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Fix a deadlock cause by a lock ordering interaction between pmap_enter() 

and pmap_growkernel().
This commit is contained in:
thorpej 2001-05-05 18:22:04 +00:00
parent d493d86cac
commit 18c5f91b0b
1 changed files with 45 additions and 12 deletions
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57
sys/arch/alpha/alpha/pmap.c
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@ -1,4 +1,4 @@
/* $NetBSD: pmap.c,v 1.178 2001/05/01 05:53:29 ross Exp $ */
/* $NetBSD: pmap.c,v 1.179 2001/05/05 18:22:04 thorpej Exp $ */
/*-
* Copyright (c) 1998, 1999, 2000, 2001 The NetBSD Foundation, Inc.
@ -154,7 +154,7 @@
#include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.178 2001/05/01 05:53:29 ross Exp $");
__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.179 2001/05/05 18:22:04 thorpej Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@ -372,6 +372,18 @@ struct pmap_asn_info pmap_asn_info[ALPHA_MAXPROCS];
* * pmap_growkernel_slock - This lock protects pmap_growkernel()
* and the virtual_end variable.
*
* There is a lock ordering constraint for pmap_growkernel_slock.
* pmap_growkernel() acquires the locks in the following order:
*
* pmap_growkernel_slock -> pmap_all_pmaps_slock ->
* pmap->pm_slock
*
* But pmap_lev1map_create() is called with pmap->pm_slock held,
* and also needs to acquire the pmap_growkernel_slock. So,
* we require that the caller of pmap_lev1map_create() (currently,
* the only caller is pmap_enter()) acquire pmap_growkernel_slock
* before acquring pmap->pm_slock.
*
* Address space number management (global ASN counters and per-pmap
* ASN state) are not locked; they use arrays of values indexed
* per-processor.
@ -1679,7 +1691,23 @@ pmap_enter(pmap_t pmap, vaddr_t va, paddr_t pa, vm_prot_t prot, int flags)
* created.
*/
if (pmap->pm_lev1map == kernel_lev1map) {
/*
* XXX Yuck.
* We have to unlock the pmap, lock the
* pmap_growkernel_slock, and re-lock the
* pmap here, in order to avoid a deadlock
* with pmap_growkernel().
*
* Because we unlock, we have a window for
* someone else to add a mapping, thus creating
* a level 1 map; pmap_lev1map_create() checks
* for this condition.
*/
PMAP_UNLOCK(pmap);
simple_lock(&pmap_growkernel_slock);
PMAP_LOCK(pmap);
error = pmap_lev1map_create(pmap, cpu_id);
simple_unlock(&pmap_growkernel_slock);
if (error) {
if (flags & PMAP_CANFAIL)
goto out;
@ -3231,7 +3259,7 @@ pmap_growkernel(vaddr_t maxkvaddr)
*
* Create a new level 1 page table for the specified pmap.
*
* Note: the pmap must already be locked.
* Note: growkernel and the pmap must already be locked.
*/
int
pmap_lev1map_create(pmap_t pmap, long cpu_id)
@ -3241,23 +3269,28 @@ pmap_lev1map_create(pmap_t pmap, long cpu_id)
#ifdef DIAGNOSTIC
if (pmap == pmap_kernel())
panic("pmap_lev1map_create: got kernel pmap");
#endif
if (pmap->pm_lev1map != kernel_lev1map) {
/*
* We have to briefly unlock the pmap in pmap_enter()
* do deal with a lock ordering constraint, so it's
* entirely possible for this to happen.
*/
return (0);
}
#ifdef DIAGNOSTIC
if (pmap->pm_asni[cpu_id].pma_asn != PMAP_ASN_RESERVED)
panic("pmap_lev1map_create: pmap uses non-reserved ASN");
#endif
simple_lock(&pmap_growkernel_slock);
l1pt = pool_cache_get(&pmap_l1pt_cache, PR_NOWAIT);
if (l1pt == NULL) {
simple_unlock(&pmap_growkernel_slock);
return ENOMEM;
}
if (l1pt == NULL)
return (ENOMEM);
pmap->pm_lev1map = l1pt;
simple_unlock(&pmap_growkernel_slock);
/*
* The page table base has changed; if the pmap was active,
* reactivate it.
@ -3267,7 +3300,7 @@ pmap_lev1map_create(pmap_t pmap, long cpu_id)
PMAP_ACTIVATE(pmap, curproc, cpu_id);
}
PMAP_LEV1MAP_SHOOTDOWN(pmap, cpu_id);
return 0;
return (0);
}
/*