linux-kernel - Re: [PATCH V0 1/1] ALSA: pcm: fix blocking while loop in snd_pcm_update_hw

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Message-ID: <s5hee3nrnix.wl-tiwai@suse.de>
Date:   Mon, 28 Feb 2022 16:58:30 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Raghu Ballappa Bankapur <quic_rbankapu@...cinc.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Vinod Koul <vkoul@...nel.org>,
        Takashi Iwai <tiwai@...e.com>,
        "ierre-Louis Bossart" <pierre-louis.bossart@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        "Ranjani Sridharan" <ranjani.sridharan@...ux.intel.com>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        <alsa-devel@...a-project.org>, Zubin Mithra <zsm@...omium.org>,
        <linux-kernel@...r.kernel.org>,
        Krishna Jha <quic_kkishorj@...cinc.com>
Subject: Re: [PATCH V0 1/1] ALSA: pcm: fix blocking while loop in snd_pcm_update_hw_ptr0()

On Fri, 25 Feb 2022 13:26:36 +0100,
Raghu Ballappa Bankapur wrote:
> 
> Hi Takashi,
> 
> Thanks for your feedback.
> 
> I see your below statement
> 
> But, having either this zero check or minimal hw_ptr_buffer_jiffies=1
> would be good in anyway, even if we add more check for the hw_params
> for no-period-wakeup case.
> 
> Please review if those changes are Ok

If you mean about your posted patch for "those changes", as Jaroslav
suggested in the thread, we may take a different approach: just set
the minimal hw_ptr_buffer_jiffies to 1.

Could you try this and submit the fix if that works for you?


thanks,

Takashi

> 
> Regards
> Raghu
> 
> On 2/25/2022 4:53 PM, Takashi Iwai wrote:
> 
>     On Fri, 25 Feb 2022 11:52:05 +0100,
>     Jaroslav Kysela wrote:
>     
>         On 25. 02. 22 11:39, Raghu Bankapur wrote:
>         
>             When period interrupts are disabled, while loop in snd_pcm_update_hw_ptr0()
>             results in the machine locking up if runtime->hw_ptr_buffer_jiffies is 0.
>             Validate runtime->hw_ptr_buffer_jiffies value before while loop to avoid
>             delta check.
>             
>         I would set hw_ptr_buffer_jiffies to 1 in this case in snd_pcm_post_start().
>         
>     I thought of it at the first glance, but after reading the code again,
>     I doubt whether it makes sense at all to allow this condition.
>     Since the buffer size is too small and the rate is too high, we can't
>     calculate the buffer crossing condition accurately under such
>     condition.
>     
>     But, having either this zero check or minimal hw_ptr_buffer_jiffies=1
>     would be good in anyway, even if we add more check for the hw_params
>     for no-period-wakeup case.
> 
>     thanks,
>     
>     Takashi
> 
>