[ovs-dev] [PATCH v2 2/2] ovsdb-idl: Preserve references for deleted rows.

Ilya Maximets i.maximets at ovn.org
Tue Mar 9 16:56:08 UTC 2021


On 3/9/21 5:54 PM, Ilya Maximets wrote:
> On 3/9/21 5:26 PM, Dumitru Ceara wrote:
>> On 3/9/21 4:07 PM, Ilya Maximets wrote:
>>> On 3/3/21 3:40 PM, Dumitru Ceara wrote:
>>>> Considering two DB rows, 'a' from table A and 'b' from table B (with
>>>> column 'ref_a' a reference to table A):
>>>> a = {A._uuid=<U1>}
>>>> b = {B._uuid=<U2>, B.ref_a=<U1>}
>>>>
>>>> Assuming both records are present in the IDL client's in-memory view of
>>>> the database, depending whether row 'b' is also deleted in the same
>>>> transaction or not, deletion of row 'a' should generate the following
>>>> tracked changes:
>>>>
>>>> 1. only row 'a' is deleted:
>>>> - for table A:
>>>>    - deleted records: a = {A._uuid=<U1>}
>>>> - for table B:
>>>>    - updated records: b = {B._uuid=<U2>, B.ref_a=[]}
>>>>
>>>> 2. row 'a' and row 'b' are deleted in the same update:
>>>> - for table A:
>>>>    - deleted records: a = {A._uuid=<U1>}
>>>> - for table B:
>>>>    - deleted records: b = {B._uuid=<U2>, B.ref_a=<U1>}
>>>>
>>>> To ensure this, we now delay reparsing row backrefs until the row has
>>>> been removed from the table's hmap and until the IDL client has
>>>> processed all tracked changes (ovsdb_idl_track_clear() was called).
>>>>
>>>> Without this change, in scenario 2 above, the tracked changes for table
>>>> B would be:
>>>> - deleted records: b = {B._uuid=<U2>, B.ref_a=[]}
>>>>
>>>> In particular, for strong references, row 'a' can never be deleted in
>>>> a transaction that happens strictly before row 'b' is deleted.  In some
>>>> cases [0] both rows are deleted in the same transaction and having
>>>> B.ref_a=[] would violate the integrity of the database from client
>>>> perspective.  This would force the client to always validate that
>>>> strong reference fields are non-NULL.  This is not really an option
>>>> because the information in the original reference is required for
>>>> incrementally processing the record deletion.
>>>>
>>>> [0] with ovn-monitor-all=true, the following command triggers a crash
>>>>      in ovn-controller because a strong reference field becomes NULL:
>>>>      $ ovn-nbctl --wait=hv -- lr-add r -- lrp-add r rp 00:00:00:00:00:01 1.0.0.1/24
>>>>      $ ovn-nbctl lr-del r
>>>>
>>>> Reported-at: https://bugzilla.redhat.com/1932642
>>>> Fixes: 72aeb243a52a ("ovsdb-idl: Tracking - preserve data for deleted rows.")
>>>> Signed-off-by: Dumitru Ceara <dceara at redhat.com>
>>>> ---
>>>> v2:
>>>>    - Added ovsdb-idl.at test for strong references.
>>>> ---
>>>>   lib/ovsdb-idl.c    |    6 ++-
>>>>   tests/ovsdb-idl.at |  118 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>   tests/test-ovsdb.c |   45 ++++++++++++++++++++
>>>>   3 files changed, 167 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/lib/ovsdb-idl.c b/lib/ovsdb-idl.c
>>>> index 9e1e787..ecd4924 100644
>>>> --- a/lib/ovsdb-idl.c
>>>> +++ b/lib/ovsdb-idl.c
>>>> @@ -163,6 +163,7 @@ static void ovsdb_idl_row_unparse(struct ovsdb_idl_row *);
>>>>   static void ovsdb_idl_row_clear_old(struct ovsdb_idl_row *);
>>>>   static void ovsdb_idl_row_clear_new(struct ovsdb_idl_row *);
>>>>   static void ovsdb_idl_row_clear_arcs(struct ovsdb_idl_row *, bool destroy_dsts);
>>>> +static void ovsdb_idl_row_reparse_backrefs(struct ovsdb_idl_row *row);
>>>>     static void ovsdb_idl_txn_abort_all(struct ovsdb_idl *);
>>>>   static bool ovsdb_idl_txn_extract_mutations(struct ovsdb_idl_row *,
>>>> @@ -367,6 +368,8 @@ ovsdb_idl_clear(struct ovsdb_idl *db)
>>>>                   ovsdb_idl_row_unparse(row);
>>>>               }
>>>>               LIST_FOR_EACH_SAFE (arc, next_arc, src_node, &row->src_arcs) {
>>>> +                ovs_list_remove(&arc->src_node);
>>>> +                ovs_list_remove(&arc->dst_node);
>>>>                   free(arc);
>>>>               }
>>>>               /* No need to do anything with dst_arcs: some node has those arcs
>>>> @@ -1234,6 +1237,7 @@ ovsdb_idl_track_clear__(struct ovsdb_idl *idl, bool flush_all)
>>>>                   ovs_list_remove(&row->track_node);
>>>>                   ovs_list_init(&row->track_node);
>>>>                   if (ovsdb_idl_row_is_orphan(row)) {
>>>> +                    ovsdb_idl_row_reparse_backrefs(row);
>>>>                       ovsdb_idl_row_unparse(row);
>>>>                       if (row->tracked_old_datum) {
>>>>                           const struct ovsdb_idl_table_class *class =
>>>> @@ -2156,8 +2160,6 @@ ovsdb_idl_delete_row(struct ovsdb_idl_row *row)
>>>>       ovsdb_idl_row_clear_old(row);
>>>>       if (ovs_list_is_empty(&row->dst_arcs)) {
>>>>           ovsdb_idl_row_destroy(row);
>>>> -    } else {
>>>> -        ovsdb_idl_row_reparse_backrefs(row);
>>>>       }
>>>
>>> By removing the ovsdb_idl_row_reparse_backrefs() you're making an assumption
>>> that we always have a modification event for all rows that are referencing
>>> this one.  But that is not always the case.
>>>
>>> There is scenario where this re-parsing is needed.  In short, if you're
>>> reducing the scope of conditional monitoring and some rows becomes
>>> orphan rows.  In this case ovsdb-server will not generate 'modify' event
>>> for the row that references our newly orphan row, so it will not be
>>> re-parsed and these orphan rows will be accessible the row that references
>>> them.
>>
>> You're right, thanks for spotting this and for the test case.
>>
>>>
>>> Here is a quick'n'dirty testcase, how to reproduce:
>>> diff --git a/tests/ovsdb-idl.at b/tests/ovsdb-idl.at
>>> index 702502280..c6bb3f348 100644
>>> --- a/tests/ovsdb-idl.at
>>> +++ b/tests/ovsdb-idl.at
>>> @@ -1174,7 +1174,7 @@ OVSDB_CHECK_IDL_TRACK([track, simple idl, initially populated],
>>>   dnl This test creates database with weak references and checks that orphan
>>>   dnl rows created for weak references are not available for iteration via
>>>   dnl list of tracked changes.
>>> -OVSDB_CHECK_IDL_TRACK([track, simple idl, initially populated, orphan weak references],
>>> +OVSDB_CHECK_IDL_TRACK([track, simple idl, initially populated, orphan weak references quickndirty],
>>>     [['["idltest",
>>>         {"op": "insert",
>>>          "table": "simple",
>>> @@ -1196,7 +1196,7 @@ OVSDB_CHECK_IDL_TRACK([track, simple idl, initially populated, orphan weak refer
>>>                                 ["named-uuid", "weak_row1"],
>>>                                 ["named-uuid", "weak_row2"]]
>>>                              ]}}]']],
>>> -  [['condition simple []' \
>>> +  [['condition simple [true]' \
>>>       'condition simple [["s","==","row1_s"]]' \
>>>       '["idltest",
>>>         {"op": "update",
>>> diff --git a/tests/test-ovsdb.c b/tests/test-ovsdb.c
>>> index 36fb9cc08..ace87b13d 100644
>>> --- a/tests/test-ovsdb.c
>>> +++ b/tests/test-ovsdb.c
>>> @@ -2157,6 +2157,7 @@ print_idl_row_singleton(const struct idltest_singleton *sng, int step)
>>>   static void
>>>   print_idl(struct ovsdb_idl *idl, int step)
>>>   {
>>> +    const struct idltest_simple6 *s6;
>>>       const struct idltest_simple *s;
>>>       const struct idltest_link1 *l1;
>>>       const struct idltest_link2 *l2;
>>> @@ -2175,6 +2176,10 @@ print_idl(struct ovsdb_idl *idl, int step)
>>>           print_idl_row_link2(l2, step);
>>>           n++;
>>>       }
>>> +    IDLTEST_SIMPLE6_FOR_EACH (s6, idl) {
>>> +        print_idl_row_simple6(s6, step);
>>> +        n++;
>>> +    }
>>>       IDLTEST_SINGLETON_FOR_EACH (sng, idl) {
>>>           print_idl_row_singleton(sng, step);
>>>           n++;
>>> @@ -2638,8 +2643,12 @@ do_idl(struct ovs_cmdl_context *ctx)
>>>                 /* Print update. */
>>>               if (track) {
>>> -                print_idl_track(idl, step++);
>>> +                print_idl_track(idl, step);
>>> +                print_and_log("%03d: print_idl[1]", step);
>>> +                print_idl(idl, step);
>>>                   ovsdb_idl_track_clear(idl);
>>> +                print_and_log("%03d: print_idl[2]", step);
>>> +                print_idl(idl, step++);
>>>               } else {
>>>                   print_idl(idl, step++);
>>>               }
>>> ---
>>>
>>> By running make -j8 check TESTSUITEFLAGS='-k quickndirty -v', you will have
>>> some output for the commands in the log.
>>>
>>>
>>> The first condition for a 'simple' table is 'true', so we will receive all
>>> 3 rows from this table and also row from the 'simple6'.
>>> All 3 rows are in a weak references:
>>>
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row0_s <> uuid=2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row2_s <> uuid=1fd88ded-06f0-4fee-a21b-4e552d8a2f50
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row1_s <> uuid=124ddccb-7eb8-4def-b768-887cb8d84ada
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple6: inserted row: name=first_row weak_ref=[124ddccb-7eb8-4def-b768-887cb8d84ada 1fd88ded-06f0-4fee-a21b-4e552d8a2f50 2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0]
>>> test-ovsdb|test_ovsdb|001: table simple6: updated columns: name weak_ref
>>>
>>>
>>> All of them are accessible for a user before the track_clear():
>>>
>>> test-ovsdb|test_ovsdb|001: print_idl[1]
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row0_s <> uuid=2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row2_s <> uuid=1fd88ded-06f0-4fee-a21b-4e552d8a2f50
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row1_s <> uuid=124ddccb-7eb8-4def-b768-887cb8d84ada
>>> test-ovsdb|test_ovsdb|001: table simple: updated columns: s
>>> test-ovsdb|test_ovsdb|001: table simple6: inserted row: name=first_row weak_ref=[124ddccb-7eb8-4def-b768-887cb8d84ada 1fd88ded-06f0-4fee-a21b-4e552d8a2f50 2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0]
>>> test-ovsdb|test_ovsdb|001: table simple6: updated columns: name weak_ref
>>>
>>> And after:
>>>
>>> test-ovsdb|test_ovsdb|001: print_idl[2]
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row0_s <> uuid=2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row2_s <> uuid=1fd88ded-06f0-4fee-a21b-4e552d8a2f50
>>> test-ovsdb|test_ovsdb|001: table simple: inserted row: s=row1_s <> uuid=124ddccb-7eb8-4def-b768-887cb8d84ada
>>> test-ovsdb|test_ovsdb|001: table simple6: name=first_row weak_ref=[124ddccb-7eb8-4def-b768-887cb8d84ada 1fd88ded-06f0-4fee-a21b-4e552d8a2f50 2309fce8-a6dd-46e5-a603-fe1ea1ab6bb0]
>>>
>>>
>>> Now condition is changed.  This makes 2 of 3 rows to become orphan rows.
>>> Note that the update notification only removes orphan rows, but doesn't
>>> modify the row in simple6, because rows wasn't actually removed, just
>>> not needed anymore:
>>>
>>> test-ovsdb|jsonrpc|unix:socket: send request, method="monitor_cond_change", params=[["monid","idltest"],["monid","idltest"],{"simple":[{"where":[["s","==","row1_s"]]}]}], id=5
>>> test-ovsdb|jsonrpc|unix:socket: received notification, method="update3", params=[["monid","idltest"],"00000000-0000-0000-0000-000000000000",{"simple":{"3aa79e4a-d752-4d53-8e16-b62887d73ad8":{"delete":null},"d1b023f3-3b4d-4bb5-b4d9-cc9791afde7a":{"delete":null}}}]
>>> test-ovsdb|jsonrpc|unix:socket: received reply, result={}, id=5
>>>
>>> Track list is empty, but 2 orphan rows should be on a track list as deleted:
>>
>> This actually uncovers a new potential issue: the 2 orphan rows are not on the tracked list even without my change.  That's because ovsdb_idl_row_destroy() doesn't get called if the row becomes orphan so it won't be added to 'row->table->track_list'.
> 
> Hmm.  Thanks for sponning that.

*spotting

> 
> On current master these 2 rows appears on a tracked list only after
> occasional unrelated modification of a row in 'simple6' and that is
> not good:
> 
> test-ovsdb|test_ovsdb|002: change conditions
> test-ovsdb|jsonrpc|unix:socket: send request, method="monitor_cond_change", params=[["monid","idltest"],["monid","idltest"],{"simple":[{"where":[["s","==","row1_s"]]}]}], id=5
> test-ovsdb|jsonrpc|unix:socket: received notification, method="update3", params=[["monid","idltest"],"00000000-0000-0000-0000-000000000000",{"simple":{"0f94ec57-2fc2-4a70-a0cf-b96b11fe0d78":{"delete":null},"5a1d0257-fc27-4046-9e18-25539f122052":{"delete":null}}}]
> test-ovsdb|jsonrpc|unix:socket: received reply, result={}, id=5
> test-ovsdb|test_ovsdb|003: empty
> test-ovsdb|test_ovsdb|003: print_idl[1]
> test-ovsdb|test_ovsdb|003: table simple: s=row1_s uuid=77db422f-042f-4e1f-9a40-6487e5cdd3ae
> test-ovsdb|test_ovsdb|003: table simple6: name=first_row weak_ref=[77db422f-042f-4e1f-9a40-6487e5cdd3ae]
> test-ovsdb|test_ovsdb|003: print_idl[2]
> test-ovsdb|test_ovsdb|003: table simple: s=row1_s uuid=77db422f-042f-4e1f-9a40-6487e5cdd3ae
> test-ovsdb|test_ovsdb|003: table simple6: name=first_row weak_ref=[77db422f-042f-4e1f-9a40-6487e5cdd3ae]
> 
> test-ovsdb|jsonrpc|unix:socket: send request, method="transact", params=["idltest",{"where":[],"row":{"name":"new_name"},"op":"update","table":"simple6"}], id=6
> test-ovsdb|jsonrpc|unix:socket: received reply, result=[{"count":1}], id=6
> test-ovsdb|test_ovsdb|004: {"error":null,"result":[{"count":1}]}
> test-ovsdb|jsonrpc|unix:socket: received notification, method="update3", params=[["monid","idltest"],"00000000-0000-0000-0000-000000000000",{"simple6":{"618cef34-e635-4841-9dc7-a14eb2b9627e":{"modify":{"name":"new_name"}}}}]
> test-ovsdb|test_ovsdb|005: table simple: deleted row: s=row2_s uuid=5a1d0257-fc27-4046-9e18-25539f122052
> test-ovsdb|test_ovsdb|005: table simple: deleted row: s=row0_s uuid=0f94ec57-2fc2-4a70-a0cf-b96b11fe0d78
> test-ovsdb|test_ovsdb|005: table simple6: name=new_name weak_ref=[77db422f-042f-4e1f-9a40-6487e5cdd3ae]
> test-ovsdb|test_ovsdb|005: table simple6: updated columns: name
> 
> 
> It's probably because ovsdb_idl_row_reparse_backrefs() calls
> ovsdb_idl_row_clear_arcs() with destroy_dsts=false.  So, re-parsing
> invoked for two deleted rows doesn't actually destroy them.
> 
>>
>>>
>>> test-ovsdb|test_ovsdb|003: empty
>>>
>>> But all 3 rows are still accessible for a user from the row in 'simple6' even
>>> though table 'simple' has only 1 row accessible:
>>>
>>> test-ovsdb|test_ovsdb|003: print_idl[1]
>>> test-ovsdb|test_ovsdb|003: table simple: s=row1_s <> uuid=b8315694-7855-43e7-a963-ca9a8666682a
>>> test-ovsdb|test_ovsdb|003: table simple6: name=first_row weak_ref=[3aa79e4a-d752-4d53-8e16-b62887d73ad8 b8315694-7855-43e7-a963-ca9a8666682a d1b023f3-3b4d-4bb5-b4d9-cc9791afde7a]
>>>
>>> And they are still here after the track_clear():
>>>
>>> test-ovsdb|test_ovsdb|003: print_idl[2]
>>> test-ovsdb|test_ovsdb|003: table simple: s=row1_s <> uuid=b8315694-7855-43e7-a963-ca9a8666682a
>>> test-ovsdb|test_ovsdb|003: table simple6: name=first_row weak_ref=[3aa79e4a-d752-4d53-8e16-b62887d73ad8 b8315694-7855-43e7-a963-ca9a8666682a d1b023f3-3b4d-4bb5-b4d9-cc9791afde7a]
>>>
>>>
>>> When we have unrelated update on a row in 'simple6' it finally gets
>>> re-parsed and we have tracked orphan rows as deleted and they are
>>> no longer accessible for a user from a row in 'simple6':
>>>
>>> test-ovsdb|jsonrpc|unix:socket: received notification, method="update3", params=[["monid","idltest"],"00000000-0000-0000-0000-000000000000",{"simple6":{"6fcb8599-4161-4314-901c-2ca4a18686c3":{"modify":{"name":"new_name"}}}}]
>>>
>>> Tracked:
>>>
>>> test-ovsdb|test_ovsdb|005: table simple: deleted row: s=row0_s <> uuid=d1b023f3-3b4d-4bb5-b4d9-cc9791afde7a
>>> test-ovsdb|test_ovsdb|005: table simple: deleted row: s=row2_s <> uuid=3aa79e4a-d752-4d53-8e16-b62887d73ad8
>>> test-ovsdb|test_ovsdb|005: table simple6: name=new_name weak_ref=[b8315694-7855-43e7-a963-ca9a8666682a]
>>> test-ovsdb|test_ovsdb|005: table simple6: updated columns: name
>>>
>>> Before track_clear():
>>>
>>> test-ovsdb|test_ovsdb|005: print_idl[1]
>>> test-ovsdb|test_ovsdb|005: table simple: s=row1_s <> uuid=b8315694-7855-43e7-a963-ca9a8666682a
>>> test-ovsdb|test_ovsdb|005: table simple6: name=new_name weak_ref=[b8315694-7855-43e7-a963-ca9a8666682a]
>>> test-ovsdb|test_ovsdb|005: table simple6: updated columns: name
>>>
>>> After:
>>>
>>> test-ovsdb|test_ovsdb|005: print_idl[2]
>>> test-ovsdb|test_ovsdb|005: table simple: s=row1_s <> uuid=b8315694-7855-43e7-a963-ca9a8666682a
>>> test-ovsdb|test_ovsdb|005: table simple6: name=new_name weak_ref=[b8315694-7855-43e7-a963-ca9a8666682a]
>>>
>>
>> To cover all cases above I'm thinking of the following approach:
>>
>> 1. Delay ovsdb_idl_row_reparse_backrefs() for deleted rows until ovsdb_idl_parse_update() has finished.
>>
>> 2. After ovsdb_idl_parse_update(), walk all deleted rows and reparse backrefs but only for src rows that have not been deleted.
>>
>> 3. IDL user (e.g., ovn-controller) processes tracked changes.  At this point:
>> - non-deleted src rows with a weak reference to orphaned dst rows have ref == NULL.
>> - deleted src rows with a weak/strong reference to orphaned dst rows have ref != NULL but that's fine because they'll both be cleaned up at the next step below.
>>
>> 4. ovsdb_idl_track_clear()
>>
>> What do you think?
> 
> Sounds OK.  I'm not sure how the implementation should look like, though.
> Will this also fix the issue with not reacking deleted orphaned rows right away?
> 
>>
>>>
>>> Best regards, Ilya Maximets.
>>>
>>
>> Thanks,
>> Dumitru
>>
> 



More information about the dev mailing list