svn commit: r368189 - head/sys/vm
Mark Johnston
markj at FreeBSD.org
Mon Nov 30 16:18:34 UTC 2020
Author: markj
Date: Mon Nov 30 16:18:33 2020
New Revision: 368189
URL: https://svnweb.freebsd.org/changeset/base/368189
Log:
uma: Avoid allocating buckets with the cross-domain lock held
Allocation of a bucket can trigger a cross-domain free in the bucket
zone, e.g., if the per-CPU alloc bucket is empty, we free it and get
migrated to a remote domain. This can lead to deadlocks since a bucket
zone may allocate buckets from itself or a pair of bucket zones could be
allocating from each other.
Fix the problem by dropping the cross-domain lock before allocating a
new bucket and handling refill races. Use a list of empty buckets to
ensure that we can make forward progress.
Reported by: imp, mjg (witness(9) warnings)
Discussed with: jeff
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D27341
Modified:
head/sys/vm/uma_core.c
Modified: head/sys/vm/uma_core.c
==============================================================================
--- head/sys/vm/uma_core.c Mon Nov 30 15:04:35 2020 (r368188)
+++ head/sys/vm/uma_core.c Mon Nov 30 16:18:33 2020 (r368189)
@@ -4250,7 +4250,7 @@ zfree_item:
static void
zone_free_cross(uma_zone_t zone, uma_bucket_t bucket, void *udata)
{
- struct uma_bucketlist fullbuckets;
+ struct uma_bucketlist emptybuckets, fullbuckets;
uma_zone_domain_t zdom;
uma_bucket_t b;
smr_seq_t seq;
@@ -4274,31 +4274,57 @@ zone_free_cross(uma_zone_t zone, uma_bucket_t bucket,
* lock on the current crossfree bucket. A full matrix with
* per-domain locking could be used if necessary.
*/
+ STAILQ_INIT(&emptybuckets);
STAILQ_INIT(&fullbuckets);
ZONE_CROSS_LOCK(zone);
- while (bucket->ub_cnt > 0) {
+ for (; bucket->ub_cnt > 0; bucket->ub_cnt--) {
item = bucket->ub_bucket[bucket->ub_cnt - 1];
domain = item_domain(item);
zdom = ZDOM_GET(zone, domain);
if (zdom->uzd_cross == NULL) {
- zdom->uzd_cross = bucket_alloc(zone, udata, M_NOWAIT);
- if (zdom->uzd_cross == NULL)
- break;
+ if ((b = STAILQ_FIRST(&emptybuckets)) != NULL) {
+ STAILQ_REMOVE_HEAD(&emptybuckets, ub_link);
+ zdom->uzd_cross = b;
+ } else {
+ /*
+ * Avoid allocating a bucket with the cross lock
+ * held, since allocation can trigger a
+ * cross-domain free and bucket zones may
+ * allocate from each other.
+ */
+ ZONE_CROSS_UNLOCK(zone);
+ b = bucket_alloc(zone, udata, M_NOWAIT);
+ if (b == NULL)
+ goto out;
+ ZONE_CROSS_LOCK(zone);
+ if (zdom->uzd_cross != NULL) {
+ STAILQ_INSERT_HEAD(&emptybuckets, b,
+ ub_link);
+ } else {
+ zdom->uzd_cross = b;
+ }
+ }
}
b = zdom->uzd_cross;
b->ub_bucket[b->ub_cnt++] = item;
b->ub_seq = seq;
if (b->ub_cnt == b->ub_entries) {
STAILQ_INSERT_HEAD(&fullbuckets, b, ub_link);
- zdom->uzd_cross = NULL;
+ if ((b = STAILQ_FIRST(&emptybuckets)) != NULL)
+ STAILQ_REMOVE_HEAD(&emptybuckets, ub_link);
+ zdom->uzd_cross = b;
}
- bucket->ub_cnt--;
}
ZONE_CROSS_UNLOCK(zone);
+out:
if (bucket->ub_cnt == 0)
bucket->ub_seq = SMR_SEQ_INVALID;
bucket_free(zone, bucket, udata);
+ while ((b = STAILQ_FIRST(&emptybuckets)) != NULL) {
+ STAILQ_REMOVE_HEAD(&emptybuckets, ub_link);
+ bucket_free(zone, b, udata);
+ }
while ((b = STAILQ_FIRST(&fullbuckets)) != NULL) {
STAILQ_REMOVE_HEAD(&fullbuckets, ub_link);
domain = item_domain(b->ub_bucket[0]);
More information about the svn-src-all
mailing list