wrote: >> The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger() >> may be concurrently executed. >> >> The function snd_cmipci_capture_trigger() calls >> snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable >> rec->running is written with holding a spinlock cm->reg_lock. But in >> snd_cmipci_interrupt(), the identical variable cm->channel[0].running >> or cm->channel[1].running is read without holding this spinlock. Thus, >> a possible data race may occur. >> >> To fix this data race, in snd_cmipci_interrupt(), the variables >> cm->channel[0].running and cm->channel[1].running are read with holding >> the spinlock cm->reg_lock. >> >> This data race is found by the runtime testing of our tool DILP-2. >> >> Signed-off-by: Jia-Ju Bai > Thanks for the patch. > > That's indeed a kind of race, but this change won't fix anything in > practice, though. The inconsistent running flag between those places, > there are two cases: > > - running became 0 to 1; this cannot happen, as the irq isn't issued > before the stream gets started > > - running became 1 to 0; this means that the stream gets stopped > between two points, and it's not better to call > snd_pcm_period_elapsed() for an already stopped stream. Thanks for the reply :) I am not sure to understand your words. Do you mean that this code should be also protected by the spinlock?     if (cm->pcm) {         if ((status & CM_CHINT0) && cm->channel[0].running)             snd_pcm_period_elapsed(cm->channel[0].substream);         if ((status & CM_CHINT1) && cm->channel[1].running)             snd_pcm_period_elapsed(cm->channel[1].substream);     } Best wishes, Jia-Ju Bai