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Refactor arenas array (fixes deadlock).

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Refactor the arenas array, which contains pointers to all extant arenas,
such that it starts out as a sparse array of maximum size, and use
double-checked atomics-based reads as the basis for fast and simple
arena_get().  Additionally, reduce arenas_lock's role such that it only
protects against arena initalization races.  These changes remove the
possibility for arena lookups to trigger locking, which resolves at
least one known (fork-related) deadlock.

This resolves #315.
This commit is contained in:
Jason Evans
2016-02-24 23:58:10 -08:00
parent 3812729167
commit 767d85061a
9 changed files with 162 additions and 214 deletions
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43
src/ctl.c
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@@ -694,9 +694,7 @@ ctl_grow(void)
static void
ctl_refresh(void)
{
tsd_t *tsd;
unsigned i;
bool refreshed;
VARIABLE_ARRAY(arena_t *, tarenas, ctl_stats.narenas);
/*
@@ -706,19 +704,14 @@ ctl_refresh(void)
ctl_stats.arenas[ctl_stats.narenas].nthreads = 0;
ctl_arena_clear(&ctl_stats.arenas[ctl_stats.narenas]);
tsd = tsd_fetch();
for (i = 0, refreshed = false; i < ctl_stats.narenas; i++) {
tarenas[i] = arena_get(tsd, i, false, false);
if (tarenas[i] == NULL && !refreshed) {
tarenas[i] = arena_get(tsd, i, false, true);
refreshed = true;
}
}
for (i = 0; i < ctl_stats.narenas; i++)
tarenas[i] = arena_get(i, false);
for (i = 0; i < ctl_stats.narenas; i++) {
if (tarenas[i] != NULL)
ctl_stats.arenas[i].nthreads = arena_nbound(i);
else
if (tarenas[i] != NULL) {
ctl_stats.arenas[i].nthreads =
arena_nthreads_get(arena_get(i, false));
} else
ctl_stats.arenas[i].nthreads = 0;
}
@@ -1332,7 +1325,7 @@ thread_arena_ctl(const size_t *mib, size_t miblen, void *oldp, size_t *oldlenp,
}
/* Initialize arena if necessary. */
newarena = arena_get(tsd, newind, true, true);
newarena = arena_get(newind, true);
if (newarena == NULL) {
ret = EAGAIN;
goto label_return;
@@ -1560,22 +1553,14 @@ arena_i_purge(unsigned arena_ind, bool all)
malloc_mutex_lock(&ctl_mtx);
{
tsd_t *tsd = tsd_fetch();
unsigned narenas = ctl_stats.narenas;
if (arena_ind == narenas) {
unsigned i;
bool refreshed;
VARIABLE_ARRAY(arena_t *, tarenas, narenas);
for (i = 0, refreshed = false; i < narenas; i++) {
tarenas[i] = arena_get(tsd, i, false, false);
if (tarenas[i] == NULL && !refreshed) {
tarenas[i] = arena_get(tsd, i, false,
true);
refreshed = true;
}
}
for (i = 0; i < narenas; i++)
tarenas[i] = arena_get(i, false);
/*
* No further need to hold ctl_mtx, since narenas and
@@ -1592,7 +1577,7 @@ arena_i_purge(unsigned arena_ind, bool all)
assert(arena_ind < narenas);
tarena = arena_get(tsd, arena_ind, false, true);
tarena = arena_get(arena_ind, false);
/* No further need to hold ctl_mtx. */
malloc_mutex_unlock(&ctl_mtx);
@@ -1664,7 +1649,7 @@ arena_i_dss_ctl(const size_t *mib, size_t miblen, void *oldp, size_t *oldlenp,
}
if (arena_ind < ctl_stats.narenas) {
arena_t *arena = arena_get(tsd_fetch(), arena_ind, false, true);
arena_t *arena = arena_get(arena_ind, false);
if (arena == NULL || (dss_prec != dss_prec_limit &&
arena_dss_prec_set(arena, dss_prec))) {
ret = EFAULT;
@@ -1697,7 +1682,7 @@ arena_i_lg_dirty_mult_ctl(const size_t *mib, size_t miblen, void *oldp,
unsigned arena_ind = (unsigned)mib[1];
arena_t *arena;
arena = arena_get(tsd_fetch(), arena_ind, false, true);
arena = arena_get(arena_ind, false);
if (arena == NULL) {
ret = EFAULT;
goto label_return;
@@ -1731,7 +1716,7 @@ arena_i_decay_time_ctl(const size_t *mib, size_t miblen, void *oldp,
unsigned arena_ind = (unsigned)mib[1];
arena_t *arena;
arena = arena_get(tsd_fetch(), arena_ind, false, true);
arena = arena_get(arena_ind, false);
if (arena == NULL) {
ret = EFAULT;
goto label_return;
@@ -1767,7 +1752,7 @@ arena_i_chunk_hooks_ctl(const size_t *mib, size_t miblen, void *oldp,
malloc_mutex_lock(&ctl_mtx);
if (arena_ind < narenas_total_get() && (arena =
arena_get(tsd_fetch(), arena_ind, false, true)) != NULL) {
arena_get(arena_ind, false)) != NULL) {
if (newp != NULL) {
chunk_hooks_t old_chunk_hooks, new_chunk_hooks;
WRITE(new_chunk_hooks, chunk_hooks_t);