X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=blobdiff_plain;f=snapshot.cc;h=1e7d80b4b5d836d1c4a1cdb653824a626afb82c8;hp=51d2a3adbb4842902db2fab53ceda4f61dbb48d9;hb=f48c73aeda479368d4bfaf96fe9fe07f3d3d8bdb;hpb=f24d5521d1fcb0d710a2b8107aa5782e8ce430b6 diff --git a/snapshot.cc b/snapshot.cc index 51d2a3ad..1e7d80b4 100644 --- a/snapshot.cc +++ b/snapshot.cc @@ -28,23 +28,47 @@ /* extern declaration definition */ #if USE_MPROTECT_SNAPSHOT struct SnapShot * snapshotrecord = NULL; -struct Snapshot_t * sTheRecord = NULL; #else -struct Snapshot_t * sTheRecord = NULL; +struct Snapshot * sTheRecord = NULL; #endif #if !USE_MPROTECT_SNAPSHOT +/** @statics +* These variables are necessary because the stack is shared region and +* there exists a race between all processes executing the same function. +* To avoid the problem above, we require variables allocated in 'safe' regions. +* The bug was actually observed with the forkID, these variables below are +* used to indicate the various contexts to which to switch to. +* +* @savedSnapshotContext: contains the point to which takesnapshot() call should switch to. +* @savedUserSnapshotContext: contains the point to which the process whose snapshotid is equal to the rollbackid should switch to +* @snapshotid: it is a running counter for the various forked processes snapshotid. it is incremented and set in a persistently shared record +*/ static ucontext_t savedSnapshotContext; static ucontext_t savedUserSnapshotContext; static snapshot_id snapshotid = 0; #endif +/** PageAlignedAdressUpdate return a page aligned address for the + * address being added as a side effect the numBytes are also changed. + */ +static void * PageAlignAddressUpward(void * addr) { + return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1)); +} + #if USE_MPROTECT_SNAPSHOT +/** ReturnPageAlignedAddress returns a page aligned address for the + * address being added as a side effect the numBytes are also changed. + */ +static void * ReturnPageAlignedAddress(void * addr) { + return (void *)(((uintptr_t)addr)&~(PAGESIZE-1)); +} + /** The initSnapShotRecord method initialized the snapshotting data * structures for the mprotect based snapshot. */ -void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) { +static void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, unsigned int nummemoryregions) { snapshotrecord=( struct SnapShot * )MYMALLOC(sizeof(struct SnapShot)); snapshotrecord->regionsToSnapShot=( struct MemoryRegion * )MYMALLOC(sizeof(struct MemoryRegion)*nummemoryregions); snapshotrecord->backingStoreBasePtr= ( struct SnapShotPage * )MYMALLOC( sizeof( struct SnapShotPage ) * (numbackingpages + 1) ); @@ -59,14 +83,11 @@ void initSnapShotRecord(unsigned int numbackingpages, unsigned int numsnapshots, snapshotrecord->maxBackingPages=numbackingpages; snapshotrecord->maxSnapShots=numsnapshots; } -#endif //nothing to initialize for the fork based snapshotting. /** HandlePF is the page fault handler for mprotect based snapshotting * algorithm. */ - -void HandlePF( int sig, siginfo_t *si, void * unused){ -#if USE_MPROTECT_SNAPSHOT +static void HandlePF( int sig, siginfo_t *si, void * unused){ if( si->si_code == SEGV_MAPERR ){ printf("Real Fault at %p\n", si->si_addr); exit( EXIT_FAILURE ); @@ -88,48 +109,30 @@ void HandlePF( int sig, siginfo_t *si, void * unused){ perror("mprotect"); // Handle error by quitting? } -#endif //nothing to handle for non snapshotting case. -} - -/** ReturnPageAlignedAddress returns a page aligned address for the - * address being added as a side effect the numBytes are also changed. - */ - -void * ReturnPageAlignedAddress(void * addr) { - return (void *)(((uintptr_t)addr)&~(PAGESIZE-1)); } +#endif //nothing to handle for non snapshotting case. -/** PageAlignedAdressUpdate return a page aligned address for the - * address being added as a side effect the numBytes are also changed. - */ - -void * PageAlignAddressUpward(void * addr) { - return (void *)((((uintptr_t)addr)+PAGESIZE-1)&~(PAGESIZE-1)); -} -#ifdef __cplusplus -extern "C" { -#endif - void createSharedLibrary(){ +void createSharedLibrary(){ #if !USE_MPROTECT_SNAPSHOT - //step 1. create shared memory. - if( sTheRecord ) return; - int fd = shm_open( "/ModelChecker-Snapshotter", O_RDWR | O_CREAT, 0777 ); //universal permissions. - if( -1 == fd ) FAILURE("shm_open"); - if( -1 == ftruncate( fd, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT ) ) FAILURE( "ftruncate" ); - char * memMapBase = ( char * ) mmap( 0, ( size_t )SHARED_MEMORY_DEFAULT + ( size_t )STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 ); - if( MAP_FAILED == memMapBase ) FAILURE("mmap"); - sTheRecord = ( struct Snapshot_t * )memMapBase; - sTheRecord->mSharedMemoryBase = memMapBase + sizeof( struct Snapshot_t ); - sTheRecord->mStackBase = ( char * )memMapBase + ( size_t )SHARED_MEMORY_DEFAULT; - sTheRecord->mStackSize = STACK_SIZE_DEFAULT; - sTheRecord->mIDToRollback = -1; - sTheRecord->currSnapShotID = 0; - sTheRecord->mbFinalize = false; + //step 1. create shared memory. + if ( sTheRecord ) + return; + int fd = shm_open( "/ModelChecker-Snapshotter", O_RDWR | O_CREAT, 0777 ); //universal permissions. + if ( -1 == fd ) + FAILURE("shm_open"); + if ( -1 == ftruncate( fd, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT ) ) + FAILURE( "ftruncate" ); + void * memMapBase = mmap( 0, SHARED_MEMORY_DEFAULT + STACK_SIZE_DEFAULT, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 ); + if( MAP_FAILED == memMapBase ) + FAILURE("mmap"); + sTheRecord = ( struct Snapshot * )memMapBase; + sTheRecord->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(struct Snapshot)); + sTheRecord->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT); + sTheRecord->mStackSize = STACK_SIZE_DEFAULT; + sTheRecord->mIDToRollback = -1; + sTheRecord->currSnapShotID = 0; #endif - } -#ifdef __cplusplus } -#endif /** The initSnapShotLibrary function initializes the Snapshot library. * @param entryPoint the function that should run the program. @@ -185,37 +188,28 @@ void initSnapShotLibrary(unsigned int numbackingpages, createSharedLibrary(); //step 2 setup the stack context. - - int alreadySwapped = 0; - getcontext( &savedSnapshotContext ); - if( !alreadySwapped ){ - alreadySwapped = 1; - ucontext_t currentContext, swappedContext, newContext; - getcontext( &newContext ); - newContext.uc_stack.ss_sp = sTheRecord->mStackBase; - newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT; - newContext.uc_link = ¤tContext; - makecontext( &newContext, entryPoint, 0 ); - swapcontext( &swappedContext, &newContext ); - } - - //add the code to take a snapshot here... - //to return to user process, do a second swapcontext... + ucontext_t newContext; + getcontext( &newContext ); + newContext.uc_stack.ss_sp = sTheRecord->mStackBase; + newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT; + makecontext( &newContext, entryPoint, 0 ); + /* switch to a new entryPoint context, on a new stack */ + swapcontext(&savedSnapshotContext, &newContext); + + /* switch back here when takesnapshot is called */ pid_t forkedID = 0; snapshotid = sTheRecord->currSnapShotID; bool swapContext = false; - while( !sTheRecord->mbFinalize ){ + while( true ){ sTheRecord->currSnapShotID=snapshotid+1; forkedID = fork(); if( 0 == forkedID ){ ucontext_t currentContext; -#if 0 - int dbg = 0; - while( !dbg ); -#endif + /*If the rollback bool is set{ see below }, switch to the context we need to return to during a rollback*/ if( swapContext ) swapcontext( ¤tContext, &( sTheRecord->mContextToRollback ) ); else{ + /*Child process which is forked as a result of takesnapshot call should switch back to the takesnapshot context*/ swapcontext( ¤tContext, &savedUserSnapshotContext ); } } else { @@ -232,6 +226,7 @@ void initSnapShotLibrary(unsigned int numbackingpages, if( sTheRecord->mIDToRollback != snapshotid ) exit(EXIT_SUCCESS); else{ + /*This bool indicates that the current process's snapshotid is same as the id to which the rollback needs to occur*/ swapContext = true; } } @@ -258,7 +253,6 @@ void addMemoryRegionToSnapShot( void * addr, unsigned int numPages) { /** The takeSnapshot function takes a snapshot. * @return The snapshot identifier. */ - snapshot_id takeSnapshot( ){ #if USE_MPROTECT_SNAPSHOT for(unsigned int region=0; regionlastRegion;region++) { @@ -285,7 +279,6 @@ snapshot_id takeSnapshot( ){ /** The rollBack function rollback to the given snapshot identifier. * @param theID is the snapshot identifier to rollback to. */ - void rollBack( snapshot_id theID ){ #if USE_MPROTECT_SNAPSHOT std::map< void *, bool, std::less< void * >, MyAlloc< std::pair< const void *, bool > > > duplicateMap; @@ -315,21 +308,21 @@ void rollBack( snapshot_id theID ){ sTheRecord->mIDToRollback = theID; int sTemp = 0; getcontext( &sTheRecord->mContextToRollback ); + /* + * This is used to quit the process on rollback, so that + * the process which needs to rollback can quit allowing the process whose snapshotid matches the rollbackid to switch to + * this context and continue.... + */ if( !sTemp ){ sTemp = 1; SSDEBUG("Invoked rollback"); exit(EXIT_SUCCESS); } -#endif -} - -/** The finalize method shuts down the snapshotting system. */ -//Subramanian -- remove this function from the external interface and -//have us call it internally - -void finalize(){ -#if !USE_MPROTECT_SNAPSHOT - sTheRecord->mbFinalize = true; + /* + * This fix obviates the need for a finalize call. hence less dependences for model-checker.... + * + */ + sTheRecord->mIDToRollback = -1; #endif }