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

Dumitru Ceara dceara at redhat.com
Tue Mar 9 16:26:25 UTC 2021


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'.

> 
> 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?

> 
> Best regards, Ilya Maximets.
> 

Thanks,
Dumitru



More information about the dev mailing list