Fix stack ddt_class_contains()

Stack usage for ddt_class_contains() reduced from 524 bytes to 68
bytes.  This large stack allocation significantly contributed to
the likelyhood of a stack overflow when scrubbing/resilvering
dedup pools.

diff --git a/module/zfs/ddt.c b/module/zfs/ddt.c
index 49428d109f7e379a9acc6d62839d2093b610ca92..7279f1d5dc0785443230120d82443f1d7c18612e 100644 (file)
--- a/module/zfs/ddt.c
+++ b/module/zfs/ddt.c
@@ -891,7 +891,7 @@ boolean_t
 ddt_class_contains(spa_t *spa, enum ddt_class max_class, const blkptr_t *bp)
 {
        ddt_t *ddt;
-       ddt_entry_t dde;
+       ddt_entry_t *dde;
        enum ddt_type type;
        enum ddt_class class;
 
@@ -902,14 +902,20 @@ ddt_class_contains(spa_t *spa, enum ddt_class max_class, const blkptr_t *bp)
                return (B_TRUE);
 
        ddt = spa->spa_ddt[BP_GET_CHECKSUM(bp)];
+       dde = kmem_alloc(sizeof(ddt_entry_t), KM_SLEEP);
 
-       ddt_key_fill(&dde.dde_key, bp);
+       ddt_key_fill(&(dde->dde_key), bp);
 
-       for (type = 0; type < DDT_TYPES; type++)
-               for (class = 0; class <= max_class; class++)
-                       if (ddt_object_lookup(ddt, type, class, &dde) == 0)
+       for (type = 0; type < DDT_TYPES; type++) {
+               for (class = 0; class <= max_class; class++) {
+                       if (ddt_object_lookup(ddt, type, class, dde) == 0) {
+                               kmem_free(dde, sizeof(ddt_entry_t));
                                return (B_TRUE);
+                       }
+               }
+       }
 
+       kmem_free(dde, sizeof(ddt_entry_t));
        return (B_FALSE);
 }