Re: [alsa-cvslog] CVS: alsa-kernel/core rawmidi.c,1.40,1.41

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

Jaroslav Kysela ha scritto:
> Modified Files:
> 	rawmidi.c 
> Log Message:
> copy_*_user() function cannot be called from spinlock context
> 
> Index: rawmidi.c
> ===================================================================
> RCS file: /cvsroot/alsa/alsa-kernel/core/rawmidi.c,v
> retrieving revision 1.40
> retrieving revision 1.41
> diff -u -r1.40 -r1.41
> --- rawmidi.c	23 Oct 2003 14:34:52 -0000	1.40
> +++ rawmidi.c	1 Feb 2004 16:34:28 -0000	1.41
> @@ -909,10 +909,11 @@
>  		if (kernel) {
>  			memcpy(buf + result, runtime->buffer + runtime->appl_ptr, count1);
>  		} else {
> +			spin_unlock_irqrestore(&runtime->lock, flags);
>  			if (copy_to_user(buf + result, runtime->buffer + runtime->appl_ptr, count1)) {
> -				spin_unlock_irqrestore(&runtime->lock, flags);
>  				return result > 0 ? result : -EFAULT;
>  			}
> +			spin_lock_irqsave(&runtime->lock, flags);
>  		}
>  		runtime->appl_ptr += count1;
>  		runtime->appl_ptr %= runtime->buffer_size;
> @@ -1133,10 +1134,13 @@
>  		if (kernel) {
>  			memcpy(runtime->buffer + runtime->appl_ptr, buf, count1);
>  		} else {
> +			spin_unlock_irqrestore(&runtime->lock, flags);
>  			if (copy_from_user(runtime->buffer + runtime->appl_ptr, buf, count1)) {
> +				spin_lock_irqsave(&runtime->lock, flags);
>  				result = result > 0 ? result : -EFAULT;
>  				goto __end;
>  			}
> +			spin_lock_irqsave(&runtime->lock, flags);
>  		}
>  		runtime->appl_ptr += count1;
>  		runtime->appl_ptr %= runtime->buffer_size;


With this patch you break write and read atomicity, you should:

1) read and save appl_ptr
2) update appl_ptr and avail
3) leave critical area
4) copy from/to user using saved appl_ptr
5) reenter critical area

I've just checked and a similar mistake has been done too for PCM (and 
other places?).


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

Opera Unica                          Phone: +39.0546.656023
Via Emilia Interna, 140
48014 Castel Bolognese (RA) - Italy


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