svn commit: r204126 - head/sys/powerpc/booke

[Rafal Jaworowski]

On 2010-02-20, at 17:13, Nathan Whitehorn wrote:

> Author: nwhitehorn
> Date: Sat Feb 20 16:13:43 2010
> New Revision: 204126
> URL: http://svn.freebsd.org/changeset/base/204126
> 
> Log:
>  Merge r198724 to Book-E. casuword() non-atomically read the current value
>  of its argument before atomically replacing it, which could occasionally
>  return the wrong value on an SMP system. This resulted in user mutex
>  operations hanging when using threaded applications.

Have you got a particular test case when this was breaking, so I can test?

> Modified:
>  head/sys/powerpc/booke/copyinout.c
> 
> Modified: head/sys/powerpc/booke/copyinout.c
> ==============================================================================
> --- head/sys/powerpc/booke/copyinout.c	Sat Feb 20 16:12:37 2010	(r204125)
> +++ head/sys/powerpc/booke/copyinout.c	Sat Feb 20 16:13:43 2010	(r204126)
> @@ -295,8 +295,19 @@ casuword(volatile u_long *addr, u_long o
> 		return (EFAULT);
> 	}
> 
> -	val = *addr;
> -	(void) atomic_cmpset_32((volatile uint32_t *)addr, old, new);
> +	__asm __volatile (
> +		"1:\tlwarx %0, 0, %2\n\t"	/* load old value */
> +		"cmplw %3, %0\n\t"		/* compare */
> +		"bne 2f\n\t"			/* exit if not equal */
> +		"stwcx. %4, 0, %2\n\t"      	/* attempt to store */
> +		"bne- 1b\n\t"			/* spin if failed */
> +		"b 3f\n\t"			/* we've succeeded */
> +		"2:\n\t"
> +		"stwcx. %0, 0, %2\n\t"       	/* clear reservation (74xx) */

The 74xx comment reference is somewhat confusing as the clear reservation operation is pretty uniform accross 32-bit PowerPC I guess, and not 74xx specific.

Rafal