From 81edd3e83409218879e7af293daa86b0c40eb015 Mon Sep 17 00:00:00 2001 From: Peng Date: Wed, 8 Jun 2016 15:22:07 +0800 Subject: [PATCH] Fix PANIC: metaslab_free_dva(): bad DVA X:Y:Z The following scenario can result in garbage in the dn_spill field. The db->db_blkptr must be set to NULL when DNODE_FLAG_SPILL_BLKPTR is clear to ensure the dn_spill field is cleared. Current txg = A. * A new spill buffer is created. Its dbuf is initialized with db_blkptr = NULL and it's dirtied. Current txg = B. * The spill buffer is modified. It's marked as dirty in this txg. * Additional changes make the spill buffer unnecessary because the xattr fits into the bonus buffer, so it's removed. The dbuf is undirtied in this txg, but it's still referenced and cannot be destroyed. Current txg = C. * Starts syncing of txg A * dbuf_sync_leaf() is called for the spill buffer. Since db_blkptr is NULL, dbuf_check_blkptr() is called. * The dbuf starts being written and it reaches the ready state (not done yet). * A new change makes the spill buffer necessary again. sa_build_layouts() ends up calling dbuf_find() to locate the dbuf. It finds the old dbuf because it has not been destroyed yet (it will be destroyed when the previous write is done and there are no more references). The old dbuf has db_blkptr != NULL. * txg A write is complete and the dbuf released. However it's still referenced, so it's not destroyed. Current txg = D. * Starts syncing of txg B * dbuf_sync_leaf() is called for the bonus buffer. Its contents are directly copied into the dnode, overwriting the blkptr area because, in txg B, the bonus buffer was big enough to hold the entire xattr. * At this point, the db_blkptr of the spill buffer used in txg C gets corrupted. Signed-off-by: Peng Signed-off-by: Tim Chase Signed-off-by: Brian Behlendorf Closes #3937 --- module/zfs/dbuf.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c index 4bbbd05253..61cc83e411 100644 --- a/module/zfs/dbuf.c +++ b/module/zfs/dbuf.c @@ -2943,6 +2943,22 @@ dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx) if (db->db_blkid == DMU_SPILL_BLKID) { mutex_enter(&dn->dn_mtx); + if (!(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR)) { + /* + * In the previous transaction group, the bonus buffer + * was entirely used to store the attributes for the + * dnode which overrode the dn_spill field. However, + * when adding more attributes to the file a spill + * block was required to hold the extra attributes. + * + * Make sure to clear the garbage left in the dn_spill + * field from the previous attributes in the bonus + * buffer. Otherwise, after writing out the spill + * block to the new allocated dva, it will free + * the old block pointed to by the invalid dn_spill. + */ + db->db_blkptr = NULL; + } dn->dn_phys->dn_flags |= DNODE_FLAG_SPILL_BLKPTR; mutex_exit(&dn->dn_mtx); }