[patch] i386 pmap sysmaps_pcpu[] atomic access

[Konstantin Belousov]

On Mon, Feb 18, 2013 at 01:44:35PM +0100, Svatopluk Kraus wrote:
> Hi,
> 
>    the access to sysmaps_pcpu[] should be atomic with respect to
> thread migration. Otherwise, a sysmaps for one CPU can be stolen by
> another CPU and the purpose of per CPU sysmaps is broken. A patch is
> enclosed.
And, what are the problem caused by the 'otherwise' ?
I do not see any.

Really, taking the mutex while bind to a CPU could be deadlock-prone
under some situations.

This was discussed at least one more time. Might be, a comment saying that
there is no issue should be added.
> 
>      Svata
> 
> Index: sys/i386/i386/pmap.c
> ===================================================================
> --- sys/i386/i386/pmap.c	(revision 246831)
> +++ sys/i386/i386/pmap.c	(working copy)
> @@ -4146,11 +4146,11 @@
>  {
>  	struct sysmaps *sysmaps;
> 
> +	sched_pin();
>  	sysmaps = &sysmaps_pcpu[PCPU_GET(cpuid)];
>  	mtx_lock(&sysmaps->lock);
>  	if (*sysmaps->CMAP2)
>  		panic("pmap_zero_page: CMAP2 busy");
> -	sched_pin();
>  	*sysmaps->CMAP2 = PG_V | PG_RW | VM_PAGE_TO_PHYS(m) | PG_A | PG_M |
>  	    pmap_cache_bits(m->md.pat_mode, 0);
>  	invlcaddr(sysmaps->CADDR2);
> @@ -4171,11 +4171,11 @@
>  {
>  	struct sysmaps *sysmaps;
> 
> +	sched_pin();
>  	sysmaps = &sysmaps_pcpu[PCPU_GET(cpuid)];
>  	mtx_lock(&sysmaps->lock);
>  	if (*sysmaps->CMAP2)
>  		panic("pmap_zero_page_area: CMAP2 busy");
> -	sched_pin();
>  	*sysmaps->CMAP2 = PG_V | PG_RW | VM_PAGE_TO_PHYS(m) | PG_A | PG_M |
>  	    pmap_cache_bits(m->md.pat_mode, 0);
>  	invlcaddr(sysmaps->CADDR2);
> @@ -4220,13 +4220,13 @@
>  {
>  	struct sysmaps *sysmaps;
> 
> +	sched_pin();
>  	sysmaps = &sysmaps_pcpu[PCPU_GET(cpuid)];
>  	mtx_lock(&sysmaps->lock);
>  	if (*sysmaps->CMAP1)
>  		panic("pmap_copy_page: CMAP1 busy");
>  	if (*sysmaps->CMAP2)
>  		panic("pmap_copy_page: CMAP2 busy");
> -	sched_pin();
>  	invlpg((u_int)sysmaps->CADDR1);
>  	invlpg((u_int)sysmaps->CADDR2);
>  	*sysmaps->CMAP1 = PG_V | VM_PAGE_TO_PHYS(src) | PG_A |
> @@ -5072,11 +5072,11 @@
>  	vm_offset_t sva, eva;
> 
>  	if ((cpu_feature & CPUID_CLFSH) != 0) {
> +		sched_pin();
>  		sysmaps = &sysmaps_pcpu[PCPU_GET(cpuid)];
>  		mtx_lock(&sysmaps->lock);
>  		if (*sysmaps->CMAP2)
>  			panic("pmap_flush_page: CMAP2 busy");
> -		sched_pin();
>  		*sysmaps->CMAP2 = PG_V | PG_RW | VM_PAGE_TO_PHYS(m) |
>  		    PG_A | PG_M | pmap_cache_bits(m->md.pat_mode, 0);
>  		invlcaddr(sysmaps->CADDR2);
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