kern/153672: commit references a PR

[dfilter service]

The following reply was made to PR kern/153672; it has been noted by GNATS.

From: dfilter at FreeBSD.ORG (dfilter service)
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/153672: commit references a PR
Date: Tue,  4 Jan 2011 15:55:21 +0000 (UTC)

 Author: cperciva
 Date: Tue Jan  4 15:55:15 2011
 New Revision: 216960
 URL: http://svn.freebsd.org/changeset/base/216960
 
 Log:
   Add hamfisted locking to the Xen/PV pmap code: Only allow one thread to
   be in {pmap_pinit, pmap_copy, pmap_release} at a time.
   
   This reduces the rate of panics when running 'make index' from ~0.6/hour
   to ~0.02/hour (p < 10^-30).
   
   At a later date this locking will be removed, and for this reason, it is
   wrapped in #ifdef HAMFISTED_LOCKING; this temporary hack is being put in
   place with the intention of shipping somewhat-stable Xen bits in FreeBSD
   8.2-RELEASE.
   
   PR:		kern/153672
   MFC after:	3 days
 
 Modified:
   head/sys/i386/xen/pmap.c
 
 Modified: head/sys/i386/xen/pmap.c
 ==============================================================================
 --- head/sys/i386/xen/pmap.c	Tue Jan  4 15:53:38 2011	(r216959)
 +++ head/sys/i386/xen/pmap.c	Tue Jan  4 15:55:15 2011	(r216960)
 @@ -202,6 +202,11 @@ __FBSDID("$FreeBSD$");
  
  #define pmap_pte_set_prot(pte, v) ((*(int *)pte &= ~PG_PROT), (*(int *)pte |= (v)))
  
 +#define HAMFISTED_LOCKING
 +#ifdef HAMFISTED_LOCKING
 +static struct mtx createdelete_lock;
 +#endif
 +
  struct pmap kernel_pmap_store;
  LIST_HEAD(pmaplist, pmap);
  static struct pmaplist allpmaps;
 @@ -502,6 +507,10 @@ pmap_bootstrap(vm_paddr_t firstaddr)
  	/* Turn on PG_G on kernel page(s) */
  	pmap_set_pg();
  #endif
 +
 +#ifdef HAMFISTED_LOCKING
 +	mtx_init(&createdelete_lock, "pmap create/delete", NULL, MTX_DEF);
 +#endif
  }
  
  /*
 @@ -1462,6 +1471,10 @@ pmap_pinit(pmap_t pmap)
  	static int color;
  	int i;
  
 +#ifdef HAMFISTED_LOCKING
 +	mtx_lock(&createdelete_lock);
 +#endif
 +
  	PMAP_LOCK_INIT(pmap);
  
  	/*
 @@ -1473,6 +1486,9 @@ pmap_pinit(pmap_t pmap)
  		    NBPTD);
  		if (pmap->pm_pdir == NULL) {
  			PMAP_LOCK_DESTROY(pmap);
 +#ifdef HAMFISTED_LOCKING
 +			mtx_unlock(&createdelete_lock);
 +#endif
  			return (0);
  		}
  #ifdef PAE
 @@ -1545,6 +1561,9 @@ pmap_pinit(pmap_t pmap)
  	TAILQ_INIT(&pmap->pm_pvchunk);
  	bzero(&pmap->pm_stats, sizeof pmap->pm_stats);
  
 +#ifdef HAMFISTED_LOCKING
 +	mtx_unlock(&createdelete_lock);
 +#endif
  	return (1);
  }
  
 @@ -1776,6 +1795,10 @@ pmap_release(pmap_t pmap)
  	    pmap->pm_stats.resident_count));
  	PT_UPDATES_FLUSH();
  
 +#ifdef HAMFISTED_LOCKING
 +	mtx_lock(&createdelete_lock);
 +#endif
 +
  	pmap_lazyfix(pmap);
  	mtx_lock_spin(&allpmaps_lock);
  	LIST_REMOVE(pmap, pm_list);
 @@ -1811,6 +1834,10 @@ pmap_release(pmap_t pmap)
  	pmap_qremove((vm_offset_t)pmap->pm_pdpt, 1);
  #endif
  	PMAP_LOCK_DESTROY(pmap);
 +
 +#ifdef HAMFISTED_LOCKING
 +	mtx_unlock(&createdelete_lock);
 +#endif
  }
  
  static int
 @@ -3136,6 +3163,10 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pm
  	CTR5(KTR_PMAP, "pmap_copy:  dst_pmap=%p src_pmap=%p dst_addr=0x%x len=%d src_addr=0x%x",
  	    dst_pmap, src_pmap, dst_addr, len, src_addr);
  	
 +#ifdef HAMFISTED_LOCKING
 +	mtx_lock(&createdelete_lock);
 +#endif
 +
  	vm_page_lock_queues();
  	if (dst_pmap < src_pmap) {
  		PMAP_LOCK(dst_pmap);
 @@ -3225,6 +3256,10 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pm
  	vm_page_unlock_queues();
  	PMAP_UNLOCK(src_pmap);
  	PMAP_UNLOCK(dst_pmap);
 +
 +#ifdef HAMFISTED_LOCKING
 +	mtx_unlock(&createdelete_lock);
 +#endif
  }	
  
  static __inline void
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