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Replace RelationOpenSmgr() with RelationGetSmgr().

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The idea behind this patch is to design out bugs like the one fixed
by commit 9d523119f.  Previously, once one did RelationOpenSmgr(rel),
it was considered okay to access rel->rd_smgr directly for some
not-very-clear interval.  But since that pointer will be cleared by
relcache flushes, we had bugs arising from overreliance on a previous
RelationOpenSmgr call still being effective.

Now, very little code except that in rel.h and relcache.c should ever
touch the rd_smgr field directly.  The normal coding rule is to use
RelationGetSmgr(rel) and not expect the result to be valid for longer
than one smgr function call.  There are a couple of places where using
the function every single time seemed like overkill, but they are now
annotated with large warning comments.

Amul Sul, after an idea of mine.

Discussion: https://postgr.es/m/CANiYTQsU7yMFpQYnv=BrcRVqK_3U3mtAzAsJCaqtzsDHfsUbdQ@mail.gmail.com
This commit is contained in:
Tom Lane
2021-07-12 17:01:29 -04:00
parent 5b60cf35f5
commit f10f0ae420
21 changed files with 164 additions and 165 deletions
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4
contrib/pg_prewarm/autoprewarm.c
View File

@ -514,15 +514,13 @@ autoprewarm_database_main(Datum main_arg)
old_blk->filenode != blk->filenode ||
old_blk->forknum != blk->forknum)
{
RelationOpenSmgr(rel);
/*
* smgrexists is not safe for illegal forknum, hence check whether
* the passed forknum is valid before using it in smgrexists.
*/
if (blk->forknum > InvalidForkNumber &&
blk->forknum <= MAX_FORKNUM &&
smgrexists(rel->rd_smgr, blk->forknum))
smgrexists(RelationGetSmgr(rel), blk->forknum))
nblocks = RelationGetNumberOfBlocksInFork(rel, blk->forknum);
else
nblocks = 0;

5
contrib/pg_prewarm/pg_prewarm.c
View File

@ -109,8 +109,7 @@ pg_prewarm(PG_FUNCTION_ARGS)
aclcheck_error(aclresult, get_relkind_objtype(rel->rd_rel->relkind), get_rel_name(relOid));
/* Check that the fork exists. */
RelationOpenSmgr(rel);
if (!smgrexists(rel->rd_smgr, forkNumber))
if (!smgrexists(RelationGetSmgr(rel), forkNumber))
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("fork \"%s\" does not exist for this relation",
@ -178,7 +177,7 @@ pg_prewarm(PG_FUNCTION_ARGS)
for (block = first_block; block <= last_block; ++block)
{
CHECK_FOR_INTERRUPTS();
smgrread(rel->rd_smgr, forkNumber, block, blockbuffer.data);
smgrread(RelationGetSmgr(rel), forkNumber, block, blockbuffer.data);
++blocks_done;
}
}