kern/78179: bus_dmamem_alloc() with BUS_DMA_NOWAIT can block

[Mark Tinguely]

The following reply was made to PR kern/78179; it has been noted by GNATS.

From: Mark Tinguely <tinguely at casselton.net>
To: bug-followup at FreeBSD.org, PeterJeremy at optushome.com.au
Cc:  
Subject: Re: kern/78179: bus_dmamem_alloc() with BUS_DMA_NOWAIT can block
Date: Thu, 11 May 2006 11:56:06 -0500 (CDT)

 I stated in the -current mailing list that my original patch to
 sys/vm/vm_contig.c was wrong. The following is closer to what should
 be done.
 
 --- vm_contig.c.orig	Fri Mar 10 14:30:07 2006
 +++ vm_contig.c	Thu May 11 11:50:14 2006
 @@ -86,7 +86,7 @@
  #include <vm/vm_extern.h>
  
  static int
 -vm_contig_launder_page(vm_page_t m)
 +vm_contig_launder_page(vm_page_t m, int flags)
  {
  	vm_object_t object;
  	vm_page_t m_tmp;
 @@ -96,6 +96,20 @@
  	object = m->object;
  	if (!VM_OBJECT_TRYLOCK(object))
  		return (EAGAIN);
 +
 +  	if (flags & M_NOWAIT) { /* cannot sleep in interrupt mode */
 + 		if ((m->flags & PG_BUSY) || m->busy) {
 +			VM_OBJECT_UNLOCK(object);
 + 			return (EBUSY);
 + 		} else {
 + 			vm_page_test_dirty(m);
 + 			if (m->dirty) {
 + 				VM_OBJECT_UNLOCK(object);
 + 				return (EAGAIN);
 + 			}
 + 		}
 + 	}
 +
  	if (vm_page_sleep_if_busy(m, TRUE, "vpctw0")) {
  		VM_OBJECT_UNLOCK(object);
  		vm_page_lock_queues();
 @@ -138,7 +152,7 @@
  }
  
  static int
 -vm_contig_launder(int queue)
 +vm_contig_launder(int queue, int flags)
  {
  	vm_page_t m, next;
  	int error;
 @@ -152,7 +166,7 @@
  
  		KASSERT(VM_PAGE_INQUEUE2(m, queue),
  		    ("vm_contig_launder: page %p's queue is not %d", m, queue));
 -		error = vm_contig_launder_page(m);
 +		error = vm_contig_launder_page(m, flags);
  		if (error == 0)
  			return (TRUE);
  		if (error == EBUSY)
 @@ -233,12 +247,12 @@
  				actmax = vm_page_queues[PQ_ACTIVE].lcnt;
  again1:
  				if (inactl < inactmax &&
 -				    vm_contig_launder(PQ_INACTIVE)) {
 +				    vm_contig_launder(PQ_INACTIVE, flags)) {
  					inactl++;
  					goto again1;
  				}
  				if (actl < actmax &&
 -				    vm_contig_launder(PQ_ACTIVE)) {
 +				    vm_contig_launder(PQ_ACTIVE, flags)) {
  					actl++;
  					goto again1;
  				}
 @@ -390,7 +404,7 @@
  
  vm_page_t
  vm_page_alloc_contig(vm_pindex_t npages, vm_paddr_t low, vm_paddr_t high,
 -	    vm_offset_t alignment, vm_offset_t boundary)
 +	    vm_offset_t alignment, vm_offset_t boundary, int flags)
  {
  	vm_object_t object;
  	vm_offset_t size;
 @@ -483,7 +497,7 @@
  			    pqtype != PQ_CACHE) {
  				if (m->queue == PQ_ACTIVE ||
  				    m->queue == PQ_INACTIVE) {
 -					if (vm_contig_launder_page(m) != 0)
 +					if (vm_contig_launder_page(m, flags) != 0)
  						goto cleanup_freed;
  					pqtype = m->queue - m->pc;
  					if (pqtype != PQ_FREE &&
 @@ -590,7 +604,7 @@
  		    boundary, kernel_map);
  	} else {
  		pages = vm_page_alloc_contig(npgs, low, high,
 -		    alignment, boundary);
 +		    alignment, boundary, flags);
  		if (pages == NULL) {
  			ret = NULL;
  		} else {