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Do not assume dss never decreases.

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An sbrk() caller outside jemalloc can decrease the dss, so add a
separate atomic boolean to explicitly track whether jemalloc is
concurrently calling sbrk(), rather than depending on state outside
jemalloc's full control.

Fixes #802 for stable-4
This commit is contained in:
Uwe L. Korn 2017-08-29 11:06:50 +02:00 • committed by Qi Wang
parent 7883c7749f
commit 17c897976c
1 changed files with 35 additions and 36 deletions
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71
src/chunk_dss.c
View file

@ -20,6 +20,8 @@ static unsigned dss_prec_default = (unsigned)DSS_PREC_DEFAULT;
/* Base address of the DSS. */
static void *dss_base;
/* Atomic boolean indicating whether a thread is currently extending DSS. */
static unsigned dss_extending;
/* Atomic boolean indicating whether the DSS is exhausted. */
static unsigned dss_exhausted;
/* Atomic current upper limit on DSS addresses. */
@ -63,29 +65,13 @@ chunk_dss_prec_set(dss_prec_t dss_prec)
static void *
chunk_dss_max_update(void *new_addr)
{
void *max_cur;
spin_t spinner;
void *max_cur = chunk_dss_sbrk(0);
/*
* Get the current end of the DSS as max_cur and assure that dss_max is
* up to date.
*/
spin_init(&spinner);
while (true) {
void *max_prev = atomic_read_p(&dss_max);
max_cur = chunk_dss_sbrk(0);
if ((uintptr_t)max_prev > (uintptr_t)max_cur) {
/*
* Another thread optimistically updated dss_max. Wait
* for it to finish.
*/
spin_adaptive(&spinner);
continue;
}
if (!atomic_cas_p(&dss_max, max_prev, max_cur))
break;
if (max_cur == (void *)-1) {
return NULL;
}
atomic_write_p(&dss_max, max_cur);
/* Fixed new_addr can only be supported if it is at the edge of DSS. */
if (new_addr != NULL && max_cur != new_addr)
return (NULL);
@ -93,6 +79,26 @@ chunk_dss_max_update(void *new_addr)
return (max_cur);
}
static void
chunk_dss_extending_start(void) {
spin_t spinner;
spin_init(&spinner);
while (true) {
unsigned expected = 0;
if (!atomic_cas_u(&dss_extending, expected, 1)) {
break;
}
spin_adaptive(&spinner);
}
}
static void
chunk_dss_extending_finish(void) {
assert(atomic_read_u(&dss_extending));
atomic_write_u(&dss_extending, 0);
}
void *
chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
size_t alignment, bool *zero, bool *commit)
@ -108,6 +114,7 @@ chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
if ((intptr_t)size < 0)
return (NULL);
chunk_dss_extending_start();
if (!atomic_read_u(&dss_exhausted)) {
/*
* The loop is necessary to recover from races with other
@ -152,19 +159,14 @@ chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
assert((uintptr_t)max_cur + incr == (uintptr_t)ret +
size);
/*
* Optimistically update dss_max, and roll back below if
* sbrk() fails. No other thread will try to extend the
* DSS while dss_max is greater than the current DSS
* max reported by sbrk(0).
*/
if (atomic_cas_p(&dss_max, max_cur, dss_next))
continue;
/* Try to allocate. */
dss_prev = chunk_dss_sbrk(incr);
if (dss_prev == max_cur) {
/* Success. */
atomic_write_p(&dss_max, dss_next);
chunk_dss_extending_finish();
if (gap_size_chunk != 0) {
chunk_hooks_t chunk_hooks =
CHUNK_HOOKS_INITIALIZER;
@ -186,13 +188,8 @@ chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
/*
* Failure, whether due to OOM or a race with a raw
* sbrk() call from outside the allocator. Try to roll
* back optimistic dss_max update; if rollback fails,
* it's due to another caller of this function having
* succeeded since this invocation started, in which
* case rollback is not necessary.
* sbrk() call from outside the allocator.
*/
atomic_cas_p(&dss_max, dss_next, max_cur);
if (dss_prev == (void *)-1) {
/* OOM. */
atomic_write_u(&dss_exhausted, (unsigned)true);
@ -201,6 +198,7 @@ chunk_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
}
}
label_oom:
chunk_dss_extending_finish();
return (NULL);
}
@ -240,6 +238,7 @@ chunk_dss_boot(void)
cassert(have_dss);
dss_base = chunk_dss_sbrk(0);
atomic_write_u(&dss_extending, 0);
dss_exhausted = (unsigned)(dss_base == (void *)-1);
dss_max = dss_base;
}