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Implement a variant locking scheme for vm maps: Access to system maps

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is now synchronized by a mutex, whereas access to user maps is still
synchronized by a lockmgr()-based lock.  Why?  No single type of lock,
including sx locks, meets the requirements of both types of vm map.
Sometimes we sleep while holding the lock on a user map.  Thus, a
a mutex isn't appropriate.  On the other hand, both lockmgr()-based
and sx locks release Giant when a thread/process blocks during
contention for a lock.  This could lead to a race condition in a legacy
driver (that relies on Giant for synchronization) if it attempts to
kmem_malloc() and fails to immediately obtain the lock.  Fortunately,
we never sleep while holding a system map lock.
This commit is contained in:
Alan Cox 2002-12-31 19:38:04 +00:00
parent d43f696c1c
commit 36daaecd04
2 changed files with 39 additions and 16 deletions
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54
sys/vm/vm_map.c
View File

@ -197,7 +197,7 @@ vm_map_zfini(void *mem, int size)
vm_map_t map;
map = (vm_map_t)mem;
mtx_destroy(&map->system_mtx);
lockdestroy(&map->lock);
}
@ -210,6 +210,7 @@ vm_map_zinit(void *mem, int size)
map->nentries = 0;
map->size = 0;
map->infork = 0;
mtx_init(&map->system_mtx, "system map", NULL, MTX_DEF);
lockinit(&map->lock, PVM, "thrd_sleep", 0, LK_NOPAUSE);
}
@ -375,9 +376,11 @@ _vm_map_lock(vm_map_t map, const char *file, int line)
int error;
if (map->system_map)
GIANT_REQUIRED;
error = lockmgr(&map->lock, LK_EXCLUSIVE, NULL, curthread);
KASSERT(error == 0, ("%s: failed to get lock", __func__));
_mtx_lock_flags(&map->system_mtx, 0, file, line);
else {
error = lockmgr(&map->lock, LK_EXCLUSIVE, NULL, curthread);
KASSERT(error == 0, ("%s: failed to get lock", __func__));
}
map->timestamp++;
}
@ -385,7 +388,10 @@ void
_vm_map_unlock(vm_map_t map, const char *file, int line)
{
lockmgr(&map->lock, LK_RELEASE, NULL, curthread);
if (map->system_map)
_mtx_unlock_flags(&map->system_mtx, 0, file, line);
else
lockmgr(&map->lock, LK_RELEASE, NULL, curthread);
}
void
@ -394,16 +400,21 @@ _vm_map_lock_read(vm_map_t map, const char *file, int line)
int error;
if (map->system_map)
GIANT_REQUIRED;
error = lockmgr(&map->lock, LK_EXCLUSIVE, NULL, curthread);
KASSERT(error == 0, ("%s: failed to get lock", __func__));
_mtx_lock_flags(&map->system_mtx, 0, file, line);
else {
error = lockmgr(&map->lock, LK_EXCLUSIVE, NULL, curthread);
KASSERT(error == 0, ("%s: failed to get lock", __func__));
}
}
void
_vm_map_unlock_read(vm_map_t map, const char *file, int line)
{
lockmgr(&map->lock, LK_RELEASE, NULL, curthread);
if (map->system_map)
_mtx_unlock_flags(&map->system_mtx, 0, file, line);
else
lockmgr(&map->lock, LK_RELEASE, NULL, curthread);
}
int
@ -411,9 +422,9 @@ _vm_map_trylock(vm_map_t map, const char *file, int line)
{
int error;
if (map->system_map)
GIANT_REQUIRED;
error = lockmgr(&map->lock, LK_EXCLUSIVE | LK_NOWAIT, NULL, curthread);
error = map->system_map ?
!_mtx_trylock(&map->system_mtx, 0, file, line) :
lockmgr(&map->lock, LK_EXCLUSIVE | LK_NOWAIT, NULL, curthread);
if (error == 0)
map->timestamp++;
return (error == 0);
@ -423,8 +434,13 @@ int
_vm_map_lock_upgrade(vm_map_t map, const char *file, int line)
{
KASSERT(lockstatus(&map->lock, curthread) == LK_EXCLUSIVE,
("%s: lock not held", __func__));
if (map->system_map) {
#ifdef INVARIANTS
_mtx_assert(&map->system_mtx, MA_OWNED, file, line);
#endif
} else
KASSERT(lockstatus(&map->lock, curthread) == LK_EXCLUSIVE,
("%s: lock not held", __func__));
map->timestamp++;
return (0);
}
@ -433,8 +449,13 @@ void
_vm_map_lock_downgrade(vm_map_t map, const char *file, int line)
{
KASSERT(lockstatus(&map->lock, curthread) == LK_EXCLUSIVE,
("%s: lock not held", __func__));
if (map->system_map) {
#ifdef INVARIANTS
_mtx_assert(&map->system_mtx, MA_OWNED, file, line);
#endif
} else
KASSERT(lockstatus(&map->lock, curthread) == LK_EXCLUSIVE,
("%s: lock not held", __func__));
}
/*
@ -514,6 +535,7 @@ void
vm_map_init(vm_map_t map, vm_offset_t min, vm_offset_t max)
{
_vm_map_init(map, min, max);
mtx_init(&map->system_mtx, "system map", NULL, MTX_DEF);
lockinit(&map->lock, PVM, "thrd_sleep", 0, LK_NOPAUSE);
}

1
sys/vm/vm_map.h
View File

@ -164,6 +164,7 @@ vm_map_entry_behavior(vm_map_entry_t entry)
struct vm_map {
struct vm_map_entry header; /* List of entries */
struct lock lock; /* Lock for map data */
struct mtx system_mtx;
int nentries; /* Number of entries */
vm_size_t size; /* virtual size */
u_char needs_wakeup;