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Potential atomic property/init deadlock fix #285

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Potential atomic property/init deadlock fix #285

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12 changes: 7 additions & 5 deletions associate.m
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@
#include "lock.h"
#include "gc_ops.h"

PRIVATE int associate_spinlocks[spinlock_count];

/**
* A single associative reference. Contains the key, value, and association
* policy.
Expand Down Expand Up @@ -140,7 +142,7 @@ static void setReference(struct reference_list *list,
break;
}
// While inserting into the list, we need to lock it temporarily.
volatile int *lock = lock_for_pointer(list);
volatile int *lock = associate_lock_for_pointer(list);
lock_spinlock(lock);
struct reference *r = findReference(list, key);
// If there's an existing reference, then we can update it, otherwise we
Expand All @@ -165,7 +167,7 @@ static void setReference(struct reference_list *list,
BOOL needLock = isAtomic(r->policy) || isAtomic(policy);
if (needLock)
{
lock = lock_for_pointer(r);
lock = associate_lock_for_pointer(r);
lock_spinlock(lock);
}
@try
Expand Down Expand Up @@ -289,7 +291,7 @@ static void deallocHiddenClass(id obj, SEL _cmd)
Class cls = (Class)object;
if ((NULL == cls->extra_data) && create)
{
volatile int *lock = lock_for_pointer(cls);
volatile int *lock = associate_lock_for_pointer(cls);
struct reference_list *list = gc->malloc(sizeof(struct reference_list));
lock_spinlock(lock);
if (NULL == cls->extra_data)
Expand All @@ -309,7 +311,7 @@ static void deallocHiddenClass(id obj, SEL _cmd)
Class hiddenClass = findHiddenClass(object);
if ((NULL == hiddenClass) && create)
{
volatile int *lock = lock_for_pointer(object);
volatile int *lock = associate_lock_for_pointer(object);
lock_spinlock(lock);
hiddenClass = findHiddenClass(object);
if (NULL == hiddenClass)
Expand Down Expand Up @@ -423,7 +425,7 @@ static Class hiddenClassForObject(id object)
Class hiddenClass = findHiddenClass(object);
if (NULL == hiddenClass)
{
volatile int *lock = lock_for_pointer(object);
volatile int *lock = associate_lock_for_pointer(object);
lock_spinlock(lock);
hiddenClass = findHiddenClass(object);
if (NULL == hiddenClass)
Expand Down
39 changes: 22 additions & 17 deletions properties.m
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@
#include "gc_ops.h"
#include "lock.h"

PRIVATE int spinlocks[spinlock_count];
PRIVATE int prop_spinlocks[spinlock_count];

/**
* Public function for getting a property.
Expand All @@ -26,7 +26,7 @@ id objc_getProperty(id obj, SEL _cmd, ptrdiff_t offset, BOOL isAtomic)
id ret;
if (isAtomic)
{
volatile int *lock = lock_for_pointer(addr);
volatile int *lock = prop_lock_for_pointer(addr);
lock_spinlock(lock);
ret = *(id*)addr;
ret = objc_retain(ret);
Expand Down Expand Up @@ -59,7 +59,7 @@ void objc_setProperty(id obj, SEL _cmd, ptrdiff_t offset, id arg, BOOL isAtomic,
id old;
if (isAtomic)
{
volatile int *lock = lock_for_pointer(addr);
volatile int *lock = prop_lock_for_pointer(addr);
lock_spinlock(lock);
old = *(id*)addr;
*(id*)addr = arg;
Expand All @@ -79,7 +79,7 @@ void objc_setProperty_atomic(id obj, SEL _cmd, id arg, ptrdiff_t offset)
char *addr = (char*)obj;
addr += offset;
arg = objc_retain(arg);
volatile int *lock = lock_for_pointer(addr);
volatile int *lock = prop_lock_for_pointer(addr);
lock_spinlock(lock);
id old = *(id*)addr;
*(id*)addr = arg;
Expand All @@ -94,7 +94,7 @@ void objc_setProperty_atomic_copy(id obj, SEL _cmd, id arg, ptrdiff_t offset)
addr += offset;

arg = [arg copy];
volatile int *lock = lock_for_pointer(addr);
volatile int *lock = prop_lock_for_pointer(addr);
lock_spinlock(lock);
id old = *(id*)addr;
*(id*)addr = arg;
Expand Down Expand Up @@ -127,20 +127,25 @@ void objc_setProperty_nonatomic_copy(id obj, SEL _cmd, id arg, ptrdiff_t offset)
void objc_copyCppObjectAtomic(void *dest, const void *src,
void (*copyHelper) (void *dest, const void *source))
{
volatile int *lock = lock_for_pointer(src < dest ? src : dest);
volatile int *lock2 = lock_for_pointer(src < dest ? dest : src);
volatile int *lock = prop_lock_for_pointer(src < dest ? src : dest);
volatile int *lock2 = prop_lock_for_pointer(src < dest ? dest : src);
lock_spinlock(lock);
lock_spinlock(lock2);
if (lock != lock2) {
// this might look odd, but anytime we take two spinlocks simutaniously, there
// is a non-zero chance that the pointers might hash to the same spinlock.
// in which cause, locking one locks both, and locking both would deadlock us.
lock_spinlock(lock2);
}
copyHelper(dest, src);
unlock_spinlock(lock);
unlock_spinlock(lock2);
if (lock != lock2) { unlock_spinlock(lock2); }
}

OBJC_PUBLIC
void objc_getCppObjectAtomic(void *dest, const void *src,
void (*copyHelper) (void *dest, const void *source))
{
volatile int *lock = lock_for_pointer(src);
volatile int *lock = prop_lock_for_pointer(src);
lock_spinlock(lock);
copyHelper(dest, src);
unlock_spinlock(lock);
Expand All @@ -150,7 +155,7 @@ void objc_getCppObjectAtomic(void *dest, const void *src,
void objc_setCppObjectAtomic(void *dest, const void *src,
void (*copyHelper) (void *dest, const void *source))
{
volatile int *lock = lock_for_pointer(dest);
volatile int *lock = prop_lock_for_pointer(dest);
lock_spinlock(lock);
copyHelper(dest, src);
unlock_spinlock(lock);
Expand All @@ -172,13 +177,13 @@ void objc_copyPropertyStruct(void *dest,
{
if (atomic)
{
volatile int *lock = lock_for_pointer(src < dest ? src : dest);
volatile int *lock2 = lock_for_pointer(src < dest ? dest : src);
volatile int *lock = prop_lock_for_pointer(src < dest ? src : dest);
volatile int *lock2 = prop_lock_for_pointer(src < dest ? dest : src);
lock_spinlock(lock);
lock_spinlock(lock2);
if (lock != lock2) { lock_spinlock(lock2); }
memcpy(dest, src, size);
unlock_spinlock(lock);
unlock_spinlock(lock2);
if (lock != lock2) { unlock_spinlock(lock2); }
}
else
{
Expand All @@ -199,7 +204,7 @@ void objc_getPropertyStruct(void *dest,
{
if (atomic)
{
volatile int *lock = lock_for_pointer(src);
volatile int *lock = prop_lock_for_pointer(src);
lock_spinlock(lock);
memcpy(dest, src, size);
unlock_spinlock(lock);
Expand All @@ -223,7 +228,7 @@ void objc_setPropertyStruct(void *dest,
{
if (atomic)
{
volatile int *lock = lock_for_pointer(dest);
volatile int *lock = prop_lock_for_pointer(dest);
lock_spinlock(lock);
memcpy(dest, src, size);
unlock_spinlock(lock);
Expand Down
30 changes: 21 additions & 9 deletions spinlock.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,20 @@ static const int spinlock_mask = spinlock_count - 1;
/**
* Integers used as spinlocks for atomic property access.
*/
extern int spinlocks[spinlock_count];
extern int prop_spinlocks[spinlock_count];
extern int associate_spinlocks[spinlock_count];

static inline intptr_t hash_for_pointer(const void *ptr)
{
intptr_t hash = (intptr_t)ptr;
// Most properties will be pointers, so disregard the lowest few bits
hash >>= sizeof(void*) == 4 ? 2 : 8;
intptr_t low = hash & spinlock_mask;
hash >>= 16;
hash |= low;
return (hash & spinlock_mask);
}

/**
* Get a spin lock from a pointer. We want to prevent lock contention between
* properties in the same object - if someone is stupid enough to be using
Expand All @@ -26,15 +39,14 @@ extern int spinlocks[spinlock_count];
* contention between the same property in different objects, so we can't just
* use the ivar offset.
*/
static inline volatile int *lock_for_pointer(const void *ptr)
static inline volatile int *prop_lock_for_pointer(const void *ptr)
{
intptr_t hash = (intptr_t)ptr;
// Most properties will be pointers, so disregard the lowest few bits
hash >>= sizeof(void*) == 4 ? 2 : 8;
intptr_t low = hash & spinlock_mask;
hash >>= 16;
hash |= low;
return spinlocks + (hash & spinlock_mask);
return prop_spinlocks + hash_for_pointer(ptr);
}

static inline volatile int *associate_lock_for_pointer(const void *ptr)
{
return associate_spinlocks + hash_for_pointer(ptr);
}

/**
Expand Down
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