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Fix a deadlock due to an ABA like bug.

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This commit is contained in:
Patrick Pelissier committed 2018-02-19 19:00:24 +01:00
1 parent 057d783158
commit 3d59fb0d9a
1 file changed
+26 -18
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m-genint.h
+26 -18
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@@ -49,8 +49,8 @@
typedef unsigned long long genint_limb_t;
typedef struct genint_s {
size_t n; // size of the container
size_t max; // number of allocated limb - 1
unsigned int n; // size of the container
unsigned int max; // number of allocated limb - 1
genint_limb_t mask0; // mask of the last limb
genint_limb_t mask_master; // mask of master
atomic_ullong master; // master bitfield (which informs if a limb is full or not)
@@ -68,9 +68,20 @@ typedef struct genint_s {
#define GENINT_ONE ((genint_limb_t)1)
#define GENINT_ABA_CPT 32
#define GENINT_ABA_CPT_T uint32_t
#define GENINT_MASTER_SET(master, i) \
((((master)& (~((GENINT_ONE<< GENINT_ABA_CPT)-1))) | (GENINT_ONE << (GENINT_LIMBSIZE - 1 - i))) \
|((GENINT_ABA_CPT_T)((master) + 1)))
#define GENINT_MASTER_RESET(master, i) \
(((master) & (~((GENINT_ONE<< GENINT_ABA_CPT)-1)) & ~(GENINT_ONE << (GENINT_LIMBSIZE - 1 - i))) \
|((GENINT_ABA_CPT_T)((master) + 1)))
static inline void genint_init(genint_t s, size_t n)
{
assert (s != NULL && n > 0 && n <= GENINT_LIMBSIZE * GENINT_LIMBSIZE);
assert (s != NULL && n > 0 && n <= GENINT_LIMBSIZE * (GENINT_LIMBSIZE - GENINT_ABA_CPT));
const size_t alloc = (n + GENINT_LIMBSIZE - 1) / GENINT_LIMBSIZE;
const size_t index = n % GENINT_LIMBSIZE;
atomic_ullong *ptr = M_MEMORY_REALLOC (atomic_ullong, NULL, alloc);
@@ -82,7 +93,7 @@ static inline void genint_init(genint_t s, size_t n)
s->data = ptr;
s->max = alloc-1;
s->mask0 = (index == 0) ? -GENINT_ONE : ~((GENINT_ONE<<(GENINT_LIMBSIZE-index))-1);
s->mask_master = ((GENINT_ONE << alloc) - 1) << (GENINT_LIMBSIZE-alloc);
s->mask_master = (((GENINT_ONE << alloc) - 1) << (GENINT_LIMBSIZE-alloc)) >> GENINT_ABA_CPT;
atomic_init (&s->master, (genint_limb_t)0);
for(size_t i = 0; i < alloc; i++)
atomic_init(&s->data[i], (genint_limb_t)0);
@@ -103,11 +114,12 @@ static inline size_t genint_pop(genint_t s)
// First read master to see which limb is not full.
genint_limb_t master = atomic_load(&s->master);
// While master is not full
while (master != s->mask_master) {
while ((master >> GENINT_ABA_CPT) != s->mask_master) {
// Let's get the index i of the first not full limb according to master.
unsigned int i = m_core_clz(~master);
// Let's compute the mask of this limb representing the limb as being full
const size_t mask = (i == s->max) ? s->mask0 : -GENINT_ONE;
size_t mask = s->mask0;
mask = (i == s->max) ? mask : -GENINT_ONE;
unsigned int bit;
// Let's load this limb,
genint_limb_t next, org = atomic_load(&s->data[i]);
@@ -126,8 +138,7 @@ static inline size_t genint_pop(genint_t s)
// We have reserved the integer.
// If the limb is now full, try to update master
while (M_UNLIKELY(next == mask
&& !atomic_compare_exchange_weak (&s->master, &master, master|(GENINT_ONE << (GENINT_LIMBSIZE - 1 - i) ))
&& ((master & (GENINT_ONE << (GENINT_LIMBSIZE - 1 - i))) == 0) )) {
&& !atomic_compare_exchange_weak (&s->master, &master, GENINT_MASTER_SET(master, i)))) {
// Fail to update. Reload limb to check if it is still full.
next = atomic_load(&s->data[i]);
}
@@ -147,8 +158,9 @@ static inline void genint_push(genint_t s, size_t n)
{
GENINT_CONTRACT(s);
assert (n < s->n);
size_t i = n / GENINT_LIMBSIZE;
size_t bit = GENINT_LIMBSIZE - 1 - (n % GENINT_LIMBSIZE);
const size_t i = n / GENINT_LIMBSIZE;
const size_t bit = GENINT_LIMBSIZE - 1 - (n % GENINT_LIMBSIZE);
genint_limb_t master = atomic_load(&s->master);
// Load the limb
genint_limb_t next, org = atomic_load(&s->data[i]);
do {
@@ -157,18 +169,14 @@ static inline void genint_push(genint_t s, size_t n)
next = org & (~(GENINT_ONE << bit));
// Try to unreserve it.
} while (!atomic_compare_exchange_weak (&s->data[i], &org, next));
genint_limb_t master = atomic_load(&s->master);
genint_limb_t mask_i = GENINT_ONE << (GENINT_LIMBSIZE - 1 - i);
// if the limb was marked as full by master
if (M_UNLIKELY (master & mask_i)) {
// Let's try to update master to reflech that limb is not full
while (!atomic_compare_exchange_weak (&s->master, &master, master & (~mask_i)) && (master & mask_i)) {
// Fail to update master. Check if limb is still free
const size_t mask = (i == s->max) ? s->mask0 : -GENINT_ONE;
org = atomic_load(&s->data[i]);
if (org == mask)
// Limb is full once again. Stop
return;
while ((next&(GENINT_ONE << bit)) == 0
&& !atomic_compare_exchange_weak (&s->master, &master, GENINT_MASTER_RESET(master, i))) {
// Fail to update master.
next = atomic_load(&s->data[i]);
}
}
GENINT_CONTRACT(s);