[src/trunk]: src/sys/arch/i386/i386 Fix a silly MP race condition introduced ...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4db1edbe1e98
branches:  trunk
changeset: 500196:4db1edbe1e98
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Thu Dec 07 21:53:46 2000 +0000

description:
Fix a silly MP race condition introduced in the previous.

diffstat:

 sys/arch/i386/i386/pmap.c |  42 +++++++++++++++++++++++++++---------------
 1 files changed, 27 insertions(+), 15 deletions(-)

diffs (91 lines):

diff -r e52358564468 -r 4db1edbe1e98 sys/arch/i386/i386/pmap.c
--- a/sys/arch/i386/i386/pmap.c Thu Dec 07 21:48:58 2000 +0000
+++ b/sys/arch/i386/i386/pmap.c Thu Dec 07 21:53:46 2000 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap.c,v 1.114 2000/12/07 20:19:05 thorpej Exp $       */
+/*     $NetBSD: pmap.c,v 1.115 2000/12/07 21:53:46 thorpej Exp $       */
 
 /*
  *
@@ -69,6 +69,7 @@
 #include <sys/malloc.h>
 #include <sys/pool.h>
 #include <sys/user.h>
+#include <sys/kernel.h>
 
 #include <uvm/uvm.h>
 
@@ -1739,6 +1740,11 @@
        pd_entry_t *pdir = object;
        paddr_t pdirpa;
 
+       /*
+        * NOTE: The `pmap_lock' is held when the PDP is allocated.
+        * WE MUST NOT BLOCK!
+        */
+
        /* fetch the physical address of the page directory. */
        (void) pmap_extract(pmap_kernel(), (vaddr_t) pdir, &pdirpa);
 
@@ -1748,14 +1754,6 @@
        /* put in recursibve PDE to map the PTEs */
        pdir[PDSLOT_PTE] = pdirpa | PG_V | PG_KW;
 
-       /*
-        * we need to lock pmaps_lock to prevent nkpde from changing on
-        * us.  note that there is no need to splimp to protect us from
-        * malloc since malloc allocates out of a submap and we should
-        * have already allocated kernel PTPs to cover the range...
-        */
-       simple_lock(&pmaps_lock);
-
        /* put in kernel VM PDEs */
        memcpy(&pdir[PDSLOT_KERN], &PDP_BASE[PDSLOT_KERN],
            nkpde * sizeof(pd_entry_t));
@@ -1764,8 +1762,6 @@
        memset(&pdir[PDSLOT_KERN + nkpde], 0,
            PAGE_SIZE - ((PDSLOT_KERN + nkpde) * sizeof(pd_entry_t)));
 
-       simple_unlock(&pmaps_lock);
-
        return (0);
 }
 
@@ -1794,17 +1790,33 @@
        pmap->pm_ptphint = NULL;
        pmap->pm_flags = 0;
 
-       /* allocate PDP */
-       pmap->pm_pdir = pool_cache_get(&pmap_pdp_cache, PR_WAITOK);
-       pmap->pm_pdirpa = pmap->pm_pdir[PDSLOT_PTE] & PG_FRAME;
-
        /* init the LDT */
        pmap->pm_ldt = NULL;
        pmap->pm_ldt_len = 0;
        pmap->pm_ldt_sel = GSEL(GLDT_SEL, SEL_KPL);
 
+       /* allocate PDP */
+
+       /*
+        * we need to lock pmaps_lock to prevent nkpde from changing on
+        * us.  note that there is no need to splimp to protect us from
+        * malloc since malloc allocates out of a submap and we should
+        * have already allocated kernel PTPs to cover the range...
+        *
+        * NOTE: WE MUST NOT BLOCK WHILE HOLDING THE `pmap_lock'!
+        */
+
        simple_lock(&pmaps_lock);
+
+       /* XXX Need a generic "I want memory" wchan */
+       while ((pmap->pm_pdir =
+           pool_cache_get(&pmap_pdp_cache, PR_NOWAIT)) == NULL)
+               (void) ltsleep(&lbolt, PVM, "pmapcr", hz >> 3, &pmaps_lock);
+
+       pmap->pm_pdirpa = pmap->pm_pdir[PDSLOT_PTE] & PG_FRAME;
+
        LIST_INSERT_HEAD(&pmaps, pmap, pm_list);
+
        simple_unlock(&pmaps_lock);
 
        return (pmap);