ceph: try to allocate enough memory for reserved caps

ceph_reserve_caps() may not reserve enough caps under high memory
pressure, but it saved the needed caps number that expected to
be reserved. When getting caps, crash would happen due to number
mismatch.

Now we will try to trim more caps when failing to allocate memory
for caps need to be reserved, then try again. If still failing to
allocate memory, return -ENOMEM.

Signed-off-by: Zhi Zhang <zhang.david2011@gmail.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 53 insertions, 8 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 1726ddcf5e34..8e66fb0e743d 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -154,13 +154,19 @@ void ceph_adjust_min_caps(struct ceph_mds_client *mdsc, int delta)
 	spin_unlock(&mdsc->caps_list_lock);
 }
 
-void ceph_reserve_caps(struct ceph_mds_client *mdsc,
+/*
+ * Called under mdsc->mutex.
+ */
+int ceph_reserve_caps(struct ceph_mds_client *mdsc,
 		      struct ceph_cap_reservation *ctx, int need)
 {
-	int i;
+	int i, j;
 	struct ceph_cap *cap;
 	int have;
 	int alloc = 0;
+	int max_caps;
+	bool trimmed = false;
+	struct ceph_mds_session *s;
 	LIST_HEAD(newcaps);
 
 	dout("reserve caps ctx=%p need=%d\n", ctx, need);
@@ -179,16 +185,37 @@ void ceph_reserve_caps(struct ceph_mds_client *mdsc,
 	spin_unlock(&mdsc->caps_list_lock);
 
 	for (i = have; i < need; i++) {
+retry:
 		cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
-		if (!cap)
-			break;
+		if (!cap) {
+			if (!trimmed) {
+				for (j = 0; j < mdsc->max_sessions; j++) {
+					s = __ceph_lookup_mds_session(mdsc, j);
+					if (!s)
+						continue;
+					mutex_unlock(&mdsc->mutex);
+
+					mutex_lock(&s->s_mutex);
+					max_caps = s->s_nr_caps - (need - i);
+					ceph_trim_caps(mdsc, s, max_caps);
+					mutex_unlock(&s->s_mutex);
+
+					ceph_put_mds_session(s);
+					mutex_lock(&mdsc->mutex);
+				}
+				trimmed = true;
+				goto retry;
+			} else {
+				pr_warn("reserve caps ctx=%p ENOMEM "
+					"need=%d got=%d\n",
+					ctx, need, have + alloc);
+				goto out_nomem;
+			}
+		}
 		list_add(&cap->caps_item, &newcaps);
 		alloc++;
 	}
-	/* we didn't manage to reserve as much as we needed */
-	if (have + alloc != need)
-		pr_warn("reserve caps ctx=%p ENOMEM need=%d got=%d\n",
-			ctx, need, have + alloc);
+	BUG_ON(have + alloc != need);
 
 	spin_lock(&mdsc->caps_list_lock);
 	mdsc->caps_total_count += alloc;
@@ -204,6 +231,24 @@ void ceph_reserve_caps(struct ceph_mds_client *mdsc,
 	dout("reserve caps ctx=%p %d = %d used + %d resv + %d avail\n",
 	     ctx, mdsc->caps_total_count, mdsc->caps_use_count,
 	     mdsc->caps_reserve_count, mdsc->caps_avail_count);
+	return 0;
+
+out_nomem:
+	while (!list_empty(&newcaps)) {
+		cap = list_first_entry(&newcaps,
+				struct ceph_cap, caps_item);
+		list_del(&cap->caps_item);
+		kmem_cache_free(ceph_cap_cachep, cap);
+	}
+
+	spin_lock(&mdsc->caps_list_lock);
+	mdsc->caps_avail_count += have;
+	mdsc->caps_reserve_count -= have;
+	BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
+					 mdsc->caps_reserve_count +
+					 mdsc->caps_avail_count);
+	spin_unlock(&mdsc->caps_list_lock);
+	return -ENOMEM;
 }
 
 int ceph_unreserve_caps(struct ceph_mds_client *mdsc,