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Track all lock relationships instead of pruning direct relationships

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if an indirect relationship exists (keep both A->B->C and A->C).
This allows witness_checkorder() to use isitmychild() instead of
the much more expensive isitmydescendant() to check for valid lock
ordering.

Don't do an expensive tree walk to update the w_level values when
the tree is updated.  Only update the w_level values when using the
debugger to display the tree.

Nuke the experimental "witness_watch > 1" mode that only compared
w_level for the two locks.  This information is no longer maintained
at run time, and the use of isitmychild() in witness_checkorder
should bring performance close enough to the acceptable level that
this hack is not needed.

Report witness data structure allocation statistics under the
debug.witness sysctl.

Reviewed by:	jhb
MFC after:	30 days
This commit is contained in:
Don Lewis 2005-08-25 03:47:37 +00:00
parent 00d101cf1f
commit 4053cae340
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=149441
1 changed files with 31 additions and 71 deletions
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102
sys/kern/subr_witness.c
View file

@ -165,10 +165,7 @@ static int insertchild(struct witness *parent, struct witness *child);
static int isitmychild(struct witness *parent, struct witness *child);
static int isitmydescendant(struct witness *parent, struct witness *child);
static int itismychild(struct witness *parent, struct witness *child);
static int rebalancetree(struct witness_list *list);
static void removechild(struct witness *parent, struct witness *child);
static int reparentchildren(struct witness *newparent,
struct witness *oldparent);
static int sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS);
static void witness_displaydescendants(void(*)(const char *fmt, ...),
struct witness *, int indent);
@ -194,11 +191,8 @@ static void witness_display(void(*)(const char *fmt, ...));
SYSCTL_NODE(_debug, OID_AUTO, witness, CTLFLAG_RW, 0, "Witness Locking");
/*
* If set to 0, witness is disabled. If set to 1, witness performs full lock
* order checking for all locks. If set to 2 or higher, then witness skips
* the full lock order check if the lock being acquired is at a higher level
* (i.e. farther down in the tree) than the current lock. This last mode is
* somewhat experimental and not considered fully safe. At runtime, this
* If set to 0, witness is disabled. If set to a non-zero value, witness
* performs full lock order checking for all locks. At runtime, this
* value may be set to 0 to turn off witness. witness is not allowed be
* turned on once it is turned off, however.
*/
@ -250,6 +244,16 @@ static struct witness_list w_sleep = STAILQ_HEAD_INITIALIZER(w_sleep);
static struct witness_child_list_entry *w_child_free = NULL;
static struct lock_list_entry *w_lock_list_free = NULL;
static int w_free_cnt, w_spin_cnt, w_sleep_cnt, w_child_free_cnt, w_child_cnt;
SYSCTL_INT(_debug_witness, OID_AUTO, free_cnt, CTLFLAG_RD, &w_free_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, spin_cnt, CTLFLAG_RD, &w_spin_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, sleep_cnt, CTLFLAG_RD, &w_sleep_cnt, 0,
"");
SYSCTL_INT(_debug_witness, OID_AUTO, child_free_cnt, CTLFLAG_RD,
&w_child_free_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, child_cnt, CTLFLAG_RD, &w_child_cnt, 0,
"");
static struct witness w_data[WITNESS_COUNT];
static struct witness_child_list_entry w_childdata[WITNESS_CHILDCOUNT];
static struct lock_list_entry w_locklistdata[LOCK_CHILDCOUNT];
@ -819,19 +823,12 @@ witness_checkorder(struct lock_object *lock, int flags, const char *file,
}
MPASS(!mtx_owned(&w_mtx));
mtx_lock_spin(&w_mtx);
/*
* If we have a known higher number just say ok
*/
if (witness_watch > 1 && w->w_level > w1->w_level) {
mtx_unlock_spin(&w_mtx);
return;
}
/*
* If we know that the the lock we are acquiring comes after
* the lock we most recently acquired in the lock order tree,
* then there is no need for any further checks.
*/
if (isitmydescendant(w1, w)) {
if (isitmychild(w1, w)) {
mtx_unlock_spin(&w_mtx);
return;
}
@ -1312,11 +1309,13 @@ enroll(const char *description, struct lock_class *lock_class)
w->w_class = lock_class;
w->w_refcount = 1;
STAILQ_INSERT_HEAD(&w_all, w, w_list);
if (lock_class->lc_flags & LC_SPINLOCK)
if (lock_class->lc_flags & LC_SPINLOCK) {
STAILQ_INSERT_HEAD(&w_spin, w, w_typelist);
else if (lock_class->lc_flags & LC_SLEEPLOCK)
w_spin_cnt++;
} else if (lock_class->lc_flags & LC_SLEEPLOCK) {
STAILQ_INSERT_HEAD(&w_sleep, w, w_typelist);
else {
w_sleep_cnt++;
} else {
mtx_unlock_spin(&w_mtx);
panic("lock class %s is not sleep or spin",
lock_class->lc_name);
@ -1334,10 +1333,13 @@ depart(struct witness *w)
struct witness *parent;
MPASS(w->w_refcount == 0);
if (w->w_class->lc_flags & LC_SLEEPLOCK)
if (w->w_class->lc_flags & LC_SLEEPLOCK) {
list = &w_sleep;
else
w_sleep_cnt--;
} else {
list = &w_spin;
w_spin_cnt--;
}
/*
* First, we run through the entire tree looking for any
* witnesses that the outgoing witness is a child of. For
@ -1348,8 +1350,6 @@ depart(struct witness *w)
if (!isitmychild(parent, w))
continue;
removechild(parent, w);
if (!reparentchildren(parent, w))
return (0);
}
/*
@ -1358,6 +1358,7 @@ depart(struct witness *w)
*/
for (wcl = w->w_children; wcl != NULL; wcl = nwcl) {
nwcl = wcl->wcl_next;
w_child_cnt--;
witness_child_free(wcl);
}
@ -1368,34 +1369,6 @@ depart(struct witness *w)
STAILQ_REMOVE(&w_all, w, witness, w_list);
witness_free(w);
/* Finally, fixup the tree. */
return (rebalancetree(list));
}
/*
* Prune an entire lock order tree. We look for cases where a lock
* is now both a descendant and a direct child of a given lock. In
* that case, we want to remove the direct child link from the tree.
*
* Returns false if insertchild() fails.
*/
static int
rebalancetree(struct witness_list *list)
{
struct witness *child, *parent;
STAILQ_FOREACH(child, list, w_typelist) {
STAILQ_FOREACH(parent, list, w_typelist) {
if (!isitmychild(parent, child))
continue;
removechild(parent, child);
if (isitmydescendant(parent, child))
continue;
if (!insertchild(parent, child))
return (0);
}
}
witness_levelall();
return (1);
}
@ -1420,31 +1393,13 @@ insertchild(struct witness *parent, struct witness *child)
*wcl = witness_child_get();
if (*wcl == NULL)
return (0);
w_child_cnt++;
}
(*wcl)->wcl_children[(*wcl)->wcl_count++] = child;
return (1);
}
/*
* Make all the direct descendants of oldparent be direct descendants
* of newparent.
*/
static int
reparentchildren(struct witness *newparent, struct witness *oldparent)
{
struct witness_child_list_entry *wcl;
int i;
/* Avoid making a witness a child of itself. */
MPASS(!isitmychild(oldparent, newparent));
for (wcl = oldparent->w_children; wcl != NULL; wcl = wcl->wcl_next)
for (i = 0; i < wcl->wcl_count; i++)
if (!insertchild(newparent, wcl->wcl_children[i]))
return (0);
return (1);
}
static int
itismychild(struct witness *parent, struct witness *child)
@ -1466,7 +1421,7 @@ itismychild(struct witness *parent, struct witness *child)
list = &w_sleep;
else
list = &w_spin;
return (rebalancetree(list));
return (1);
}
static void
@ -1490,6 +1445,7 @@ removechild(struct witness *parent, struct witness *child)
return;
wcl1 = *wcl;
*wcl = wcl1->wcl_next;
w_child_cnt--;
witness_child_free(wcl1);
}
@ -1648,6 +1604,7 @@ witness_get(void)
}
w = STAILQ_FIRST(&w_free);
STAILQ_REMOVE_HEAD(&w_free, w_list);
w_free_cnt--;
bzero(w, sizeof(*w));
return (w);
}
@ -1657,6 +1614,7 @@ witness_free(struct witness *w)
{
STAILQ_INSERT_HEAD(&w_free, w, w_list);
w_free_cnt++;
}
static struct witness_child_list_entry *
@ -1676,6 +1634,7 @@ witness_child_get(void)
return (NULL);
}
w_child_free = wcl->wcl_next;
w_child_free_cnt--;
bzero(wcl, sizeof(*wcl));
return (wcl);
}
@ -1686,6 +1645,7 @@ witness_child_free(struct witness_child_list_entry *wcl)
wcl->wcl_next = w_child_free;
w_child_free = wcl;
w_child_free_cnt++;
}
static struct lock_list_entry *