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Fix possible "nmalloc >= ndalloc" assertion

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In arena_stats_merge() first nmalloc was read, and after ndalloc.

However with this order, it is possible for some thread to incement
ndalloc in between, and then nmalloc < ndalloc, and assertion will fail,
like again found by ClickHouse CI [1] (even after #2234).

  [1]: https://github.com/ClickHouse/ClickHouse/issues/31531

Swap the order to avoid possible assertion.

Cc: @interwq
Follow-up for: #2234
This commit is contained in:
Azat Khuzhin 2022-07-03 20:23:59 +03:00 committed by Qi Wang
parent a9215bf18a
commit cb578bbe01
1 changed files with 9 additions and 6 deletions
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15
src/arena.c
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@ -106,18 +106,21 @@ arena_stats_merge(tsdn_t *tsdn, arena_t *arena, unsigned *nthreads,
astats->metadata_thp += metadata_thp;
for (szind_t i = 0; i < SC_NSIZES - SC_NBINS; i++) {
uint64_t nmalloc = locked_read_u64(tsdn,
LOCKEDINT_MTX(arena->stats.mtx),
&arena->stats.lstats[i].nmalloc);
locked_inc_u64_unsynchronized(&lstats[i].nmalloc, nmalloc);
astats->nmalloc_large += nmalloc;
/* ndalloc should be read before nmalloc,
* since otherwise it is possible for ndalloc to be incremented,
* and the following can become true: ndalloc > nmalloc */
uint64_t ndalloc = locked_read_u64(tsdn,
LOCKEDINT_MTX(arena->stats.mtx),
&arena->stats.lstats[i].ndalloc);
locked_inc_u64_unsynchronized(&lstats[i].ndalloc, ndalloc);
astats->ndalloc_large += ndalloc;
uint64_t nmalloc = locked_read_u64(tsdn,
LOCKEDINT_MTX(arena->stats.mtx),
&arena->stats.lstats[i].nmalloc);
locked_inc_u64_unsynchronized(&lstats[i].nmalloc, nmalloc);
astats->nmalloc_large += nmalloc;
uint64_t nrequests = locked_read_u64(tsdn,
LOCKEDINT_MTX(arena->stats.mtx),
&arena->stats.lstats[i].nrequests);