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Fix core dump in ReorderBufferRestoreChange on alignment-picky platforms.
When re-reading an update involving both an old tuple and a new tuple from disk, reorderbuffer.c was careless about whether the new tuple is suitably aligned for direct access --- in general, it isn't. We'd missed seeing this in the buildfarm because the contrib/test_decoding tests exercise this code path only a few times, and by chance all of those cases have old tuples with length a multiple of 4, which is usually enough to make the access to the new tuple's t_len safe. For some still-not-entirely-clear reason, however, Debian's sparc build gets a bus error, as reported by Christoph Berg; perhaps it's assuming 8-byte alignment of the pointer? The lack of previous field reports is probably because you need all of these conditions to trigger a crash: an alignment-picky platform (not Intel), a transaction large enough to spill to disk, an update within that xact that changes a primary-key field and has an odd-length old tuple, and of course logical decoding tracing the transaction. Avoid the alignment assumption by using memcpy instead of fetching t_len directly, and add a test case that exposes the crash on picky platforms. Back-patch to 9.4 where the bug was introduced. Discussion: <20160413094117.GC21485@msg.credativ.de>
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@ -227,6 +227,8 @@ CREATE TABLE tr_etoomuch (id serial primary key, data int);
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INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
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DELETE FROM tr_etoomuch WHERE id < 5000;
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UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
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CREATE TABLE tr_oddlength (id text primary key, data text);
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INSERT INTO tr_oddlength VALUES('ab', 'foo');
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COMMIT;
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/* display results, but hide most of the output */
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SELECT count(*), min(data), max(data)
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@ -234,16 +236,19 @@ FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids',
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GROUP BY substring(data, 1, 24)
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ORDER BY 1,2;
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count | min | max
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-------+-------------------------------------------------+------------------------------------------------------------------------
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-------+-------------------------------------------------------------------+------------------------------------------------------------------------
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1 | BEGIN | BEGIN
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1 | COMMIT | COMMIT
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1 | table public.tr_oddlength: INSERT: id[text]:'ab' data[text]:'foo' | table public.tr_oddlength: INSERT: id[text]:'ab' data[text]:'foo'
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20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
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(3 rows)
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(4 rows)
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-- check updates of primary keys work correctly
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BEGIN;
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CREATE TABLE spoolme AS SELECT g.i FROM generate_series(1, 5000) g(i);
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UPDATE tr_etoomuch SET id = -id WHERE id = 5000;
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UPDATE tr_oddlength SET id = 'x', data = 'quux';
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UPDATE tr_oddlength SET id = 'yy', data = 'a';
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DELETE FROM spoolme;
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DROP TABLE spoolme;
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COMMIT;
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@ -253,7 +258,9 @@ WHERE data ~ 'UPDATE';
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data
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-------------------------------------------------------------------------------------------------------------
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table public.tr_etoomuch: UPDATE: old-key: id[integer]:5000 new-tuple: id[integer]:-5000 data[integer]:5000
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(1 row)
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table public.tr_oddlength: UPDATE: old-key: id[text]:'ab' new-tuple: id[text]:'x' data[text]:'quux'
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table public.tr_oddlength: UPDATE: old-key: id[text]:'x' new-tuple: id[text]:'yy' data[text]:'a'
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(3 rows)
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-- check that a large, spooled, upsert works
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INSERT INTO tr_etoomuch (id, data)
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@ -115,6 +115,8 @@ CREATE TABLE tr_etoomuch (id serial primary key, data int);
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INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
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DELETE FROM tr_etoomuch WHERE id < 5000;
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UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
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CREATE TABLE tr_oddlength (id text primary key, data text);
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INSERT INTO tr_oddlength VALUES('ab', 'foo');
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COMMIT;
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/* display results, but hide most of the output */
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@ -127,6 +129,8 @@ ORDER BY 1,2;
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BEGIN;
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CREATE TABLE spoolme AS SELECT g.i FROM generate_series(1, 5000) g(i);
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UPDATE tr_etoomuch SET id = -id WHERE id = 5000;
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UPDATE tr_oddlength SET id = 'x', data = 'quux';
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UPDATE tr_oddlength SET id = 'yy', data = 'a';
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DELETE FROM spoolme;
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DROP TABLE spoolme;
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COMMIT;
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@ -2347,6 +2347,10 @@ ReorderBufferRestoreChanges(ReorderBuffer *rb, ReorderBufferTXN *txn,
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/*
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* Convert change from its on-disk format to in-memory format and queue it onto
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* the TXN's ->changes list.
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*
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* Note: although "data" is declared char*, at entry it points to a
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* maxalign'd buffer, making it safe in most of this function to assume
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* that the pointed-to data is suitably aligned for direct access.
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*/
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static void
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ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
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@ -2374,7 +2378,7 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
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case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
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if (change->data.tp.oldtuple)
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{
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Size tuplelen = ((HeapTuple) data)->t_len;
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uint32 tuplelen = ((HeapTuple) data)->t_len;
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change->data.tp.oldtuple =
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ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
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@ -2395,7 +2399,11 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
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if (change->data.tp.newtuple)
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{
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Size tuplelen = ((HeapTuple) data)->t_len;
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/* here, data might not be suitably aligned! */
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uint32 tuplelen;
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memcpy(&tuplelen, data + offsetof(HeapTupleData, t_len),
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sizeof(uint32));
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change->data.tp.newtuple =
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ReorderBufferGetTupleBuf(rb, tuplelen - SizeofHeapTupleHeader);
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