From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alan Young <Alan.Young@IEE.org>
Subject: Re: Locking/mutex for snd_pcm_update_hw_ptr0() call
Date: Mon, 7 Nov 2016 14:56:00 +0000
Message-ID: <58209600.1090908@IEE.org>
References: <58207934.8080006@IEE.org>
 <6a229803-cfe2-81b0-d873-902831e3314d@ladisch.de>
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To: Clemens Ladisch <clemens@ladisch.de>, alsa-devel@alsa-project.org
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On 07/11/16 14:15, Clemens Ladisch wrote:
> Alan Young wrote:
>> It is possible that the DMA interrupt handler could call
>> snd_pcm_update_hw_ptr0() while it is part way through a call
>> from snd_pcm_status(), or vice versa?
> The *lock_irq* functions disable interrupts on the current CPU.
>
>

But only on the current CPU? So that would imply that multiple threads 
could execute snd_pcm_update_hw_ptr0() simultaneously on multi-CPU systems.

Even on a single-CPU system, I presume that the interrupt handler cannot 
be pre-empted by a user-space call such as snd_pcm_status(). Is that 
correct?

Alan.