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Fix extent_record().

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Read adjacent rtree elements while holding element locks, since the
extents mutex only protects against relevant like-state extent mutation.

Fix management of the 'coalesced' loop state variable to merge
forward/backward results, rather than overwriting the result of forward
coalescing if attempting to coalesce backward.  In practice this caused
no correctness issues, but could cause extra iterations in rare cases.

These regressions were introduced by
d27f29b468 (Disentangle arena and extent
locking.).
This commit is contained in:
Jason Evans 2017-02-05 23:59:53 -08:00
parent 6737d5f61e
commit 5177995530
1 changed files with 33 additions and 18 deletions
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51
src/extent.c
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@ -1035,12 +1035,9 @@ extent_can_coalesce(const extent_t *a, const extent_t *b) {
}
static bool
extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
extent_hooks_t **r_extent_hooks, extent_t *a, extent_t *b,
extents_t *extents) {
if (!extent_can_coalesce(a, b)) {
return true;
}
extent_coalesce(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
extent_t *a, extent_t *b, extents_t *extents) {
assert(extent_can_coalesce(a, b));
assert(extent_arena_get(a) == arena);
assert(extent_arena_get(b) == arena);
@ -1062,7 +1059,6 @@ extent_try_coalesce(tsdn_t *tsdn, arena_t *arena,
static void
extent_record(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
extents_t *extents, extent_t *extent) {
extent_t *prev, *next;
rtree_ctx_t rtree_ctx_fallback;
rtree_ctx_t *rtree_ctx = tsdn_rtree_ctx(tsdn, &rtree_ctx_fallback);
@ -1090,21 +1086,40 @@ extent_record(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
coalesced = false;
/* Try to coalesce forward. */
next = rtree_read(tsdn, &extents_rtree, rtree_ctx,
(uintptr_t)extent_past_get(extent), false);
if (next != NULL) {
coalesced = !extent_try_coalesce(tsdn, arena,
r_extent_hooks, extent, next, extents);
rtree_elm_t *next_elm = rtree_elm_acquire(tsdn, &extents_rtree,
rtree_ctx, (uintptr_t)extent_past_get(extent), false,
false);
if (next_elm != NULL) {
extent_t *next = rtree_elm_read_acquired(tsdn,
&extents_rtree, next_elm);
/*
* extents->mtx only protects against races for
* like-state extents, so call extent_can_coalesce()
* before releasing the next_elm lock.
*/
bool can_coalesce = (next != NULL &&
extent_can_coalesce(extent, next));
rtree_elm_release(tsdn, &extents_rtree, next_elm);
if (can_coalesce && !extent_coalesce(tsdn, arena,
r_extent_hooks, extent, next, extents)) {
coalesced = true;
}
}
/* Try to coalesce backward. */
prev = rtree_read(tsdn, &extents_rtree, rtree_ctx,
(uintptr_t)extent_before_get(extent), false);
if (prev != NULL) {
coalesced = !extent_try_coalesce(tsdn, arena,
r_extent_hooks, prev, extent, extents);
if (coalesced) {
rtree_elm_t *prev_elm = rtree_elm_acquire(tsdn, &extents_rtree,
rtree_ctx, (uintptr_t)extent_before_get(extent), false,
false);
if (prev_elm != NULL) {
extent_t *prev = rtree_elm_read_acquired(tsdn,
&extents_rtree, prev_elm);
bool can_coalesce = (prev != NULL &&
extent_can_coalesce(prev, extent));
rtree_elm_release(tsdn, &extents_rtree, prev_elm);
if (can_coalesce && !extent_coalesce(tsdn, arena,
r_extent_hooks, prev, extent, extents)) {
extent = prev;
coalesced = true;
}
}
} while (coalesced);