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Fix race in dnode_check_slots_free()

Currently, dnode_check_slots_free() works by checking dn->dn_type
in the dnode to determine if the dnode is reclaimable. However,
there is a small window of time between dnode_free_sync() in the
first call to dsl_dataset_sync() and when the useraccounting code
is run when the type is set DMU_OT_NONE, but the dnode is not yet
evictable, leading to crashes. This patch adds the ability for
dnodes to track which txg they were last dirtied in and adds a
check for this before performing the reclaim.

This patch also corrects several instances when dn_dirty_link was
treated as a list_node_t when it is technically a multilist_node_t.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7147
Closes #7388
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tcaputi authored and tonyhutter committed Apr 10, 2018
1 parent 1b0cd07 commit 60cea5dd49cab18c5d38b2d106d9a7fb972aa343
Showing with 43 additions and 11 deletions.
  1. +1 −0 include/sys/dmu_impl.h
  2. +4 −0 include/sys/dnode.h
  3. +3 −0 module/zfs/dbuf.c
  4. +1 −1 module/zfs/dmu.c
  5. +15 −0 module/zfs/dmu_objset.c
  6. +19 −10 module/zfs/dnode.c
@@ -161,6 +161,7 @@ extern "C" {
* dn_allocated_txg
* dn_free_txg
* dn_assigned_txg
* dn_dirty_txg
* dd_assigned_tx
* dn_notxholds
* dn_dirtyctx
@@ -260,6 +260,7 @@ struct dnode {
uint64_t dn_allocated_txg;
uint64_t dn_free_txg;
uint64_t dn_assigned_txg;
uint64_t dn_dirty_txg; /* txg dnode was last dirtied */
kcondvar_t dn_notxholds;
enum dnode_dirtycontext dn_dirtyctx;
uint8_t *dn_dirtyctx_firstset; /* dbg: contents meaningless */
@@ -362,6 +363,9 @@ void dnode_evict_dbufs(dnode_t *dn);
void dnode_evict_bonus(dnode_t *dn);
void dnode_free_interior_slots(dnode_t *dn);
#define DNODE_IS_DIRTY(_dn) \
((_dn)->dn_dirty_txg >= spa_syncing_txg((_dn)->dn_objset->os_spa))
#define DNODE_IS_CACHEABLE(_dn) \
((_dn)->dn_objset->os_primary_cache == ZFS_CACHE_ALL || \
(DMU_OT_IS_METADATA((_dn)->dn_type) && \
@@ -1606,6 +1606,9 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t *tx)
FTAG);
}
}
if (tx->tx_txg > dn->dn_dirty_txg)
dn->dn_dirty_txg = tx->tx_txg;
mutex_exit(&dn->dn_mtx);
if (db->db_blkid == DMU_SPILL_BLKID)
@@ -2044,7 +2044,7 @@ dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
* Check if dnode is dirty
*/
for (i = 0; i < TXG_SIZE; i++) {
if (list_link_active(&dn->dn_dirty_link[i])) {
if (multilist_link_active(&dn->dn_dirty_link[i])) {
clean = B_FALSE;
break;
}
@@ -1213,10 +1213,23 @@ dmu_objset_sync_dnodes(multilist_sublist_t *list, dmu_tx_t *tx)
ASSERT3U(dn->dn_nlevels, <=, DN_MAX_LEVELS);
multilist_sublist_remove(list, dn);
/*
* If we are not doing useraccounting (os_synced_dnodes == NULL)
* we are done with this dnode for this txg. Unset dn_dirty_txg
* if later txgs aren't dirtying it so that future holders do
* not get a stale value. Otherwise, we will do this in
* userquota_updates_task() when processing has completely
* finished for this txg.
*/
multilist_t *newlist = dn->dn_objset->os_synced_dnodes;
if (newlist != NULL) {
(void) dnode_add_ref(dn, newlist);
multilist_insert(newlist, dn);
} else {
mutex_enter(&dn->dn_mtx);
if (dn->dn_dirty_txg == tx->tx_txg)
dn->dn_dirty_txg = 0;
mutex_exit(&dn->dn_mtx);
}
dnode_sync(dn, tx);
@@ -1621,6 +1634,8 @@ userquota_updates_task(void *arg)
dn->dn_id_flags |= DN_ID_CHKED_BONUS;
}
dn->dn_id_flags &= ~(DN_ID_NEW_EXIST);
if (dn->dn_dirty_txg == spa_syncing_txg(os->os_spa))
dn->dn_dirty_txg = 0;
mutex_exit(&dn->dn_mtx);
multilist_sublist_remove(list, dn);
@@ -137,7 +137,7 @@ dnode_cons(void *arg, void *unused, int kmflag)
bzero(&dn->dn_next_blksz[0], sizeof (dn->dn_next_blksz));
for (i = 0; i < TXG_SIZE; i++) {
list_link_init(&dn->dn_dirty_link[i]);
multilist_link_init(&dn->dn_dirty_link[i]);
dn->dn_free_ranges[i] = NULL;
list_create(&dn->dn_dirty_records[i],
sizeof (dbuf_dirty_record_t),
@@ -147,6 +147,7 @@ dnode_cons(void *arg, void *unused, int kmflag)
dn->dn_allocated_txg = 0;
dn->dn_free_txg = 0;
dn->dn_assigned_txg = 0;
dn->dn_dirty_txg = 0;
dn->dn_dirtyctx = 0;
dn->dn_dirtyctx_firstset = NULL;
dn->dn_bonus = NULL;
@@ -184,7 +185,7 @@ dnode_dest(void *arg, void *unused)
ASSERT(!list_link_active(&dn->dn_link));
for (i = 0; i < TXG_SIZE; i++) {
ASSERT(!list_link_active(&dn->dn_dirty_link[i]));
ASSERT(!multilist_link_active(&dn->dn_dirty_link[i]));
ASSERT3P(dn->dn_free_ranges[i], ==, NULL);
list_destroy(&dn->dn_dirty_records[i]);
ASSERT0(dn->dn_next_nblkptr[i]);
@@ -199,6 +200,7 @@ dnode_dest(void *arg, void *unused)
ASSERT0(dn->dn_allocated_txg);
ASSERT0(dn->dn_free_txg);
ASSERT0(dn->dn_assigned_txg);
ASSERT0(dn->dn_dirty_txg);
ASSERT0(dn->dn_dirtyctx);
ASSERT3P(dn->dn_dirtyctx_firstset, ==, NULL);
ASSERT3P(dn->dn_bonus, ==, NULL);
@@ -523,6 +525,7 @@ dnode_destroy(dnode_t *dn)
dn->dn_allocated_txg = 0;
dn->dn_free_txg = 0;
dn->dn_assigned_txg = 0;
dn->dn_dirty_txg = 0;
dn->dn_dirtyctx = 0;
if (dn->dn_dirtyctx_firstset != NULL) {
@@ -592,6 +595,7 @@ dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
ASSERT0(dn->dn_maxblkid);
ASSERT0(dn->dn_allocated_txg);
ASSERT0(dn->dn_assigned_txg);
ASSERT0(dn->dn_dirty_txg);
ASSERT(refcount_is_zero(&dn->dn_tx_holds));
ASSERT3U(refcount_count(&dn->dn_holds), <=, 1);
ASSERT(avl_is_empty(&dn->dn_dbufs));
@@ -604,7 +608,7 @@ dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
ASSERT0(dn->dn_next_bonustype[i]);
ASSERT0(dn->dn_rm_spillblk[i]);
ASSERT0(dn->dn_next_blksz[i]);
ASSERT(!list_link_active(&dn->dn_dirty_link[i]));
ASSERT(!multilist_link_active(&dn->dn_dirty_link[i]));
ASSERT3P(list_head(&dn->dn_dirty_records[i]), ==, NULL);
ASSERT3P(dn->dn_free_ranges[i], ==, NULL);
}
@@ -779,6 +783,7 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
ndn->dn_allocated_txg = odn->dn_allocated_txg;
ndn->dn_free_txg = odn->dn_free_txg;
ndn->dn_assigned_txg = odn->dn_assigned_txg;
ndn->dn_dirty_txg = odn->dn_dirty_txg;
ndn->dn_dirtyctx = odn->dn_dirtyctx;
ndn->dn_dirtyctx_firstset = odn->dn_dirtyctx_firstset;
ASSERT(refcount_count(&odn->dn_tx_holds) == 0);
@@ -845,6 +850,7 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
odn->dn_allocated_txg = 0;
odn->dn_free_txg = 0;
odn->dn_assigned_txg = 0;
odn->dn_dirty_txg = 0;
odn->dn_dirtyctx = 0;
odn->dn_dirtyctx_firstset = NULL;
odn->dn_have_spill = B_FALSE;
@@ -1069,6 +1075,10 @@ dnode_check_slots_free(dnode_children_t *children, int idx, int slots)
{
ASSERT3S(idx + slots, <=, DNODES_PER_BLOCK);
/*
* If all dnode slots are either already free or
* evictable return B_TRUE.
*/
for (int i = idx; i < idx + slots; i++) {
dnode_handle_t *dnh = &children->dnc_children[i];
dnode_t *dn = dnh->dnh_dnode;
@@ -1077,18 +1087,17 @@ dnode_check_slots_free(dnode_children_t *children, int idx, int slots)
continue;
} else if (DN_SLOT_IS_PTR(dn)) {
mutex_enter(&dn->dn_mtx);
dmu_object_type_t type = dn->dn_type;
boolean_t can_free = (dn->dn_type == DMU_OT_NONE &&
!DNODE_IS_DIRTY(dn));
mutex_exit(&dn->dn_mtx);
if (type != DMU_OT_NONE)
if (!can_free)
return (B_FALSE);
continue;
else
continue;
} else {
return (B_FALSE);
}
return (B_FALSE);
}
return (B_TRUE);
@@ -1594,7 +1603,7 @@ dnode_setdirty(dnode_t *dn, dmu_tx_t *tx)
/*
* If we are already marked dirty, we're done.
*/
if (list_link_active(&dn->dn_dirty_link[txg & TXG_MASK])) {
if (multilist_link_active(&dn->dn_dirty_link[txg & TXG_MASK])) {
multilist_sublist_unlock(mls);
return;
}

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