Re: rme9652: possible deadlock

[Abramo Bagnara <abramo.bagnara@libero.it>]

Jaroslav Kysela ha scritto:
> On Mon, 28 Apr 2003, Abramo Bagnara wrote:
> 
> 
>>Jeremy Hall ha scritto:
>>
>>>Will this fix allow both CPUs to run snd_pcm_period_elapsed() and friends 
>>>concurrently and then if XRUN is encountered grab the group lock, or will 
>>>one stream run at a time, in effect only allowing one card to process at a 
>>>time?
>>
>>As I've pointed to Jaroslav, current CVS code does not permit to both 
>>CPUs to run the interrupt handler of two linked streams concurrently.
>>
>>This is due to unconditional substitution of stream specific lock with a 
>>linked group lock.
>>
>>This is of course deadlock safe, but I think it's not the right solution.
> 
> 
> Sure, it was 1st version ;-)

Your missed answer to my objections made me suspected that ;-)

> It seems a bit complicated to me. We can do easy this block:
> 
> read_lock(link_manager);
> spin_lock(stream);
> ....
> if (stream_in_group)
>    spin_lock(group);
> ....
> if (stream_in_group)
>    spin_unlock(group);
> ....
> spin_unlock(stream);
> read_unlock(link_manager);
> 
> I cannot imagine any deadlock with this locking scheme, because stream 
> locks are independent now.

CPU1:

read_lock(link_manager);	read_lock(link_manager);
spin_lock(s1);			spin_lock(s2);
if (stream_in_group)		if (stream_in_group)
	spin_lock(group);		spin_lock(group); /* Waiting */
spin_lock(s2); /* BOOM! */

I guess that 3rd version will be the one I propose ;-)

(but probably the right one will be the forthcoming 4th)

-- 
Abramo Bagnara                       mailto:abramo.bagnara@libero.it

Opera Unica                          Phone: +39.546.656023
Via Emilia Interna, 140
48014 Castel Bolognese (RA) - Italy



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