Bug #764

panic in zfs:dbuf_sync_list

Added by Gordon Ross over 7 years ago. Updated over 7 years ago.

Status:ResolvedStart date:2011-03-03
Priority:HighDue date:
Assignee:Gordon Ross% Done:


Target version:-
Difficulty: Tags:


Workload is Robocopy on Windows connected to a CIFS share,
and writing lots of files onto ZFS. Get panics like:

BAD TRAP: type=e (#pf Page fault) rp=ffffff0046ac67c0 addr=108 occurred in modul
e "zfs" due to a NULL pointer dereference

ffffff0046ac68e0 zfs:dbuf_sync_list+46 ()
ffffff0046ac6950 zfs:dnode_sync+377 ()
ffffff0046ac69a0 zfs:dmu_objset_sync_dnodes+80 ()
ffffff0046ac6a30 zfs:dmu_objset_sync+1da ()
ffffff0046ac6a70 zfs:dsl_dataset_sync+5d ()
ffffff0046ac6af0 zfs:dsl_pool_sync+c0 ()
ffffff0046ac6ba0 zfs:spa_sync+37b ()
ffffff0046ac6c40 zfs:txg_sync_thread+247 ()
ffffff0046ac6c50 unix:thread_start+8 ()


#1 Updated by Gordon Ross over 7 years ago

It's been suggested that this bug may be related:
(mkfile can trigger various dmu panics when file has spill block)

The common factor is replacing ACLs that are large enough
so the are stored in ZFS "spill" blocks.

#2 Updated by Gordon Ross over 7 years ago

Hypothesis about what's going on here.

At some time in the past, something, i.e. dnode_reallocate()
calls one of:
dbuf_rm_spill(dn, tx);

These will do:
dbuf_rm_spill(dnode_t *dn, dmu_tx_t *tx)
dbuf_free_range(dn, DMU_SPILL_BLKID, DMU_SPILL_BLKID, tx)
dbuf_undirty(db, tx)

Currently dbuf_undirty can leave a spill block in dn_dirty_records[],
(it having been put there previously by dbuf_dirty) and free it.
Sometime later, dbuf_sync_list trips over this reference to free'd
(and typically reused) memory.

Also, dbuf_undirty can call dnode_clear_range with a bogus
block ID. It needs to test for DMU_SPILL_BLKID, similar to
how dnode_clear_range is called in dbuf_dirty().

#3 Updated by Gordon Ross over 7 years ago

  • Status changed from New to Resolved

Fix pushed to illumos-gate:
changeset: 13298:c234f438c0d3
tag: tip
user: Gordon Ross <>
date: Tue Mar 08 16:39:19 2011 -0500
764 panic in zfs:dbuf_sync_list
Reviewed by: George Wilson <>
Reviewed by:
Reviewed by: Albert Lee <
Approved by: Garrett D'Amore <>

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