Make smgr access for a BufferManagerRelation safer in relcache inval

Currently there's no bug, because we have no code path where we
invalidate relcache entries where it'd cause a problem.  But it's more
robust to do it this way in case we introduce such a path later, as some
Postgres forks reportedly already have.

Author: Daniil Davydov <3danissimo@gmail.com>
Reviewed-by: Stepan Neretin <slpmcf@gmail.com>
Discussion: https://postgr.es/m/CAJDiXgj3FNzAhV+jjPqxMs3jz=OgPohsoXFj_fh-L+nS+13CKQ@mail.gmail.com

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index edf17ce3ea14fe46fad38a3cb468d82355c75016..e8544acb7841d86ae577ea032964680e192dc52e 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -883,14 +883,11 @@ ExtendBufferedRelBy(BufferManagerRelation bmr,
                                        uint32 *extended_by)
 {
        Assert((bmr.rel != NULL) != (bmr.smgr != NULL));
-       Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
+       Assert(bmr.smgr == NULL || bmr.relpersistence != '\0');
        Assert(extend_by > 0);
 
-       if (bmr.smgr == NULL)
-       {
-               bmr.smgr = RelationGetSmgr(bmr.rel);
+       if (bmr.relpersistence == '\0')
                bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
-       }
 
        return ExtendBufferedRelCommon(bmr, fork, strategy, flags,
                                                                   extend_by, InvalidBlockNumber,
@@ -919,14 +916,11 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
        Buffer          buffers[64];
 
        Assert((bmr.rel != NULL) != (bmr.smgr != NULL));
-       Assert(bmr.smgr == NULL || bmr.relpersistence != 0);
+       Assert(bmr.smgr == NULL || bmr.relpersistence != '\0');
        Assert(extend_to != InvalidBlockNumber && extend_to > 0);
 
-       if (bmr.smgr == NULL)
-       {
-               bmr.smgr = RelationGetSmgr(bmr.rel);
+       if (bmr.relpersistence == '\0')
                bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
-       }
 
        /*
         * If desired, create the file if it doesn't exist.  If
@@ -934,15 +928,15 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
         * an smgrexists call.
         */
        if ((flags & EB_CREATE_FORK_IF_NEEDED) &&
-               (bmr.smgr->smgr_cached_nblocks[fork] == 0 ||
-                bmr.smgr->smgr_cached_nblocks[fork] == InvalidBlockNumber) &&
-               !smgrexists(bmr.smgr, fork))
+               (BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] == 0 ||
+                BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] == InvalidBlockNumber) &&
+               !smgrexists(BMR_GET_SMGR(bmr), fork))
        {
                LockRelationForExtension(bmr.rel, ExclusiveLock);
 
                /* recheck, fork might have been created concurrently */
-               if (!smgrexists(bmr.smgr, fork))
-                       smgrcreate(bmr.smgr, fork, flags & EB_PERFORMING_RECOVERY);
+               if (!smgrexists(BMR_GET_SMGR(bmr), fork))
+                       smgrcreate(BMR_GET_SMGR(bmr), fork, flags & EB_PERFORMING_RECOVERY);
 
                UnlockRelationForExtension(bmr.rel, ExclusiveLock);
        }
@@ -952,13 +946,13 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
         * kernel.
         */
        if (flags & EB_CLEAR_SIZE_CACHE)
-               bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
+               BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] = InvalidBlockNumber;
 
        /*
         * Estimate how many pages we'll need to extend by. This avoids acquiring
         * unnecessarily many victim buffers.
         */
-       current_size = smgrnblocks(bmr.smgr, fork);
+       current_size = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
        /*
         * Since no-one else can be looking at the page contents yet, there is no
@@ -1002,7 +996,7 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
        if (buffer == InvalidBuffer)
        {
                Assert(extended_by == 0);
-               buffer = ReadBuffer_common(bmr.rel, bmr.smgr, bmr.relpersistence,
+               buffer = ReadBuffer_common(bmr.rel, BMR_GET_SMGR(bmr), bmr.relpersistence,
                                                                   fork, extend_to - 1, mode, strategy);
        }
 
@@ -2540,10 +2534,10 @@ ExtendBufferedRelCommon(BufferManagerRelation bmr,
        BlockNumber first_block;
 
        TRACE_POSTGRESQL_BUFFER_EXTEND_START(fork,
-                                                                                bmr.smgr->smgr_rlocator.locator.spcOid,
-                                                                                bmr.smgr->smgr_rlocator.locator.dbOid,
-                                                                                bmr.smgr->smgr_rlocator.locator.relNumber,
-                                                                                bmr.smgr->smgr_rlocator.backend,
+                                                                                BMR_GET_SMGR(bmr)->smgr_rlocator.locator.spcOid,
+                                                                                BMR_GET_SMGR(bmr)->smgr_rlocator.locator.dbOid,
+                                                                                BMR_GET_SMGR(bmr)->smgr_rlocator.locator.relNumber,
+                                                                                BMR_GET_SMGR(bmr)->smgr_rlocator.backend,
                                                                                 extend_by);
 
        if (bmr.relpersistence == RELPERSISTENCE_TEMP)
@@ -2557,10 +2551,10 @@ ExtendBufferedRelCommon(BufferManagerRelation bmr,
        *extended_by = extend_by;
 
        TRACE_POSTGRESQL_BUFFER_EXTEND_DONE(fork,
-                                                                               bmr.smgr->smgr_rlocator.locator.spcOid,
-                                                                               bmr.smgr->smgr_rlocator.locator.dbOid,
-                                                                               bmr.smgr->smgr_rlocator.locator.relNumber,
-                                                                               bmr.smgr->smgr_rlocator.backend,
+                                                                               BMR_GET_SMGR(bmr)->smgr_rlocator.locator.spcOid,
+                                                                               BMR_GET_SMGR(bmr)->smgr_rlocator.locator.dbOid,
+                                                                               BMR_GET_SMGR(bmr)->smgr_rlocator.locator.relNumber,
+                                                                               BMR_GET_SMGR(bmr)->smgr_rlocator.backend,
                                                                                *extended_by,
                                                                                first_block);
 
@@ -2626,9 +2620,9 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
         * kernel.
         */
        if (flags & EB_CLEAR_SIZE_CACHE)
-               bmr.smgr->smgr_cached_nblocks[fork] = InvalidBlockNumber;
+               BMR_GET_SMGR(bmr)->smgr_cached_nblocks[fork] = InvalidBlockNumber;
 
-       first_block = smgrnblocks(bmr.smgr, fork);
+       first_block = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
        /*
         * Now that we have the accurate relation size, check if the caller wants
@@ -2666,7 +2660,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
                ereport(ERROR,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg("cannot extend relation %s beyond %u blocks",
-                                               relpath(bmr.smgr->smgr_rlocator, fork).str,
+                                               relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str,
                                                MaxBlockNumber)));
 
        /*
@@ -2688,7 +2682,8 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
                ResourceOwnerEnlarge(CurrentResourceOwner);
                ReservePrivateRefCountEntry();
 
-               InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
+               InitBufferTag(&tag, &BMR_GET_SMGR(bmr)->smgr_rlocator.locator, fork,
+                                         first_block + i);
                hash = BufTableHashCode(&tag);
                partition_lock = BufMappingPartitionLock(hash);
 
@@ -2730,7 +2725,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
                                ereport(ERROR,
                                                (errmsg("unexpected data beyond EOF in block %u of relation \"%s\"",
                                                                existing_hdr->tag.blockNum,
-                                                               relpath(bmr.smgr->smgr_rlocator, fork).str)));
+                                                               relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str)));
 
                        /*
                         * We *must* do smgr[zero]extend before succeeding, else the page
@@ -2787,7 +2782,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
         *
         * We don't need to set checksum for all-zero pages.
         */
-       smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
+       smgrzeroextend(BMR_GET_SMGR(bmr), fork, first_block, extend_by, false);
 
        /*
         * Release the file-extension lock; it's now OK for someone else to extend

diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 04fef13409b029e9c3e945354360b016f978c6ef..15aac7d1c9fe47c1ceff345a078d6c9960b72353 100644 (file)
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -25,6 +25,7 @@
 #include "utils/guc_hooks.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
+#include "utils/rel.h"
 #include "utils/resowner.h"
 
 
@@ -372,7 +373,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
                MemSet(buf_block, 0, BLCKSZ);
        }
 
-       first_block = smgrnblocks(bmr.smgr, fork);
+       first_block = smgrnblocks(BMR_GET_SMGR(bmr), fork);
 
        if (extend_upto != InvalidBlockNumber)
        {
@@ -391,7 +392,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
                ereport(ERROR,
                                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                                 errmsg("cannot extend relation %s beyond %u blocks",
-                                               relpath(bmr.smgr->smgr_rlocator, fork).str,
+                                               relpath(BMR_GET_SMGR(bmr)->smgr_rlocator, fork).str,
                                                MaxBlockNumber)));
 
        for (uint32 i = 0; i < extend_by; i++)
@@ -408,7 +409,8 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
                /* in case we need to pin an existing buffer below */
                ResourceOwnerEnlarge(CurrentResourceOwner);
 
-               InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
+               InitBufferTag(&tag, &BMR_GET_SMGR(bmr)->smgr_rlocator.locator, fork,
+                                         first_block + i);
 
                hresult = (LocalBufferLookupEnt *)
                        hash_search(LocalBufHash, &tag, HASH_ENTER, &found);
@@ -456,7 +458,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
        io_start = pgstat_prepare_io_time(track_io_timing);
 
        /* actually extend relation */
-       smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
+       smgrzeroextend(BMR_GET_SMGR(bmr), fork, first_block, extend_by, false);
 
        pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL, IOOP_EXTEND,
                                                        io_start, 1, extend_by * BLCKSZ);

diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 3f37b294af64371d98f69245b83df7842cd738d1..b5f8f3c5d42f1ba36337b6651c3bc29bf2850ff9 100644 (file)
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -98,8 +98,11 @@ typedef struct SMgrRelationData *SMgrRelation;
 
 /*
  * Some functions identify relations either by relation or smgr +
- * relpersistence.  Used via the BMR_REL()/BMR_SMGR() macros below.  This
- * allows us to use the same function for both recovery and normal operation.
+ * relpersistence, initialized via the BMR_REL()/BMR_SMGR() macros below.
+ * This allows us to use the same function for both recovery and normal
+ * operation.  When BMR_REL is used, it's not valid to cache its rd_smgr here,
+ * because our pointer would be obsolete in case of relcache invalidation.
+ * For simplicity, use BMR_GET_SMGR to read the smgr.
  */
 typedef struct BufferManagerRelation
 {
@@ -108,8 +111,12 @@ typedef struct BufferManagerRelation
        char            relpersistence;
 } BufferManagerRelation;
 
-#define BMR_REL(p_rel) ((BufferManagerRelation){.rel = p_rel})
-#define BMR_SMGR(p_smgr, p_relpersistence) ((BufferManagerRelation){.smgr = p_smgr, .relpersistence = p_relpersistence})
+#define BMR_REL(p_rel) \
+       ((BufferManagerRelation){.rel = p_rel})
+#define BMR_SMGR(p_smgr, p_relpersistence) \
+       ((BufferManagerRelation){.smgr = p_smgr, .relpersistence = p_relpersistence})
+#define BMR_GET_SMGR(bmr) \
+       (RelationIsValid((bmr).rel) ? RelationGetSmgr((bmr).rel) : (bmr).smgr)
 
 /* Zero out page if reading fails. */
 #define READ_BUFFERS_ZERO_ON_ERROR (1 << 0)