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Illumos 5150 - zfs clone of a defer_destroy snapshot causes strangeness

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When a clone is created of a snapshot that has been marked for
deferred destroy (with "zfs destroy -d"), the clone "inherits" the
defer_destroy flag from the origin, and any snapshots of the clone
"inherit" the defer_destroy flag from the clone. This causes a strange
situation where the clone's snapshots are marked for defer_destroy but
they have no holds or clones. If the clone's snapshot gets a hold or
clone, which is then deleted, we will honor the incorrectly-set
defer_destroy flag and delete the snapshot!

Steps to reproduce:

  * zpool create test c1t1d0
  * zfs create test/fs
  * zfs snapshot test/fs@a
  * zfs clone test/fs@a test/clone
  * zfs destroy -d test/fs@a
  * zfs clone test/fs@a test/clone2
  * zfs snapshot test/clone2@a
  * zfs hold hld test/clone2@a
  * zfs release hld test/clone2@a
  * zfs list -r -t all test

  <test/clone2@a has been destroyed>

We noticed that this causes dcenter to get very confused, because it
treats snapshots that are marked defer_destroy as not existing. So it
won't see any snapshots of the clone that's marked defer_destroy.

5150 - zfs clone of a defer_destroy snapshot causes strangeness
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Robert Mustacchi <rm@joyent.com>

References:
  https://www.illumos.org/projects/illumos-gate//issues/5150
  https://github.com/illumos/illumos-gate/commit/42fcb65

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2690
This commit is contained in:
Matthew Ahrens 2014-09-12 05:45:50 +02:00 committed by Brian Behlendorf
parent 6c59307a3c
commit 4b20a6f509
1 changed files with 7 additions and 1 deletions
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8
module/zfs/dsl_dataset.c
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@ -686,7 +686,13 @@ dsl_dataset_create_sync_dd(dsl_dir_t *dd, dsl_dataset_t *origin,
dsphys->ds_uncompressed_bytes =
origin->ds_phys->ds_uncompressed_bytes;
dsphys->ds_bp = origin->ds_phys->ds_bp;
dsphys->ds_flags |= origin->ds_phys->ds_flags;
/*
* Inherit flags that describe the dataset's contents
* (INCONSISTENT) or properties (Case Insensitive).
*/
dsphys->ds_flags |= origin->ds_phys->ds_flags &
(DS_FLAG_INCONSISTENT | DS_FLAG_CI_DATASET);
dmu_buf_will_dirty(origin->ds_dbuf, tx);
origin->ds_phys->ds_num_children++;