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Add an experimental fix to avoid attempting to mmap memory from an offset that is not a multiple of the system page size on systems with page sizes larger than 32KB.

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FossilOrigin-Name: 6f3a5c24d254fc6faf607b505bdef4a7aafc21af
This commit is contained in:
dan
2014-03-20 08:59:47 +00:00
parent 344510e62b
commit 781e34cde3
3 changed files with 60 additions and 28 deletions
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71
src/os_unix.c
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@@ -4105,6 +4105,33 @@ static int unixShmSystemLock(
return rc;
}
/*
** Return the system page size.
*/
static int unixGetPagesize(void){
#if defined(_BSD_SOURCE)
return getpagesize();
#else
return (int)sysconf(_SC_PAGESIZE);
#endif
}
/*
** Return the minimum number of 32KB shm regions that should be mapped at
** a time, assuming that each mapping must be an integer multiple of the
** current system page-size.
**
** Usually, this is 1. The exception seems to be systems that are configured
** to use 64KB pages - in this case each mapping must cover at least two
** shm regions.
*/
static int unixShmRegionPerMap(void){
int shmsz = 32*1024; /* SHM region size */
int pgsz = unixGetPagesize(); /* System page size */
assert( ((pgsz-1)&pgsz)==0 ); /* Page size must be a power of 2 */
if( pgsz<shmsz ) return 1;
return pgsz/shmsz;
}
/*
** Purge the unixShmNodeList list of all entries with unixShmNode.nRef==0.
@@ -4116,10 +4143,11 @@ static void unixShmPurge(unixFile *pFd){
unixShmNode *p = pFd->pInode->pShmNode;
assert( unixMutexHeld() );
if( p && p->nRef==0 ){
int nShmPerMap = unixShmRegionPerMap();
int i;
assert( p->pInode==pFd->pInode );
sqlite3_mutex_free(p->mutex);
for(i=0; i<p->nRegion; i++){
for(i=0; i<p->nRegion; i+=nShmPerMap){
if( p->h>=0 ){
osMunmap(p->apRegion[i], p->szRegion);
}else{
@@ -4326,6 +4354,8 @@ static int unixShmMap(
unixShm *p;
unixShmNode *pShmNode;
int rc = SQLITE_OK;
int nShmPerMap = unixShmRegionPerMap();
int nReqRegion;
/* If the shared-memory file has not yet been opened, open it now. */
if( pDbFd->pShm==0 ){
@@ -4341,9 +4371,12 @@ static int unixShmMap(
assert( pShmNode->h>=0 || pDbFd->pInode->bProcessLock==1 );
assert( pShmNode->h<0 || pDbFd->pInode->bProcessLock==0 );
if( pShmNode->nRegion<=iRegion ){
/* Minimum number of regions required to be mapped. */
nReqRegion = ((iRegion+nShmPerMap) / nShmPerMap) * nShmPerMap;
if( pShmNode->nRegion<nReqRegion ){
char **apNew; /* New apRegion[] array */
int nByte = (iRegion+1)*szRegion; /* Minimum required file size */
int nByte = nReqRegion*szRegion; /* Minimum required file size */
struct stat sStat; /* Used by fstat() */
pShmNode->szRegion = szRegion;
@@ -4392,17 +4425,19 @@ static int unixShmMap(
/* Map the requested memory region into this processes address space. */
apNew = (char **)sqlite3_realloc(
pShmNode->apRegion, (iRegion+1)*sizeof(char *)
pShmNode->apRegion, nReqRegion*sizeof(char *)
);
if( !apNew ){
rc = SQLITE_IOERR_NOMEM;
goto shmpage_out;
}
pShmNode->apRegion = apNew;
while(pShmNode->nRegion<=iRegion){
while( pShmNode->nRegion<nReqRegion ){
int nMap = szRegion*nShmPerMap;
int i;
void *pMem;
if( pShmNode->h>=0 ){
pMem = osMmap(0, szRegion,
pMem = osMmap(0, nMap,
pShmNode->isReadonly ? PROT_READ : PROT_READ|PROT_WRITE,
MAP_SHARED, pShmNode->h, szRegion*(i64)pShmNode->nRegion
);
@@ -4418,8 +4453,11 @@ static int unixShmMap(
}
memset(pMem, 0, szRegion);
}
pShmNode->apRegion[pShmNode->nRegion] = pMem;
pShmNode->nRegion++;
for(i=0; i<nShmPerMap; i++){
pShmNode->apRegion[pShmNode->nRegion+i] = &((char*)pMem)[szRegion*i];
}
pShmNode->nRegion += nShmPerMap;
}
}
@@ -4633,19 +4671,6 @@ static void unixUnmapfile(unixFile *pFd){
}
}
/*
** Return the system page size.
*/
static int unixGetPagesize(void){
#if HAVE_MREMAP
return 512;
#elif defined(_BSD_SOURCE)
return getpagesize();
#else
return (int)sysconf(_SC_PAGESIZE);
#endif
}
/*
** Attempt to set the size of the memory mapping maintained by file
** descriptor pFd to nNew bytes. Any existing mapping is discarded.
@@ -4682,8 +4707,12 @@ static void unixRemapfile(
if( (pFd->ctrlFlags & UNIXFILE_RDONLY)==0 ) flags |= PROT_WRITE;
if( pOrig ){
#if HAVE_MREMAP
i64 nReuse = pFd->mmapSize;
#else
const int szSyspage = unixGetPagesize();
i64 nReuse = (pFd->mmapSize & ~(szSyspage-1));
#endif
u8 *pReq = &pOrig[nReuse];
/* Unmap any pages of the existing mapping that cannot be reused. */