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authorSverker Eriksson <[email protected]>2015-06-26 14:22:14 +0200
committerSverker Eriksson <[email protected]>2015-06-26 14:22:14 +0200
commit37a9aa5f35466838af383d53490b040142468673 (patch)
tree085c03703e6c422e4f78ba5dc58669f688a2dbe0 /erts/emulator/beam/erl_db_hash.c
parent74a95b3d511177a9b35c2b0272b9ca5511b6f750 (diff)
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erts: Fix ETS race between object deleter and table unfixer
causing the delete marked object to be left in the table after safe_fixtable(_,false) has returned. This is not super serious as the delete marked object is quite benign and will be deleted at the next unfix operation.
Diffstat (limited to 'erts/emulator/beam/erl_db_hash.c')
-rw-r--r--erts/emulator/beam/erl_db_hash.c60
1 files changed, 37 insertions, 23 deletions
diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c
index 81b0c4465c..98a2e2842a 100644
--- a/erts/emulator/beam/erl_db_hash.c
+++ b/erts/emulator/beam/erl_db_hash.c
@@ -148,8 +148,11 @@ static ERTS_INLINE Uint hash_to_ix(DbTableHash* tb, HashValue hval)
}
/* Remember a slot containing a pseudo-deleted item (INVALID_HASH)
-*/
-static ERTS_INLINE void add_fixed_deletion(DbTableHash* tb, int ix)
+ * Return false if we got raced by unfixing thread
+ * and the object should be deleted for real.
+ */
+static ERTS_INLINE int add_fixed_deletion(DbTableHash* tb, int ix,
+ erts_aint_t fixated_by_me)
{
erts_aint_t was_next;
erts_aint_t exp_next;
@@ -160,12 +163,18 @@ static ERTS_INLINE void add_fixed_deletion(DbTableHash* tb, int ix)
fixd->slot = ix;
was_next = erts_smp_atomic_read_acqb(&tb->fixdel);
do { /* Lockless atomic insertion in linked list: */
- exp_next = was_next;
+ if (NFIXED(tb) <= fixated_by_me) {
+ erts_db_free(ERTS_ALC_T_DB_FIX_DEL, (DbTable*)tb,
+ fixd, sizeof(FixedDeletion));
+ return 0; /* raced by unfixer */
+ }
+ exp_next = was_next;
fixd->next = (FixedDeletion*) exp_next;
- was_next = erts_smp_atomic_cmpxchg_relb(&tb->fixdel,
- (erts_aint_t) fixd,
- exp_next);
+ was_next = erts_smp_atomic_cmpxchg_mb(&tb->fixdel,
+ (erts_aint_t) fixd,
+ exp_next);
}while (was_next != exp_next);
+ return 1;
}
@@ -607,8 +616,8 @@ void db_unfix_table_hash(DbTableHash *tb)
|| (erts_smp_lc_rwmtx_is_rlocked(&tb->common.rwlock)
&& !tb->common.is_thread_safe));
restart:
- fixdel = (FixedDeletion*) erts_smp_atomic_xchg_acqb(&tb->fixdel,
- (erts_aint_t) NULL);
+ fixdel = (FixedDeletion*) erts_smp_atomic_xchg_mb(&tb->fixdel,
+ (erts_aint_t) NULL);
while (fixdel != NULL) {
FixedDeletion *fx = fixdel;
int ix = fx->slot;
@@ -1142,9 +1151,9 @@ int db_erase_hash(DbTable *tbl, Eterm key, Eterm *ret)
while(b != 0) {
if (has_live_key(tb,b,key,hval)) {
--nitems_diff;
- if (nitems_diff == -1 && IS_FIXED(tb)) {
+ if (nitems_diff == -1 && IS_FIXED(tb)
+ && add_fixed_deletion(tb, ix, 0)) {
/* Pseudo remove (no need to keep several of same key) */
- add_fixed_deletion(tb, ix);
b->hvalue = INVALID_HASH;
} else {
*bp = b->next;
@@ -1196,9 +1205,8 @@ static int db_erase_object_hash(DbTable *tbl, Eterm object, Eterm *ret)
++nkeys;
if (db_eq(&tb->common,object, &b->dbterm)) {
--nitems_diff;
- if (nkeys==1 && IS_FIXED(tb)) { /* Pseudo remove */
- add_fixed_deletion(tb,ix);
- b->hvalue = INVALID_HASH;
+ if (nkeys==1 && IS_FIXED(tb) && add_fixed_deletion(tb,ix,0)) {
+ b->hvalue = INVALID_HASH; /* Pseudo remove */
bp = &b->next;
b = b->next;
} else {
@@ -1820,14 +1828,17 @@ static int db_select_delete_hash(Process *p,
int did_erase = 0;
if (db_match_dbterm(&tb->common, p, mpi.mp, 0,
&(*current)->dbterm, NULL, 0) == am_true) {
+ HashDbTerm *del;
if (NFIXED(tb) > fixated_by_me) { /* fixated by others? */
if (slot_ix != last_pseudo_delete) {
- add_fixed_deletion(tb, slot_ix);
- last_pseudo_delete = slot_ix;
+ if (!add_fixed_deletion(tb, slot_ix, fixated_by_me))
+ goto do_erase;
+ last_pseudo_delete = slot_ix;
}
(*current)->hvalue = INVALID_HASH;
} else {
- HashDbTerm *del = *current;
+ do_erase:
+ del = *current;
*current = (*current)->next;
free_term(tb, del);
did_erase = 1;
@@ -1931,14 +1942,17 @@ static int db_select_delete_continue_hash(Process *p,
int did_erase = 0;
if (db_match_dbterm(&tb->common, p, mp, 0,
&(*current)->dbterm, NULL, 0) == am_true) {
+ HashDbTerm *del;
if (NFIXED(tb) > fixated_by_me) { /* fixated by others? */
if (slot_ix != last_pseudo_delete) {
- add_fixed_deletion(tb, slot_ix);
+ if (!add_fixed_deletion(tb, slot_ix, fixated_by_me))
+ goto do_erase;
last_pseudo_delete = slot_ix;
}
(*current)->hvalue = INVALID_HASH;
} else {
- HashDbTerm *del = *current;
+ do_erase:
+ del = *current;
*current = (*current)->next;
free_term(tb, del);
did_erase = 1;
@@ -2089,9 +2103,9 @@ static int db_take_hash(Process *p, DbTable *tbl, Eterm key, Eterm *ret)
*ret = get_term_list(p, tb, key, hval, b, &bend);
while (b != bend) {
--nitems_diff;
- if (nitems_diff == -1 && IS_FIXED(tb)) {
+ if (nitems_diff == -1 && IS_FIXED(tb)
+ && add_fixed_deletion(tb, ix, 0)) {
/* Pseudo remove (no need to keep several of same key) */
- add_fixed_deletion(tb, ix);
bp = &b->next;
b->hvalue = INVALID_HASH;
b = b->next;
@@ -2131,7 +2145,7 @@ int db_mark_all_deleted_hash(DbTable *tbl)
for (i = 0; i < NACTIVE(tb); i++) {
if ((list = BUCKET(tb,i)) != NULL) {
- add_fixed_deletion(tb, i);
+ add_fixed_deletion(tb, i, 0);
do {
list->hvalue = INVALID_HASH;
list = list->next;
@@ -2908,8 +2922,8 @@ db_finalize_dbterm_hash(int cret, DbUpdateHandle* handle)
ASSERT((&b->dbterm == handle->dbterm) == !(tb->common.compress && handle->flags & DB_MUST_RESIZE));
if (handle->flags & DB_NEW_OBJECT && cret != DB_ERROR_NONE) {
- if (IS_FIXED(tb)) {
- add_fixed_deletion(tb, hash_to_ix(tb, b->hvalue));
+ if (IS_FIXED(tb) && add_fixed_deletion(tb, hash_to_ix(tb, b->hvalue),
+ 0)) {
b->hvalue = INVALID_HASH;
} else {
*bp = b->next;