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d="scan'208";a="719613457" Received: from aslawinx-mobl.ger.corp.intel.com (HELO [10.99.16.144]) ([10.99.16.144]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jul 2023 08:16:40 -0700 Message-ID: <9919760c-aaef-06ea-b97c-7a2781f63fb1@linux.intel.com> Date: Thu, 6 Jul 2023 17:16:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [bug report] ALSA: jack: Access input_dev under mutex Content-Language: en-US From: =?UTF-8?Q?Amadeusz_S=c5=82awi=c5=84ski?= To: Takashi Iwai , Dan Carpenter Cc: alsa-devel@alsa-project.org References: <87sfa42j76.wl-tiwai@suse.de> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Message-ID-Hash: P7OVPAIITMTVOJ5EDVDD3Z7SNSEVZFPJ X-Message-ID-Hash: P7OVPAIITMTVOJ5EDVDD3Z7SNSEVZFPJ X-MailFrom: amadeuszx.slawinski@linux.intel.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-alsa-devel.alsa-project.org-0; header-match-alsa-devel.alsa-project.org-1; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.8 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On 7/5/2023 4:47 PM, Amadeusz Sławiński wrote: > On 7/4/2023 10:07 AM, Takashi Iwai wrote: >> On Mon, 03 Jul 2023 16:18:27 +0200, >> Dan Carpenter wrote: >>> >>> Hello Amadeusz Sławiński, >>> >>> The patch 1b6a6fc5280e: "ALSA: jack: Access input_dev under mutex" >>> from Apr 12, 2022, leads to the following Smatch static checker >>> warning: >>> >>>     sound/core/jack.c:673 snd_jack_report() >>>     warn: sleeping in atomic context >>> >>> sound/core/jack.c >>>      663         jack->hw_status_cache = status; >>>      664 >>>      665         list_for_each_entry(jack_kctl, &jack->kctl_list, list) >>>      666                 if (jack_kctl->sw_inject_enable) >>>      667                         mask_bits |= jack_kctl->mask_bits; >>>      668                 else >>>      669                         snd_kctl_jack_report(jack->card, >>> jack_kctl->kctl, >>>      670                                              status & >>> jack_kctl->mask_bits); >>>      671 >>>      672 #ifdef CONFIG_SND_JACK_INPUT_DEV >>> --> 673         mutex_lock(&jack->input_dev_lock); >>>                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >>> >>> That patch adds this mutex but we can't take mutex because we're already >>> holding a spinlock.  The problematic call trees are: >>> >>> virtsnd_event_notify_cb() <- disables preempt >>> virtsnd_disable_event_vq() <- disables preempt >>> -> virtsnd_event_dispatch() >>>     -> virtsnd_jack_event() >>>        -> snd_jack_report() >>> >>> The virtsnd_event_notify_cb() and virtsnd_disable_event_vq() functions >>> take the spin_lock_irqsave(&queue->lock, flags); >> >> Indeed it was no good choice to use the mutex there inside the report >> function.  It's supposed to be callable from an irq-disabled context, >> too. >> >> How about simply using the device refcount like below? >> >> Although we may drop the mutex from snd_jack, it can can be left, as >> it's still useful for protecting a potential race between creation and >> deletion. >> >> >> thanks, >> >> Takashi >> >> -- 8< -- >> --- a/sound/core/jack.c >> +++ b/sound/core/jack.c >> @@ -654,6 +654,7 @@ void snd_jack_report(struct snd_jack *jack, int >> status) >>       struct snd_jack_kctl *jack_kctl; >>       unsigned int mask_bits = 0; >>   #ifdef CONFIG_SND_JACK_INPUT_DEV >> +    struct input_dev *idev; >>       int i; >>   #endif >> @@ -670,17 +671,15 @@ void snd_jack_report(struct snd_jack *jack, int >> status) >>                            status & jack_kctl->mask_bits); >>   #ifdef CONFIG_SND_JACK_INPUT_DEV >> -    mutex_lock(&jack->input_dev_lock); >> -    if (!jack->input_dev) { >> -        mutex_unlock(&jack->input_dev_lock); >> +    idev = input_get_device(jack->input_dev); >> +    if (!idev) >>           return; >> -    } >>       for (i = 0; i < ARRAY_SIZE(jack->key); i++) { >>           int testbit = ((SND_JACK_BTN_0 >> i) & ~mask_bits); >>           if (jack->type & testbit) >> -            input_report_key(jack->input_dev, jack->key[i], >> +            input_report_key(idev, jack->key[i], >>                        status & testbit); >>       } >> @@ -688,13 +687,13 @@ void snd_jack_report(struct snd_jack *jack, int >> status) >>           int testbit = ((1 << i) & ~mask_bits); >>           if (jack->type & testbit) >> -            input_report_switch(jack->input_dev, >> +            input_report_switch(idev, >>                           jack_switch_types[i], >>                           status & testbit); >>       } >> -    input_sync(jack->input_dev); >> -    mutex_unlock(&jack->input_dev_lock); >> +    input_sync(idev); >> +    input_put_device(idev); >>   #endif /* CONFIG_SND_JACK_INPUT_DEV */ >>   } >>   EXPORT_SYMBOL(snd_jack_report); > > > Looking at code it looks like it should also work. Will schedule test > run tomorrow to see if it causes any problems. I've run tests and see nothing worrying, so Tested-by: Amadeusz Sławiński