svn commit: r216944 - head/sys/i386/xen

[John Baldwin]

On Monday, January 03, 2011 7:16:38 pm Colin Percival wrote:
> Author: cperciva
> Date: Tue Jan  4 00:16:38 2011
> New Revision: 216944
> URL: http://svn.freebsd.org/changeset/base/216944
> 
> Log:
>   Adjust the critical section protecting _xen_flush_queue to cover the
>   entire range where the page mapping request queue needs to be atomically
>   examined and modified.
>   
>   Oddly, while this doesn't seem to affect the overall rate of panics
>   (running 'make index' on EC2 t1.micro instances, there are 0.6 +/- 0.1
>   panics per hour, both before and after this change), it eliminates
>   vm_fault from panic backtraces, leaving only backtraces going through
>   vmspace_fork.
> 
> Modified:
>   head/sys/i386/xen/xen_machdep.c
> 
> Modified: head/sys/i386/xen/xen_machdep.c
> 
==============================================================================
> --- head/sys/i386/xen/xen_machdep.c	Tue Jan  4 00:11:09 2011	(r216943)
> +++ head/sys/i386/xen/xen_machdep.c	Tue Jan  4 00:16:38 2011	(r216944)
> @@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
>  #include <sys/malloc.h>
>  #include <sys/mutex.h>
>  #include <sys/kernel.h>
> +#include <sys/proc.h>
>  #include <sys/reboot.h>
>  #include <sys/sysproto.h>
>  
> @@ -249,10 +250,13 @@ _xen_flush_queue(void)
>  	SET_VCPU();
>  	int _xpq_idx = XPQ_IDX;
>  	int error, i;
> -	/* window of vulnerability here? */
>  
> +#ifdef INVARIANTS
>  	if (__predict_true(gdtset))
> -		critical_enter();
> +		KASSERT(curthread->td_critnest > 0,
> +		    ("xen queue flush should be in a critical section"));
> +#endif
> +

You can use CRITICAL_ASSERT(curthread) instead perhaps.

>  	XPQ_IDX = 0;
>  	/* Make sure index is cleared first to avoid double updates. */
>  	error = HYPERVISOR_mmu_update((mmu_update_t *)&XPQ_QUEUE,
> @@ -286,8 +290,6 @@ _xen_flush_queue(void)
>  		}
>  	}
>  #endif	
> -	if (__predict_true(gdtset))
> -		critical_exit();
>  	if (__predict_false(error < 0)) {
>  		for (i = 0; i < _xpq_idx; i++)
>  			printf("val: %llx ptr: %llx\n",
> @@ -301,7 +303,12 @@ void
>  xen_flush_queue(void)
>  {
>  	SET_VCPU();
> +
> +	if (__predict_true(gdtset))
> +		critical_enter();
>  	if (XPQ_IDX != 0) _xen_flush_queue();
> +	if (__predict_true(gdtset))
> +		critical_exit();
>  }
>  
>  static __inline void
> 

-- 
John Baldwin