NotificationsYou must be signed in to change notification settings
Fork6
Star31

Commitd5ee4db

committed

Use MAXALIGN() in calculations using sizeof(SlabBlock)

c6e0fe1 added a new pointer field to SlabBlock to make it 4 bytes largeron 32-bit machines. Prior to that commit, the size of that struct was amultiple of 8, which meant that MAXALIGN(sizeof(SlabBlock)) was the sameas sizeof(SlabBlock), however, afterc6e0fe1, due to the addition of thenew pointer field to store a pointer to the owning context, that was nolonger true on builds with sizeof(void *) == 4.This problem was highlighted by an Assert failure which was checking thatthe pointer given to pfree() was MAXALIGNED. Various 32-bit ARM buildfarmanimals were failing. These have MAXIMUM_ALIGNOF of 8. The only 32-bittesting I'd managed to do onc6e0fe1 had been on x86, which has aMAXIMUM_ALIGNOF of 4, therefore did not exhibit this issue.Here we define Slab_BLOCKHDRSZ and copy what is being done in aset.c andgeneration.c for doing calculations based on the size of the context'sblock type. This means that SlabAlloc() will now always return aMAXALIGNed pointer.This also fixes an incorrect sentinel_ok() check in SlabCheck() which wasincorrectly checking the wrong sentinel byte. This must have previouslynot caused any issues due to the fullChunkSize never being large enough tostore the sentinel byte.Diagnosed-by: Tomas Vondra, Tom LaneAuthor: Tomas Vondra, David RowleyDiscussion:https://postgr.es/m/CAA4eK1%2B1JyW5TiL%3DyV-3Uq1CrfnTyn0Xrk5uArt31Z%3D8rgPhXQ%40mail.gmail.com

1 parentb1ec7f4 commitd5ee4dbCopy full SHA for d5ee4db

File tree

1 file changed

-5

lines changed

src/backend/utils/mmgr
- slab.c

1 file changed

-5

lines changed

`‎src/backend/utils/mmgr/slab.c`

Lines changed: 7 additions & 5 deletions

Original file line number	Diff line number	Diff line change
`@@ -58,6 +58,8 @@`
`58`	`58`	`#include"utils/memutils_memorychunk.h"`
`59`	`59`	`#include"utils/memutils_internal.h"`
`60`	`60`
	`61`	`+#defineSlab_BLOCKHDRSZMAXALIGN(sizeof(SlabBlock))`
	`62`	`+`
`61`	`63`	`/*`
`62`	`64`	`* SlabContext is a specialized implementation of MemoryContext.`
`63`	`65`	`*/`
`@@ -102,10 +104,10 @@ typedef struct SlabBlock`
`102`	`104`	`#defineSlabChunkGetPointer(chk)\`
`103`	`105`	`((void )(((char )(chk)) + sizeof(MemoryChunk)))`
`104`	`106`	`#defineSlabBlockGetChunk(slab,block,idx) \`
`105`		`-((MemoryChunk ) ((char ) (block) +sizeof(SlabBlock)\`
	`107`	`+((MemoryChunk ) ((char ) (block) +Slab_BLOCKHDRSZ\`
`106`	`108`	`+ (idx * slab->fullChunkSize)))`
`107`	`109`	`#defineSlabBlockStart(block)\`
`108`		`-((char *) block +sizeof(SlabBlock))`
	`110`	`+((char *) block +Slab_BLOCKHDRSZ)`
`109`	`111`	`#defineSlabChunkIndex(slab,block,chunk)\`
`110`	`112`	`(((char *) chunk - SlabBlockStart(block)) / slab->fullChunkSize)`
`111`	`113`
`@@ -146,12 +148,12 @@ SlabContextCreate(MemoryContext parent,`
`146`	`148`	`fullChunkSize=Slab_CHUNKHDRSZ+MAXALIGN(chunkSize);`
`147`	`149`
`148`	`150`	`/* Make sure the block can store at least one chunk. */`
`149`		`-if (blockSize<fullChunkSize+sizeof(SlabBlock))`
	`151`	`+if (blockSize<fullChunkSize+Slab_BLOCKHDRSZ)`
`150`	`152`	`elog(ERROR,"block size %zu for slab is too small for %zu chunks",`
`151`	`153`	`blockSize,chunkSize);`
`152`	`154`
`153`	`155`	`/* Compute maximum number of chunks per block */`
`154`		`-chunksPerBlock= (blockSize-sizeof(SlabBlock)) /fullChunkSize;`
	`156`	`+chunksPerBlock= (blockSize-Slab_BLOCKHDRSZ) /fullChunkSize;`
`155`	`157`
`156`	`158`	`/* The freelist starts with 0, ends with chunksPerBlock. */`
`157`	`159`	`freelistSize=sizeof(dlist_head)* (chunksPerBlock+1);`
`@@ -744,7 +746,7 @@ SlabCheck(MemoryContext context)`
`744`	`746`
`745`	`747`	`/* there might be sentinel (thanks to alignment) */`
`746`	`748`	`if (slab->chunkSize< (slab->fullChunkSize-Slab_CHUNKHDRSZ))`
`747`		`-if (!sentinel_ok(chunk,slab->chunkSize))`
	`749`	`+if (!sentinel_ok(chunk,Slab_CHUNKHDRSZ+slab->chunkSize))`
`748`	`750`	`elog(WARNING,"problem in slab %s: detected write past chunk end in block %p, chunk %p",`
`749`	`751`	`name,block,chunk);`
`750`	`752`	`}`

0 commit comments

Comments

(0)

Movatterモバイル変換

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commitd5ee4db

File tree

1 file changed

1 file changed

`‎src/backend/utils/mmgr/slab.c`

0 commit comments